WIP migrating over from `ammonite.ops` to `os` module.

__.compile works, haven't run tests yet

105 files changed, 708 insertions, 796 deletions

diff --git a/.appveyor.yml b/.appveyor.yml
index 1bd0c4c7..4cd5bfa0 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -33,7 +33,7 @@ build_script:
       cmd /C C:\mill\out\release\dest\mill.bat -i all main.test scalajslib.test)
   - if [%COMPILER%]==[msys2] (
       SET "PATH=%JAVA_HOME%\bin;C:\%MSYS2_DIR%\%MSYSTEM%\bin;C:\%MSYS2_DIR%\usr\bin;%PATH%" &&
-      C:\%MSYS2_DIR%\usr\bin\bash -lc 'mkdir -p /usr/local/bin' &&
+      C:\%MSYS2_DIR%\usr\bin\bash -lc 'os.makeDir.all -p /usr/local/bin' &&
       C:\%MSYS2_DIR%\usr\bin\bash -lc "curl -Lo /usr/local/bin/mill %MILL_URL%" &&
       C:\%MSYS2_DIR%\usr\bin\bash -lc 'chmod +x /usr/local/bin/mill' &&
       C:\%MSYS2_DIR%\usr\bin\bash -lc "cd /c/mill && mill -i dev.assembly" &&
@@ -41,7 +41,7 @@ build_script:
       C:\%MSYS2_DIR%\usr\bin\bash -lc "cd /c/mill && out/dev/assembly/dest/mill.bat -i all main.test scalajslib.test")
   - if [%COMPILER%]==[cygwin] (
       SET "PATH=%JAVA_HOME%\bin;C:\%CYGWIN_DIR%\bin;C:\%CYGWIN_DIR%\usr\bin;%PATH%" &&
-      C:\%CYGWIN_DIR%\bin\bash -lc 'mkdir -p /usr/local/bin' &&
+      C:\%CYGWIN_DIR%\bin\bash -lc 'os.makeDir.all -p /usr/local/bin' &&
       C:\%CYGWIN_DIR%\bin\bash -lc "curl -Lo /usr/local/bin/mill %MILL_URL%" &&
       C:\%CYGWIN_DIR%\bin\bash -lc 'sed -i '"'"'0,/-cp "\$0"/{s/-cp "\$0"/-cp `cygpath -w "\$0"`/}; 0,/-cp "\$0"/{s/-cp "\$0"/-cp `cygpath -w "\$0"`/}'"'"' /usr/local/bin/mill' &&
       C:\%CYGWIN_DIR%\bin\bash -lc 'chmod +x /usr/local/bin/mill' &&
diff --git a/build.sc b/build.sc
index 969a3287..8e4b1b13 100755
--- a/build.sc
+++ b/build.sc
@@ -88,7 +88,7 @@ object main extends MillModule {
 
     def ivyDeps = Agg(
       // Keep synchronized with ammonite in Versions.scala
-      ivy"com.lihaoyi:::ammonite:1.3.3",
+      ivy"com.lihaoyi:::ammonite:1.4.0",
       // Necessary so we can share the JNA classes throughout the build process
       ivy"net.java.dev.jna:jna:4.5.0",
       ivy"net.java.dev.jna:jna-platform:4.5.0"
diff --git a/contrib/buildinfo/src/mill/contrib/BuildInfo.scala b/contrib/buildinfo/src/mill/contrib/BuildInfo.scala
index 0eb94a6d..9202fd95 100644
--- a/contrib/buildinfo/src/mill/contrib/BuildInfo.scala
+++ b/contrib/buildinfo/src/mill/contrib/BuildInfo.scala
@@ -1,6 +1,5 @@
 package mill.contrib
 
-import ammonite.ops.write
 import mill.T
 import mill.define.Target
 import mill.eval.PathRef
@@ -26,7 +25,7 @@ trait BuildInfo extends ScalaModule {
           case (name, value) => s"""  def ${name} = "${value}""""
         }
         .mkString("\n")
-    write(outputFile,
+    os.write(outputFile,
       s"""|${buildInfoPackageName.map(p => s"package ${p}").getOrElse("")}
           |object ${buildInfoObjectName} {
           |$internalMembers
diff --git a/contrib/buildinfo/test/src/mill/contrib/BuildInfoTests.scala b/contrib/buildinfo/test/src/mill/contrib/BuildInfoTests.scala
index e2147bac..05070985 100644
--- a/contrib/buildinfo/test/src/mill/contrib/BuildInfoTests.scala
+++ b/contrib/buildinfo/test/src/mill/contrib/BuildInfoTests.scala
@@ -1,6 +1,5 @@
 package mill.contrib
 
-import ammonite.ops._
 import java.util.jar.JarFile
 import mill._
 import mill.define.Target
@@ -43,16 +42,16 @@ object BuildInfoTests extends TestSuite {
     }
   }
 
-  val resourcePath = pwd / 'contrib / 'buildinfo / 'test / 'resources / "buildinfo"
+  val resourcePath = os.pwd / 'contrib / 'buildinfo / 'test / 'resources / "buildinfo"
 
-  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: Path = resourcePath)
+  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: os.Path = resourcePath)
                       (t: TestEvaluator => T)
                       (implicit tp: TestPath): T = {
     val eval = new TestEvaluator(m)
-    rm(m.millSourcePath)
-    rm(eval.outPath)
-    mkdir(m.millSourcePath / up)
-    cp(resourcePath, m.millSourcePath)
+    os.remove.all(m.millSourcePath)
+    os.remove.all(eval.outPath)
+    os.makeDir.all(m.millSourcePath / os.up)
+    os.copy(resourcePath, m.millSourcePath)
     t(eval)
   }
 
@@ -68,8 +67,8 @@ object BuildInfoTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(BuildInfo.buildInfo)
         assert(
           result.head.path == eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala" &&
-            exists(result.head.path) &&
-            read! result.head.path == expected
+            os.exists(result.head.path) &&
+            os.read(result.head.path) == expected
         )
       }
 
@@ -77,7 +76,7 @@ object BuildInfoTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(EmptyBuildInfo.buildInfo)
         assert(
           result.isEmpty &&
-            !exists(eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala")
+            !os.exists(eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala")
         )
       }
 
@@ -90,8 +89,8 @@ object BuildInfoTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(BuildInfoSettings.buildInfo)
         assert(
           result.head.path == eval.outPath / 'buildInfo / 'dest / "BuildInfo.scala" &&
-            exists(result.head.path) &&
-            read! result.head.path == expected
+            os.exists(result.head.path) &&
+            os.read(result.head.path) == expected
         )
       }
 
@@ -104,8 +103,8 @@ object BuildInfoTests extends TestSuite {
         val runResult = eval.outPath / "hello-mill"
         val Right((result, evalCount)) = eval.apply(BuildInfo.run(runResult.toString))
         assert(
-          exists(runResult),
-          read(runResult) == scalaVersionString)
+          os.exists(runResult),
+          os.read(runResult) == scalaVersionString)
       }
     }
   }
diff --git a/contrib/scalapblib/src/mill/contrib/scalapblib/ScalaPBWorker.scala b/contrib/scalapblib/src/mill/contrib/scalapblib/ScalaPBWorker.scala
index ea11a624..a1b345b4 100644
--- a/contrib/scalapblib/src/mill/contrib/scalapblib/ScalaPBWorker.scala
+++ b/contrib/scalapblib/src/mill/contrib/scalapblib/ScalaPBWorker.scala
@@ -5,15 +5,14 @@ import java.io.File
 import java.lang.reflect.Method
 import java.net.URLClassLoader
 
-import ammonite.ops.{Path, ls}
 import mill.eval.PathRef
 
 class ScalaPBWorker {
 
   private var scalaPBInstanceCache = Option.empty[(Long, ScalaPBWorkerApi)]
 
-  private def scalaPB(scalaPBClasspath: Agg[Path]) = {
-    val classloaderSig = scalaPBClasspath.map(p => p.toString().hashCode + p.mtime.toMillis).sum
+  private def scalaPB(scalaPBClasspath: Agg[os.Path]) = {
+    val classloaderSig = scalaPBClasspath.map(p => p.toString().hashCode + os.mtime(p)).sum
     scalaPBInstanceCache match {
       case Some((sig, instance)) if sig == classloaderSig => instance
       case _ =>
@@ -40,14 +39,14 @@ class ScalaPBWorker {
     }
   }
 
-  def compile(scalaPBClasspath: Agg[Path], scalaPBSources: Seq[Path], scalaPBOptions: String, dest: Path)
+  def compile(scalaPBClasspath: Agg[os.Path], scalaPBSources: Seq[os.Path], scalaPBOptions: String, dest: os.Path)
              (implicit ctx: mill.util.Ctx): mill.eval.Result[PathRef] = {
     val compiler = scalaPB(scalaPBClasspath)
 
-    def compileScalaPBDir(inputDir: Path) {
+    def compileScalaPBDir(inputDir: os.Path) {
       // ls throws if the path doesn't exist
       if (inputDir.toIO.exists) {
-        ls.rec(inputDir).filter(_.name.matches(".*.proto"))
+        os.walk(inputDir).filter(_.last.matches(".*.proto"))
           .foreach { proto =>
             compiler.compileScalaPB(proto.toIO, scalaPBOptions, dest.toIO)
           }
diff --git a/contrib/scalapblib/test/src/mill/contrib/scalapblib/TutorialTests.scala b/contrib/scalapblib/test/src/mill/contrib/scalapblib/TutorialTests.scala
index 8542d60e..65558f72 100644
--- a/contrib/scalapblib/test/src/mill/contrib/scalapblib/TutorialTests.scala
+++ b/contrib/scalapblib/test/src/mill/contrib/scalapblib/TutorialTests.scala
@@ -1,6 +1,5 @@
 package mill.contrib.scalapblib
 
-import ammonite.ops.{Path, cp, ls, mkdir, pwd, rm, _}
 import mill.eval.Result
 import mill.util.{TestEvaluator, TestUtil}
 import utest.framework.TestPath
@@ -9,7 +8,7 @@ import utest.{TestSuite, Tests, assert, _}
 object TutorialTests extends TestSuite {
 
   trait TutorialBase extends TestUtil.BaseModule {
-    override def millSourcePath: Path = TestUtil.getSrcPathBase() / millOuterCtx.enclosing.split('.')
+    override def millSourcePath: os.Path = TestUtil.getSrcPathBase() / millOuterCtx.enclosing.split('.')
   }
 
   trait TutorialModule extends ScalaPBModule {
@@ -25,24 +24,24 @@ object TutorialTests extends TestSuite {
     }
   }
 
-  val resourcePath: Path = pwd / 'contrib / 'scalapblib / 'test / 'protobuf / 'tutorial
+  val resourcePath: os.Path = os.pwd / 'contrib / 'scalapblib / 'test / 'protobuf / 'tutorial
 
-  def protobufOutPath(eval: TestEvaluator): Path =
+  def protobufOutPath(eval: TestEvaluator): os.Path =
     eval.outPath / 'core / 'compileScalaPB / 'dest / 'com / 'example / 'tutorial
 
   def workspaceTest[T](m: TestUtil.BaseModule)(t: TestEvaluator => T)
                       (implicit tp: TestPath): T = {
     val eval = new TestEvaluator(m)
-    rm(m.millSourcePath)
+    os.remove.all(m.millSourcePath)
     println(m.millSourcePath)
-    rm(eval.outPath)
+    os.remove.all(eval.outPath)
     println(eval.outPath)
-    mkdir(m.millSourcePath / 'core / 'protobuf)
-    cp(resourcePath, m.millSourcePath / 'core / 'protobuf / 'tutorial)
+    os.makeDir.all(m.millSourcePath / 'core / 'protobuf)
+    os.copy(resourcePath, m.millSourcePath / 'core / 'protobuf / 'tutorial)
     t(eval)
   }
 
-  def compiledSourcefiles: Seq[RelPath] = Seq[RelPath](
+  def compiledSourcefiles: Seq[os.RelPath] = Seq[os.RelPath](
     "AddressBook.scala",
     "Person.scala",
     "TutorialProto.scala"
@@ -67,7 +66,7 @@ object TutorialTests extends TestSuite {
 
         val outPath = protobufOutPath(eval)
 
-        val outputFiles = ls.rec(result.path).filter(_.isFile)
+        val outputFiles = os.walk(result.path).filter(os.isFile)
 
         val expectedSourcefiles = compiledSourcefiles.map(outPath / _)
 
@@ -92,7 +91,7 @@ object TutorialTests extends TestSuite {
 
       //   val outPath = protobufOutPath(eval)
 
-      //   val outputFiles = ls.rec(outPath).filter(_.isFile)
+      //   val outputFiles = os.walk(outPath).filter(_.isFile)
 
       //   val expectedSourcefiles = compiledSourcefiles.map(outPath / _)
 
diff --git a/contrib/tut/src/mill/contrib/tut/TutModule.scala b/contrib/tut/src/mill/contrib/tut/TutModule.scala
index f051a465..e51a8d7b 100644
--- a/contrib/tut/src/mill/contrib/tut/TutModule.scala
+++ b/contrib/tut/src/mill/contrib/tut/TutModule.scala
@@ -1,7 +1,6 @@
 package mill
 package contrib.tut
 
-import ammonite.ops._
 import coursier.MavenRepository
 import mill.scalalib._
 import scala.util.matching.Regex
@@ -51,7 +50,7 @@ trait TutModule extends ScalaModule {
     * A task which determines where the compiled documentation files will be placed. By default this is simply the Mill build's output folder for this task,
     * but this can be reconfigured so that documentation goes to the root of the module (e.g. `millSourcePath`) or to a dedicated folder (e.g. `millSourcePath / 'docs`)
     */
-  def tutTargetDirectory: T[Path] = T { T.ctx().dest }
+  def tutTargetDirectory: T[os.Path] = T { T.ctx().dest }
 
   /**
     * A task which determines what classpath is used when compiling documentation. By default this is configured to use the same inputs as the [[mill.contrib.tut.TutModule#runClasspath]],
@@ -115,18 +114,18 @@ trait TutModule extends ScalaModule {
   /**
     * Run Tut using the configuration specified in this module. The working directory used is the [[mill.contrib.tut.TutModule#millSourcePath]].
     */
-  def tut: T[CommandResult] = T {
+  def tut: T[os.CommandResult] = T {
     val in = tutSourceDirectory().head.path.toIO.getAbsolutePath
     val out = tutTargetDirectory().toIO.getAbsolutePath
     val re = tutNameFilter()
     val opts = tutScalacOptions()
     val pOpts = tutPluginJars().map(pathRef => "-Xplugin:" + pathRef.path.toIO.getAbsolutePath)
     val tutArgs = List(in, out, re.pattern.toString) ++ opts ++ pOpts
-    %%(
+    os.proc(
       'java,
       "-cp", tutClasspath().map(_.path.toIO.getAbsolutePath).mkString(java.io.File.pathSeparator),
       "tut.TutMain",
       tutArgs
-    )(wd = millSourcePath)
+    ).call(millSourcePath)
   }
 }
diff --git a/contrib/tut/test/src/mill/contrib/tut/TutTests.scala b/contrib/tut/test/src/mill/contrib/tut/TutTests.scala
index fd369eed..8168930f 100644
--- a/contrib/tut/test/src/mill/contrib/tut/TutTests.scala
+++ b/contrib/tut/test/src/mill/contrib/tut/TutTests.scala
@@ -1,7 +1,6 @@
 package mill.contrib
 package tut
 
-import ammonite.ops._
 import mill._
 import mill.eval.Result._
 import mill.scalalib._
@@ -29,17 +28,17 @@ object TutTests extends TestSuite {
     def scalacPluginIvyDeps = Agg(ivy"org.spire-math::kind-projector:0.9.8")
   }
 
-  val resourcePath = pwd / 'contrib / 'tut / 'test / 'tut
-  val resourcePathWithLibraries = pwd / 'contrib / 'tut / 'test / "tut-with-libraries"
+  val resourcePath = os.pwd / 'contrib / 'tut / 'test / 'tut
+  val resourcePathWithLibraries = os.pwd / 'contrib / 'tut / 'test / "tut-with-libraries"
 
-  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: Path = resourcePath)
+  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: os.Path = resourcePath)
                       (t: TestEvaluator => T)
                       (implicit tp: TestPath): T = {
     val eval = new TestEvaluator(m)
-    rm(m.millSourcePath)
-    rm(eval.outPath)
-    mkdir(m.millSourcePath)
-    cp(resourcePath, m.millSourcePath / 'tut)
+    os.remove.all(m.millSourcePath)
+    os.remove.all(eval.outPath)
+    os.makeDir.all(m.millSourcePath)
+    os.copy(resourcePath, m.millSourcePath / 'tut)
     t(eval)
   }
 
@@ -61,8 +60,8 @@ object TutTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(TutTest.tut)
 
         assert(
-          exists(expectedPath) &&
-            read! expectedPath == expected
+          os.exists(expectedPath) &&
+          os.read(expectedPath) == expected
         )
       }
 
@@ -84,9 +83,9 @@ object TutTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(TutCustomTest.tut)
 
         assert(
-          !exists(defaultPath) &&
-            exists(expectedPath) &&
-            read! expectedPath == expected
+          !os.exists(defaultPath) &&
+            os.exists(expectedPath) &&
+            os.read(expectedPath) == expected
         )
       }
 
@@ -115,8 +114,8 @@ object TutTests extends TestSuite {
         val Right(_) = eval.apply(TutLibrariesTest.tut)
 
         assert(
-          exists(expectedPath) &&
-            read! expectedPath == expected
+          os.exists(expectedPath) &&
+          os.read(expectedPath) == expected
         )
       }
     }
diff --git a/contrib/twirllib/src/mill/twirllib/TwirlWorker.scala b/contrib/twirllib/src/mill/twirllib/TwirlWorker.scala
index b73ed5dc..ce8175a6 100644
--- a/contrib/twirllib/src/mill/twirllib/TwirlWorker.scala
+++ b/contrib/twirllib/src/mill/twirllib/TwirlWorker.scala
@@ -5,7 +5,6 @@ import java.io.File
 import java.lang.reflect.Method
 import java.net.URLClassLoader
 
-import ammonite.ops.{Path, ls}
 import mill.eval.PathRef
 import mill.scalalib.CompilationResult
 
@@ -15,8 +14,8 @@ class TwirlWorker {
 
   private var twirlInstanceCache = Option.empty[(Long, TwirlWorkerApi)]
 
-  private def twirl(twirlClasspath: Agg[Path]) = {
-    val classloaderSig = twirlClasspath.map(p => p.toString().hashCode + p.mtime.toMillis).sum
+  private def twirl(twirlClasspath: Agg[os.Path]) = {
+    val classloaderSig = twirlClasspath.map(p => p.toString().hashCode + os.mtime(p)).sum
     twirlInstanceCache match {
       case Some((sig, instance)) if sig == classloaderSig => instance
       case _ =>
@@ -61,9 +60,9 @@ class TwirlWorker {
     }
   }
 
-  def compile(twirlClasspath: Agg[Path],
-              sourceDirectories: Seq[Path],
-              dest: Path,
+  def compile(twirlClasspath: Agg[os.Path],
+              sourceDirectories: Seq[os.Path],
+              dest: os.Path,
               additionalImports: Seq[String],
               constructorAnnotations: Seq[String],
               codec: Codec,
@@ -71,10 +70,10 @@ class TwirlWorker {
              (implicit ctx: mill.util.Ctx): mill.eval.Result[CompilationResult] = {
     val compiler = twirl(twirlClasspath)
 
-    def compileTwirlDir(inputDir: Path) {
-      ls.rec(inputDir).filter(_.name.matches(".*.scala.(html|xml|js|txt)"))
+    def compileTwirlDir(inputDir: os.Path) {
+      os.walk(inputDir).filter(_.last.matches(".*.scala.(html|xml|js|txt)"))
         .foreach { template =>
-          val extFormat = twirlExtensionFormat(template.name)
+          val extFormat = twirlExtensionFormat(template.last)
           compiler.compileTwirl(template.toIO,
             inputDir.toIO,
             dest.toIO,
diff --git a/contrib/twirllib/test/src/mill/twirllib/HelloWorldTests.scala b/contrib/twirllib/test/src/mill/twirllib/HelloWorldTests.scala
index 8ef6ee3e..f14a607b 100644
--- a/contrib/twirllib/test/src/mill/twirllib/HelloWorldTests.scala
+++ b/contrib/twirllib/test/src/mill/twirllib/HelloWorldTests.scala
@@ -1,6 +1,5 @@
 package mill.twirllib
 
-import ammonite.ops.{Path, cp, ls, mkdir, pwd, rm, _}
 import mill.util.{TestEvaluator, TestUtil}
 import utest.framework.TestPath
 import utest.{TestSuite, Tests, assert, _}
@@ -8,7 +7,7 @@ import utest.{TestSuite, Tests, assert, _}
 object HelloWorldTests extends TestSuite {
 
   trait HelloBase extends TestUtil.BaseModule {
-    override def millSourcePath: Path = TestUtil.getSrcPathBase() / millOuterCtx.enclosing.split('.')
+    override def millSourcePath: os.Path = TestUtil.getSrcPathBase() / millOuterCtx.enclosing.split('.')
   }
 
   trait HelloWorldModule extends mill.twirllib.TwirlModule {
@@ -22,20 +21,20 @@ object HelloWorldTests extends TestSuite {
     }
   }
 
-  val resourcePath: Path = pwd / 'contrib / 'twirllib / 'test / 'resources / "hello-world"
+  val resourcePath: os.Path = os.pwd / 'contrib / 'twirllib / 'test / 'resources / "hello-world"
 
-  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: Path = resourcePath)
+  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: os.Path = resourcePath)
                       (t: TestEvaluator => T)
                       (implicit tp: TestPath): T = {
     val eval = new TestEvaluator(m)
-    rm(m.millSourcePath)
-    rm(eval.outPath)
-    mkdir(m.millSourcePath / up)
-    cp(resourcePath, m.millSourcePath)
+    os.remove.all(m.millSourcePath)
+    os.remove.all(eval.outPath)
+    os.makeDir.all(m.millSourcePath / os.up)
+    os.copy(resourcePath, m.millSourcePath)
     t(eval)
   }
 
-  def compileClassfiles: Seq[RelPath] = Seq[RelPath](
+  def compileClassfiles: Seq[os.RelPath] = Seq[os.RelPath](
     "hello.template.scala"
   )
 
@@ -54,7 +53,7 @@ object HelloWorldTests extends TestSuite {
     'compileTwirl - workspaceTest(HelloWorld) { eval =>
       val Right((result, evalCount)) = eval.apply(HelloWorld.core.compileTwirl)
 
-      val outputFiles = ls.rec(result.classes.path)
+      val outputFiles = os.walk(result.classes.path)
       val expectedClassfiles = compileClassfiles.map(
         eval.outPath / 'core / 'compileTwirl / 'dest / 'html / _
       )
diff --git a/docs/build.sc b/docs/build.sc
index 42a4f141..661aa462 100644
--- a/docs/build.sc
+++ b/docs/build.sc
@@ -4,7 +4,7 @@ import $file.pageStyles, pageStyles._
 import $file.pages, pages._
 import scalatags.Text.all._
 
-import ammonite.ops._
+
 import collection.JavaConverters._
 import org.pegdown.{PegDownProcessor, ToHtmlSerializer, LinkRenderer, Extensions}
 import org.pegdown.ast.{VerbatimNode, ExpImageNode, HeaderNode, TextNode, SimpleNode, TableNode}
@@ -134,18 +134,18 @@ def formatRssDate(date: java.time.LocalDate) = {
 @main
 def main(publish: Boolean = false) = {
 
-  rm! targetFolder
+  os.remove.all! targetFolder
 
-  mkdir! targetFolder/'page
+  os.makeDir.all! targetFolder/'page
   for(otherFile <- otherFiles){
-    cp(otherFile, targetFolder/'page/(otherFile relativeTo postsFolder))
+    os.copy(otherFile, targetFolder/'page/(otherFile relativeTo postsFolder))
   }
 
-  cp(pwd/"favicon.png", targetFolder/"favicon.ico")
-  cp(pwd/"logo-white.svg", targetFolder/"logo-white.svg")
-  cp(pwd/"VisualizeCompile.svg", targetFolder/"VisualizeCompile.svg")
-  cp(pwd/"VisualizeCore.svg", targetFolder/"VisualizeCore.svg")
-  cp(pwd/"VisualizePlan.svg", targetFolder/"VisualizePlan.svg")
+  os.copy(pwd/"favicon.png", targetFolder/"favicon.ico")
+  os.copy(pwd/"logo-white.svg", targetFolder/"logo-white.svg")
+  os.copy(pwd/"VisualizeCompile.svg", targetFolder/"VisualizeCompile.svg")
+  os.copy(pwd/"VisualizeCore.svg", targetFolder/"VisualizeCore.svg")
+  os.copy(pwd/"VisualizePlan.svg", targetFolder/"VisualizePlan.svg")
 
   %('zip, "-r", targetFolder/"example-1.zip", "example-1")(pwd)
   %('zip, "-r", targetFolder/"example-2.zip", "example-2")(pwd)
@@ -171,7 +171,7 @@ def main(publish: Boolean = false) = {
     )
 
 
-    write(
+    os.write(
       if (i == 0) targetFolder / "index.html"
       else targetFolder/'page/s"${sanitize(post.name)}.html",
       postContent(
diff --git a/docs/logo.sc b/docs/logo.sc
index 5d8cee3b..3464f9a9 100644
--- a/docs/logo.sc
+++ b/docs/logo.sc
@@ -2,7 +2,7 @@ import $ivy.`com.lihaoyi::scalatags:0.6.7`
 import scalatags.Text.implicits._
 import scalatags.Text.svgTags._
 import scalatags.Text.svgAttrs._
-import ammonite.ops._
+
 
 val svgWidth = 24
 val svgHeight = 24
diff --git a/docs/pages/2 - Configuring Mill.md b/docs/pages/2 - Configuring Mill.md
index 989272dd..f5a4a24e 100644
--- a/docs/pages/2 - Configuring Mill.md
+++ b/docs/pages/2 - Configuring Mill.md
@@ -291,8 +291,8 @@ object foo extends ScalaModule {
 }
 
 def lineCount = T {
-  import ammonite.ops._
-  foo.sources().flatMap(ref => ls.rec(ref.path)).filter(_.isFile).flatMap(read.lines).size
+  
+  foo.sources().flatMap(ref => os.walk(ref.path)).filter(_.isFile).flatMap(read.lines).size
 }
 
 def printLineCount() = T.command {
diff --git a/docs/pages/4 - Tasks.md b/docs/pages/4 - Tasks.md
index e8a1c94c..e69ae662 100644
--- a/docs/pages/4 - Tasks.md
+++ b/docs/pages/4 - Tasks.md
@@ -5,22 +5,22 @@ for building Scala.
 The following is a simple self-contained example using Mill to compile Java:
 
 ```scala
-import ammonite.ops._, mill._
+, mill._
 
 // sourceRoot -> allSources -> classFiles
 //                                |
 //                                v
 //           resourceRoot ---->  jar
 
-def sourceRoot = T.sources { pwd / 'src }
+def sourceRoot = T.sources { os.pwd / 'src }
 
-def resourceRoot = T.sources { pwd / 'resources }
+def resourceRoot = T.sources { os.pwd / 'resources }
 
-def allSources = T { sourceRoot().flatMap(p => ls.rec(p.path)).map(PathRef(_)) }
+def allSources = T { sourceRoot().flatMap(p => os.walk(p.path)).map(PathRef(_)) }
 
 def classFiles = T { 
-  mkdir(T.ctx().dest)
-  import ammonite.ops._
+  os.makeDir.all(T.ctx().dest)
+  
   %("javac", sources().map(_.path.toString()), "-d", T.ctx().dest)(wd = T.ctx().dest)
   PathRef(T.ctx().dest) 
 }
@@ -28,7 +28,7 @@ def classFiles = T {
 def jar = T { Jvm.createJar(Loose.Agg(classFiles().path) ++ resourceRoot().map(_.path)) }
 
 def run(mainClsName: String) = T.command {
-  %%('java, "-cp", classFiles().path, mainClsName)
+  os.proc('java, "-cp", classFiles().path, mainClsName).call()
 }
 ```
 
@@ -78,7 +78,7 @@ There are three primary kinds of *Tasks* that you should care about:
 ### Targets
 
 ```scala
-def allSources = T { ls.rec(sourceRoot().path).map(PathRef(_)) }
+def allSources = T { os.walk(sourceRoot().path).map(PathRef(_)) }
 ```
 
 `Target`s are defined using the `def foo = T {...}` syntax, and dependencies on
@@ -127,7 +127,7 @@ within a `Module` body.
 ### Sources
 
 ```scala
-def sourceRootPath = pwd / 'src
+def sourceRootPath = os.pwd / 'src
 
 def sourceRoots = T.sources { sourceRootPath }
 ```
@@ -143,7 +143,7 @@ override-and-extend source lists the same way you would any other `T {...}`
 definition:
 
 ```scala
-def additionalSources = T.sources { pwd / 'additionalSources }
+def additionalSources = T.sources { os.pwd / 'additionalSources }
 def sourceRoots = T.sources { super.sourceRoots() ++ additionalSources() }
 ```
 
@@ -151,7 +151,7 @@ def sourceRoots = T.sources { super.sourceRoots() ++ additionalSources() }
 
 ```scala
 def run(mainClsName: String) = T.command {
-  %%('java, "-cp", classFiles().path, mainClsName)
+  os.proc('java, "-cp", classFiles().path, mainClsName).call()
 }
 ```
 
@@ -288,7 +288,7 @@ affect your build. For example, if I have a [Target](#targets) `bar` that makes
 use of the current git version:
 
 ```scala
-def bar = T { ... %%("git", "rev-parse", "HEAD").out.string ... }
+def bar = T { ... os.proc("git", "rev-parse", "HEAD").call().out.string ... }
 ```
 
 `bar` will not know that `git rev-parse` can change, and will
@@ -299,7 +299,7 @@ be out of date!
 To fix this, you can wrap your `git rev-parse HEAD` in a `T.input`:
 
 ```scala
-def foo = T.input { %%("git", "rev-parse", "HEAD").out.string }
+def foo = T.input { os.proc("git", "rev-parse", "HEAD").call().out.string }
 def bar = T { ... foo() ... }
 ```
 
diff --git a/docs/pages/9 - Contrib Modules.md b/docs/pages/9 - Contrib Modules.md
index cd02f2c2..e071d59c 100644
--- a/docs/pages/9 - Contrib Modules.md
+++ b/docs/pages/9 - Contrib Modules.md
@@ -244,7 +244,7 @@ object app extends ScalaModule with TwirlModule {
   def twirlVersion = "1.3.15"
   override def generatedSources = T{
     val classes = compileTwirl().classes
-    Seq(classes.copy(path = classes.path / up)) // we just move one dir up
+    Seq(classes.copy(path = classes.path / os.up)) // we just move one dir up
   }
 }
 ``` 
diff --git a/integration/test/resources/ammonite/build.sc b/integration/test/resources/ammonite/build.sc
index c26d5050..34f80825 100644
--- a/integration/test/resources/ammonite/build.sc
+++ b/integration/test/resources/ammonite/build.sc
@@ -65,8 +65,8 @@ object amm extends Cross[MainModule](fullCrossScalaVersions:_*){
     )
 
     def generatedSources = T{
-      import ammonite.ops._
-      cp(build.millSourcePath/'project/"Constants.scala", T.ctx().dest/"Constants.scala")
+
+      os.copy(build.millSourcePath/'project/"Constants.scala", T.ctx().dest/"Constants.scala")
       Seq(PathRef(T.ctx().dest))
     }
   }
diff --git a/integration/test/resources/jawn/build.sc b/integration/test/resources/jawn/build.sc
index deb9731a..8b58efc7 100644
--- a/integration/test/resources/jawn/build.sc
+++ b/integration/test/resources/jawn/build.sc
@@ -1,10 +1,9 @@
 import mill.scalalib
 import mill.Cross
 import mill.scalalib.{Dep, TestModule, DepSyntax, Lib}
-import ammonite.ops.up
 object jawn extends Cross[JawnModule]("2.10.6", "2.11.11", "2.12.3")
 class JawnModule(crossVersion: String) extends mill.Module{
-  override def millSourcePath = super.millSourcePath / up / up
+  override def millSourcePath = super.millSourcePath / os.up / os.up
 
   trait JawnModule extends scalalib.SbtModule{
     def scalaVersion = crossVersion
@@ -53,7 +52,7 @@ class JawnModule(crossVersion: String) extends mill.Module{
 
     object rojoma extends Support(ivy"com.rojoma::rojoma-json:2.4.3")
     object rojomaV3 extends Support(ivy"com.rojoma::rojoma-json-v3:3.7.2"){
-      override def millSourcePath = super.millSourcePath / up / "rojoma-v3"
+      override def millSourcePath = super.millSourcePath / os.up / "rojoma-v3"
     }
     object spray extends Support(ivy"io.spray::spray-json:1.3.3")
   }
diff --git a/integration/test/resources/play-json/build.sc b/integration/test/resources/play-json/build.sc
index d4557011..54e63d65 100644
--- a/integration/test/resources/play-json/build.sc
+++ b/integration/test/resources/play-json/build.sc
@@ -10,7 +10,7 @@ import jmh.Jmh
 import headers.Headers
 import com.typesafe.tools.mima.core._
 
-import ammonite.ops._
+
 import mill.define.Task
 
 val ScalaVersions = Seq("2.10.7", "2.11.12", "2.12.4", "2.13.0-M3")
@@ -52,7 +52,7 @@ trait PlayJsonModule extends BaseModule with PublishModule with MiMa {
 
 abstract class PlayJson(val platformSegment: String) extends PlayJsonModule {
   def crossScalaVersion: String
-  def millSourcePath = pwd /  "play-json"
+  def millSourcePath = os.pwd /  "play-json"
   def artifactName = "play-json"
 
   def sources = T.sources(
@@ -90,10 +90,10 @@ abstract class PlayJson(val platformSegment: String) extends PlayJsonModule {
   )
 
   def generatedSources = T {
-    import ammonite.ops._
+
 
     val dir = T.ctx().dest
-    mkdir(dir / "play-json")
+    os.makeDir.all(dir / "play-json")
     val file = dir / "play-json" / "Generated.scala"
 
     val (writes, reads) = (1 to 22).map { i =>
@@ -126,7 +126,7 @@ abstract class PlayJson(val platformSegment: String) extends PlayJsonModule {
         """)
     }.unzip
 
-    write(file, s"""
+    os.write(file, s"""
         package play.api.libs.json
 
         trait GeneratedReads {
@@ -168,7 +168,11 @@ class PlayJsonJvm(val crossScalaVersion: String) extends PlayJson("jvm") {
       )
 
     def sources = {
-      val docSpecs = ls.rec(millSourcePath / up / "docs" / "manual" / "working" / "scalaGuide").filter(_.isDir).filter(_.last=="code").map(PathRef(_))
+      val docSpecs = os.walk(millSourcePath / os.up / "docs" / "manual" / "working" / "scalaGuide")
+        .filter(os.isDir)
+        .filter(_.last=="code")
+        .map(PathRef(_))
+
       T.sources(
         docSpecs ++
         Seq(
@@ -213,7 +217,7 @@ class PlayJsonJs(val crossScalaVersion: String) extends PlayJson("js") with Scal
 }
 
 trait PlayFunctional extends PlayJsonModule {
-  def millSourcePath = pwd / "play-functional"
+  def millSourcePath = os.pwd / "play-functional"
   def artifactName = "play-functional"
 }
 
@@ -229,7 +233,7 @@ object playJoda extends Cross[PlayJoda](ScalaVersions:_*)
 class PlayJoda(val crossScalaVersion: String) extends PlayJsonModule {
   def moduleDeps = Seq(playJsonJvm(crossScalaVersion))
 
-  def millSourcePath = pwd / "play-json-joda"
+  def millSourcePath = os.pwd / "play-json-joda"
   def artifactName = "play-json-joda"
 
   def ivyDeps = Agg(
@@ -250,7 +254,7 @@ object benchmarks extends Cross[Benchmarks](ScalaVersions:_*)
 class Benchmarks(val crossScalaVersion: String) extends BaseModule with Jmh {
   def moduleDeps = Seq(playJsonJvm(crossScalaVersion))
 
-  def millSourcePath = pwd / "benchmarks"
+  def millSourcePath = os.pwd / "benchmarks"
 }
 
 // TODO: we should have a way to "take all modules in this build"
@@ -322,7 +326,7 @@ def validateCode() = T.command {
   */
 object release extends Module {
 
-  implicit val wd = pwd
+  implicit val wd = os.pwd
 
   val versionFile = wd / "version.sc"
 
@@ -345,27 +349,27 @@ object release extends Module {
   def setReleaseVersion = T {
     T.ctx.log.info(s"Setting release version to ${releaseVersion}")
 
-    write.over(
+    os.write.over(
       versionFile,
       s"""def current = "${releaseVersion}"
          |
        """.stripMargin
     )
 
-    %%("git", "commit", "-am", s"Setting release version to ${releaseVersion}")
-    %%("git", "tag", s"$releaseVersion")
+    os.proc("git", "commit", "-am", s"Setting release version to ${releaseVersion}").call()
+    os.proc("git", "tag", s"$releaseVersion").call()
   }
 
   def setNextVersion = T {
     T.ctx.log.info(s"Setting next version to ${nextVersion}")
 
-    write.over(
+    os.write.over(
       versionFile,
       s"""def current = "${nextVersion}""""
     )
 
-    %%("git", "commit", "-am", s"Setting next version to ${nextVersion}")
-    %%("git", "push", "origin", "master", "--tags")
+    os.proc("git", "commit", "-am", s"Setting next version to ${nextVersion}").call()
+    os.proc("git", "push", "origin", "master", "--tags").call()
   }
 
 }
diff --git a/integration/test/resources/play-json/headers.sc b/integration/test/resources/play-json/headers.sc
index a66eaedd..9737cb3d 100644
--- a/integration/test/resources/play-json/headers.sc
+++ b/integration/test/resources/play-json/headers.sc
@@ -1,6 +1,6 @@
 import $ivy.`com.github.rockjam::license-headers:0.0.1`
 
-import ammonite.ops._
+
 import mill._, scalalib._
 import mill.eval.PathRef
 import de.heikoseeberger.sbtheader.{CommentStyle, FileType, HeaderCreator, License}
@@ -24,7 +24,7 @@ trait Headers extends ScalaModule {
 
     val updatedFiles = withoutHeaders.map {
       case (file, updated) =>
-        write.over(file, updated)
+        os.write.over(file, updated)
         file
     }
 
@@ -47,15 +47,15 @@ trait Headers extends ScalaModule {
 
   private def filesWithoutHeaders(input: Seq[PathRef]) = {
     for {
-      ref <- input if exists(ref.path)
-      file <- ls.rec(ref.path) if file.isFile
+      ref <- input if os.exists(ref.path)
+      file <- os.walk(ref.path) if os.isFile(file)
       (fileType, commentStyle) <- headerMappings.get(file.ext)
       updatedContent <- HeaderCreator(
         fileType,
         commentStyle,
         license,
         log = _ => (),
-        read.getInputStream(file)
+        os.read.inputStream(file)
       ).createText
     } yield file -> updatedContent
   }
diff --git a/integration/test/resources/play-json/jmh.sc b/integration/test/resources/play-json/jmh.sc
index 76ed43fc..3c2c8411 100644
--- a/integration/test/resources/play-json/jmh.sc
+++ b/integration/test/resources/play-json/jmh.sc
@@ -1,4 +1,4 @@
-import ammonite.ops._
+
 import mill._, scalalib._, modules._
 
 trait Jmh extends ScalaModule {
@@ -19,13 +19,13 @@ trait Jmh extends ScalaModule {
   def compileGeneratedSources = T {
     val dest = T.ctx.dest
     val (sourcesDir, _) = generateBenchmarkSources()
-    val sources = ls.rec(sourcesDir).filter(_.isFile)
-    %%("javac",
+    val sources = os.walk(sourcesDir).filter(os.isFile)
+    os.proc("javac",
        sources.map(_.toString),
        "-cp",
        (runClasspath() ++ generatorDeps()).map(_.path.toString).mkString(":"),
        "-d",
-       dest)(wd = dest)
+       dest).call(dest)
     PathRef(dest)
   }
 
@@ -36,10 +36,10 @@ trait Jmh extends ScalaModule {
     val sourcesDir = dest / 'jmh_sources
     val resourcesDir = dest / 'jmh_resources
 
-    rm(sourcesDir)
-    mkdir(sourcesDir)
-    rm(resourcesDir)
-    mkdir(resourcesDir)
+    os.remove.all(sourcesDir)
+    os.makeDir.all(sourcesDir)
+    os.remove.all(resourcesDir)
+    os.makeDir.all(resourcesDir)
 
     Jvm.subprocess(
       "org.openjdk.jmh.generators.bytecode.JmhBytecodeGenerator",
diff --git a/integration/test/resources/play-json/mima.sc b/integration/test/resources/play-json/mima.sc
index 3902f2c7..baca333c 100644
--- a/integration/test/resources/play-json/mima.sc
+++ b/integration/test/resources/play-json/mima.sc
@@ -1,4 +1,4 @@
-import ammonite.ops._
+
 import $ivy.`com.typesafe::mima-reporter:0.1.18`
 import com.typesafe.tools.mima.lib.MiMaLib
 import com.typesafe.tools.mima.core._
@@ -34,7 +34,7 @@ trait MiMa extends ScalaModule with PublishModule {
       com.typesafe.tools.mima.core.Config.setup("sbt-mima-plugin", Array.empty)
       val cpstring = classpath
         .map(_.path)
-        .filter(exists)
+        .filter(os.exists)
         .mkString(System.getProperty("path.separator"))
       new MiMaLib(
         com.typesafe.tools.mima.core.reporterClassPath(cpstring)
diff --git a/integration/test/resources/play-json/reformat.sc b/integration/test/resources/play-json/reformat.sc
index c44b2f97..3127bc5d 100644
--- a/integration/test/resources/play-json/reformat.sc
+++ b/integration/test/resources/play-json/reformat.sc
@@ -1,7 +1,7 @@
 import $ivy.`org.scalariform::scalariform:0.2.5`
 
 import mill._, scalalib._
-import ammonite.ops._
+
 import scalariform.formatter._
 import scalariform.formatter.preferences._
 import scalariform.parser.ScalaParserException
@@ -25,11 +25,11 @@ trait Scalariform extends ScalaModule {
     files.map { path =>
       try {
         val formatted = ScalaFormatter.format(
-          read(path),
+          os.read(path),
           playJsonPreferences,
           scalaVersion = scalaVersion()
         )
-        write.over(path, formatted)
+        os.write.over(path, formatted)
       } catch {
         case ex: ScalaParserException =>
           T.ctx.log.error(s"Failed to format file: ${path}. Error: ${ex.getMessage}")
@@ -41,7 +41,7 @@ trait Scalariform extends ScalaModule {
   def checkCodeFormat() = T.command {
     filesToFormat(sources()).foreach { path =>
       try {
-        val input = read(path)
+        val input = os.read(path)
         val formatted = ScalaFormatter.format(
           input,
           playJsonPreferences,
@@ -63,8 +63,8 @@ trait Scalariform extends ScalaModule {
 
   private def filesToFormat(sources: Seq[PathRef]) = {
     for {
-      pathRef <- sources if exists(pathRef.path)
-      file <- ls.rec(pathRef.path) if file.isFile && file.ext == "scala"
+      pathRef <- sources if os.exists(pathRef.path)
+      file <- os.walk(pathRef.path) if os.isFile(file) && file.ext == "scala"
     } yield file
   }
 
diff --git a/integration/test/resources/play-json/release.sh b/integration/test/resources/play-json/release.sh
index 009300a0..6efe80ce 100755
--- a/integration/test/resources/play-json/release.sh
+++ b/integration/test/resources/play-json/release.sh
@@ -2,7 +2,7 @@
 
 set -eux
 
-rm -rf out
+os.remove.all -rf out
 mill __.test
 mill release.setReleaseVersion
 mill mill.scalalib.PublishModule/publishAll \
diff --git a/integration/test/resources/upickle/build.sc b/integration/test/resources/upickle/build.sc
index 1f5f2bed..86552d9d 100644
--- a/integration/test/resources/upickle/build.sc
+++ b/integration/test/resources/upickle/build.sc
@@ -43,7 +43,7 @@ trait UpickleModule extends CrossSbtModule with PublishModule{
   def generatedSources = T{
     val dir = T.ctx().dest
     val file = dir / "upickle" / "Generated.scala"
-    ammonite.ops.mkdir(dir / "upickle")
+    os.makeDir.all(dir / "upickle")
     val tuplesAndCases = (1 to 22).map{ i =>
       def commaSeparated(s: Int => String) = (1 to i).map(s).mkString(", ")
       val writerTypes = commaSeparated(j => s"T$j: Writer")
diff --git a/integration/test/src/mill/integration/AcyclicTests.scala b/integration/test/src/mill/integration/AcyclicTests.scala
index c117f862..145c106d 100644
--- a/integration/test/src/mill/integration/AcyclicTests.scala
+++ b/integration/test/src/mill/integration/AcyclicTests.scala
@@ -1,6 +1,5 @@
 package mill.integration
 
-import ammonite.ops._
 import utest._
 
 class AcyclicTests(fork: Boolean)
@@ -13,11 +12,11 @@ class AcyclicTests(fork: Boolean)
 
       assert(
         firstCompile,
-        ls.rec(workspacePath).exists(_.last == "GraphAnalysis.class"),
-        ls.rec(workspacePath).exists(_.last == "PluginPhase.class")
+        os.walk(workspacePath).exists(_.last == "GraphAnalysis.class"),
+        os.walk(workspacePath).exists(_.last == "PluginPhase.class")
       )
-      for(scalaFile <- ls.rec(workspacePath).filter(_.ext == "scala")){
-        write.append(scalaFile, "\n}")
+      for(scalaFile <- os.walk(workspacePath).filter(_.ext == "scala")){
+        os.write.append(scalaFile, "\n}")
       }
 
       val brokenCompile = eval(s"acyclic[$scalaVersion].compile")
diff --git a/integration/test/src/mill/integration/AmmoniteTests.scala b/integration/test/src/mill/integration/AmmoniteTests.scala
index 3f04e84d..2f2c648d 100644
--- a/integration/test/src/mill/integration/AmmoniteTests.scala
+++ b/integration/test/src/mill/integration/AmmoniteTests.scala
@@ -1,6 +1,5 @@
 package mill.integration
 
-import ammonite.ops._
 import utest._
 
 class AmmoniteTests(fork: Boolean)
@@ -25,8 +24,8 @@ class AmmoniteTests(fork: Boolean)
 
       assert(
         compileResult,
-        ls.rec(workspacePath / 'out / 'integration / scalaVersion / 'test / 'compile)
-          .exists(_.name == "ErrorTruncationTests.class")
+        os.walk(workspacePath / 'out / 'integration / scalaVersion / 'test / 'compile)
+          .exists(_.last == "ErrorTruncationTests.class")
       )
     }
 
diff --git a/integration/test/src/mill/integration/BetterFilesTests.scala b/integration/test/src/mill/integration/BetterFilesTests.scala
index 4f3116f7..bdbaa2e3 100644
--- a/integration/test/src/mill/integration/BetterFilesTests.scala
+++ b/integration/test/src/mill/integration/BetterFilesTests.scala
@@ -1,6 +1,5 @@
 package mill.integration
 
-import ammonite.ops._
 import utest._
 
 class BetterFilesTests(fork: Boolean)
@@ -17,8 +16,8 @@ class BetterFilesTests(fork: Boolean)
       assert(coreTestMeta.contains("better.files.FileSpec"))
       assert(coreTestMeta.contains("files should handle BOM"))
 
-      for(scalaFile <- ls.rec(workspacePath).filter(_.ext == "scala")){
-        write.append(scalaFile, "\n}")
+      for(scalaFile <- os.walk(workspacePath).filter(_.ext == "scala")){
+        os.write.append(scalaFile, "\n}")
       }
       assert(!eval("akka.test"))
     }
diff --git a/integration/test/src/mill/integration/DocAnnotationsTests.scala b/integration/test/src/mill/integration/DocAnnotationsTests.scala
index 75579689..4d7ef11b 100644
--- a/integration/test/src/mill/integration/DocAnnotationsTests.scala
+++ b/integration/test/src/mill/integration/DocAnnotationsTests.scala
@@ -1,12 +1,11 @@
 package mill.integration
 
-import ammonite.ops.{Path, pwd}
 import mill.util.ScriptTestSuite
 import utest._
 
 class DocAnnotationsTests(fork: Boolean) extends ScriptTestSuite(fork) {
   def workspaceSlug: String = "docannotations"
-  def scriptSourcePath: Path = pwd / 'integration / 'test / 'resources / workspaceSlug
+  def scriptSourcePath: os.Path = os.pwd / 'integration / 'test / 'resources / workspaceSlug
   val tests = Tests{
     initWorkspace()
     'test - {
diff --git a/integration/test/src/mill/integration/IntegrationTestSuite.scala b/integration/test/src/mill/integration/IntegrationTestSuite.scala
index 721557c0..ca041eea 100644
--- a/integration/test/src/mill/integration/IntegrationTestSuite.scala
+++ b/integration/test/src/mill/integration/IntegrationTestSuite.scala
@@ -1,29 +1,28 @@
 package mill.integration
 
-import ammonite.ops._
 import mill.util.ScriptTestSuite
 import utest._
 
 abstract class IntegrationTestSuite(repoKey: String, val workspaceSlug: String, fork: Boolean)
   extends ScriptTestSuite(fork){
-  val buildFilePath = pwd / 'integration / 'test / 'resources / workspaceSlug
+  val buildFilePath = os.pwd / 'integration / 'test / 'resources / workspaceSlug
   def scriptSourcePath = {
     // The unzipped git repo snapshots we get from github come with a
     // wrapper-folder inside the zip file, so copy the wrapper folder to the
     // destination instead of the folder containing the wrapper.
 
     val path = sys.props(repoKey)
-    val Seq(wrapper) = ls(Path(path))
+    val Seq(wrapper) = os.list(os.Path(path))
     wrapper
   }
 
-  def buildFiles: Seq[Path] = ls.rec(buildFilePath)
+  def buildFiles: Seq[os.Path] = os.walk(buildFilePath)
 
   override def initWorkspace() = {
     super.initWorkspace()
     buildFiles.foreach { file =>
-      cp.over(file, workspacePath / file.name)
+      os.copy.over(file, workspacePath / file.last)
     }
-    assert(!ls.rec(workspacePath).exists(_.ext == "class"))
+    assert(!os.walk(workspacePath).exists(_.ext == "class"))
   }
 }
diff --git a/integration/test/src/mill/integration/JawnTests.scala b/integration/test/src/mill/integration/JawnTests.scala
index da584e01..eafd1009 100644
--- a/integration/test/src/mill/integration/JawnTests.scala
+++ b/integration/test/src/mill/integration/JawnTests.scala
@@ -1,6 +1,5 @@
 package mill.integration
 
-import ammonite.ops._
 import utest._
 
 class JawnTests(fork: Boolean)
@@ -13,12 +12,12 @@ class JawnTests(fork: Boolean)
 
       assert(
         firstCompile,
-        ls.rec(workspacePath).exists(_.last == "AsyncParser.class"),
-        ls.rec(workspacePath).exists(_.last == "CharBuilderSpec.class")
+        os.walk(workspacePath).exists(_.last == "AsyncParser.class"),
+        os.walk(workspacePath).exists(_.last == "CharBuilderSpec.class")
       )
 
-      for(scalaFile <- ls.rec(workspacePath).filter(_.ext == "scala")){
-        write.append(scalaFile, "\n}")
+      for(scalaFile <- os.walk(workspacePath).filter(_.ext == "scala")){
+        os.write.append(scalaFile, "\n}")
       }
 
       val brokenCompile = eval(s"jawn[$scalaVersion].parser.test")
diff --git a/integration/test/src/mill/integration/PlayJsonTests.scala b/integration/test/src/mill/integration/PlayJsonTests.scala
index c78a256e..262dcb36 100644
--- a/integration/test/src/mill/integration/PlayJsonTests.scala
+++ b/integration/test/src/mill/integration/PlayJsonTests.scala
@@ -1,12 +1,12 @@
 package mill.integration
 
-import ammonite.ops._
+
 import utest._
 
 class PlayJsonTests(fork: Boolean) extends IntegrationTestSuite("MILL_PLAY_JSON_REPO", "play-json", fork) {
 
-  override def buildFiles: Seq[Path] = {
-    ls(buildFilePath).filter(_.ext == "sc")
+  override def buildFiles: Seq[os.Path] = {
+    os.list(buildFilePath).filter(_.ext == "sc")
   }
 
   val tests = Tests{
diff --git a/integration/test/src/mill/integration/UpickleTests.scala b/integration/test/src/mill/integration/UpickleTests.scala
index 1b83c60f..133188d3 100644
--- a/integration/test/src/mill/integration/UpickleTests.scala
+++ b/integration/test/src/mill/integration/UpickleTests.scala
@@ -1,6 +1,5 @@
 package mill.integration
 
-import ammonite.ops._
 import utest._
 
 class UpickleTests(fork: Boolean) extends IntegrationTestSuite("MILL_UPICKLE_REPO", "upickle", fork) {
diff --git a/main/core/src/mill/define/BaseModule.scala b/main/core/src/mill/define/BaseModule.scala
index 03bdeccc..cd79f73e 100644
--- a/main/core/src/mill/define/BaseModule.scala
+++ b/main/core/src/mill/define/BaseModule.scala
@@ -1,12 +1,11 @@
 package mill.define
 
-import ammonite.ops.Path
 
 object BaseModule{
   case class Implicit(value: BaseModule)
 }
 
-abstract class BaseModule(millSourcePath0: Path,
+abstract class BaseModule(millSourcePath0: os.Path,
                           external0: Boolean = false,
                           foreign0 : Boolean = false)
                          (implicit millModuleEnclosing0: sourcecode.Enclosing,
diff --git a/main/core/src/mill/define/Ctx.scala b/main/core/src/mill/define/Ctx.scala
index ba4fae9e..c21e53b4 100644
--- a/main/core/src/mill/define/Ctx.scala
+++ b/main/core/src/mill/define/Ctx.scala
@@ -1,8 +1,6 @@
 package mill.define
 
 
-import ammonite.ops.Path
-
 import scala.annotation.implicitNotFound
 
 sealed trait Segment{
@@ -18,7 +16,7 @@ object Segment{
   case class Cross(value: Seq[Any]) extends Segment
 }
 
-case class BasePath(value: Path)
+case class BasePath(value: os.Path)
 
 
 /**
@@ -64,7 +62,7 @@ object Segments {
 case class Ctx(enclosing: String,
                lineNum: Int,
                segment: Segment,
-               millSourcePath: Path,
+               millSourcePath: os.Path,
                segments: Segments,
                overrides: Int,
                external: Boolean,
diff --git a/main/core/src/mill/define/Module.scala b/main/core/src/mill/define/Module.scala
index f72ec8ca..a8fc5be7 100644
--- a/main/core/src/mill/define/Module.scala
+++ b/main/core/src/mill/define/Module.scala
@@ -2,7 +2,6 @@ package mill.define
 
 import java.lang.reflect.Modifier
 
-import ammonite.ops.Path
 import mill.util.ParseArgs
 
 import scala.language.experimental.macros
@@ -27,7 +26,7 @@ class Module(implicit outerCtx0: mill.define.Ctx)
 
   lazy val millModuleDirectChildren = millInternal.reflectNestedObjects[Module].toSeq
   def millOuterCtx = outerCtx0
-  def millSourcePath: Path = millOuterCtx.millSourcePath / millOuterCtx.segment.pathSegments
+  def millSourcePath: os.Path = millOuterCtx.millSourcePath / millOuterCtx.segment.pathSegments
   implicit def millModuleExternal: Ctx.External = Ctx.External(millOuterCtx.external)
   implicit def millModuleShared: Ctx.Foreign = Ctx.Foreign(millOuterCtx.foreign)
   implicit def millModuleBasePath: BasePath = BasePath(millSourcePath)
diff --git a/main/core/src/mill/define/Task.scala b/main/core/src/mill/define/Task.scala
index 64e868f8..07576724 100644
--- a/main/core/src/mill/define/Task.scala
+++ b/main/core/src/mill/define/Task.scala
@@ -109,11 +109,11 @@ object Target extends TargetGenerated with Applicative.Applyer[Task, Task, Resul
     )
   }
 
-  def sources(values: Result[ammonite.ops.Path]*)
+  def sources(values: Result[os.Path]*)
              (implicit ctx: mill.define.Ctx): Sources = macro sourcesImpl1
 
   def sourcesImpl1(c: Context)
-                  (values: c.Expr[Result[ammonite.ops.Path]]*)
+                  (values: c.Expr[Result[os.Path]]*)
                   (ctx: c.Expr[mill.define.Ctx]): c.Expr[Sources] = {
     import c.universe._
     val wrapped =
diff --git a/main/core/src/mill/eval/Evaluator.scala b/main/core/src/mill/eval/Evaluator.scala
index 2ffc469b..7cf55fdb 100644
--- a/main/core/src/mill/eval/Evaluator.scala
+++ b/main/core/src/mill/eval/Evaluator.scala
@@ -5,7 +5,6 @@ import java.net.URLClassLoader
 import scala.collection.JavaConverters._
 
 import mill.util.Router.EntryPoint
-import ammonite.ops._
 import ammonite.runtime.SpecialClassLoader
 import mill.define.{Ctx => _, _}
 import mill.eval.Result.OuterStack
@@ -29,17 +28,17 @@ case class Labelled[T](task: NamedTask[T],
   }
 }
 
-case class Evaluator(home: Path,
-                     outPath: Path,
-                     externalOutPath: Path,
+case class Evaluator(home: os.Path,
+                     outPath: os.Path,
+                     externalOutPath: os.Path,
                      rootModule: mill.define.BaseModule,
                      log: Logger,
-                     classLoaderSig: Seq[(Either[String, Path], Long)] = Evaluator.classLoaderSig,
+                     classLoaderSig: Seq[(Either[String, os.Path], Long)] = Evaluator.classLoaderSig,
                      workerCache: mutable.Map[Segments, (Int, Any)] = mutable.Map.empty,
                      env : Map[String, String] = Evaluator.defaultEnv){
   val classLoaderSignHash = classLoaderSig.hashCode()
   def evaluate(goals: Agg[Task[_]]): Evaluator.Results = {
-    mkdir(outPath)
+    os.makeDir.all(outPath)
 
    val (sortedGroups, transitive) = Evaluator.plan(rootModule, goals)
 
@@ -76,7 +75,7 @@ case class Evaluator(home: Path,
         vs.items.flatMap(results.get).collect{case f: Result.Failing[_] => f.map(_._1)}
       )
     }
-    write.over(
+    os.write.over(
       outPath / "mill-profile.json",
       upickle.default.write(
         timings .map{case (k, v, b) =>
@@ -133,7 +132,7 @@ case class Evaluator(home: Path,
           destSegments(labelledNamedTask)
         )
 
-        if (!exists(paths.out)) mkdir(paths.out)
+        if (!os.exists(paths.out)) os.makeDir.all(paths.out)
         val cached = for{
           cached <-
             try Some(upickle.default.read[Evaluator.Cached](paths.meta.toIO))
@@ -158,14 +157,13 @@ case class Evaluator(home: Path,
             (newResults, Nil, true)
 
           case _ =>
-
             val Seq(first, rest @_*) = labelledNamedTask.segments.value
             val msgParts = Seq(first.asInstanceOf[Segment.Label].value) ++ rest.map{
               case Segment.Label(s) => "." + s
               case Segment.Cross(s) => "[" + s.mkString(",") + "]"
             }
 
-            if (labelledNamedTask.task.flushDest) rm(paths.dest)
+            if (labelledNamedTask.task.flushDest) os.remove.all(paths.dest)
 
             val (newResults, newEvaluated) = evaluateGroup(
               group,
@@ -188,7 +186,7 @@ case class Evaluator(home: Path,
                 // a following run won't look at the cached metadata file and
                 // assume it's associated with the possibly-borked state of the
                 // destPath after an evaluation failure.
-                rm(paths.meta)
+                os.remove.all(paths.meta)
             }
 
             (newResults, newEvaluated, false)
@@ -218,7 +216,7 @@ case class Evaluator(home: Path,
 
   def handleTaskResult(v: Any,
                        hashCode: Int,
-                       metaPath: Path,
+                       metaPath: os.Path,
                        inputsHash: Int,
                        labelledNamedTask: Labelled[_]) = {
     labelledNamedTask.task.asWorker match{
@@ -230,7 +228,7 @@ case class Evaluator(home: Path,
           .map(w => upickle.default.writeJs(v)(w) -> v)
 
         for((json, v) <- terminalResult){
-          write.over(
+          os.write.over(
             metaPath,
             upickle.default.write(
               Evaluator.Cached(json, hashCode, inputsHash),
@@ -270,7 +268,13 @@ case class Evaluator(home: Path,
     for (task <- nonEvaluatedTargets) {
       newEvaluated.append(task)
       val targetInputValues = task.inputs
-        .map(x => newResults.getOrElse(x, results(x)))
+        .map{x =>
+          val res = newResults.getOrElse(x, results(x))
+          if (!res.isInstanceOf[Result.Success[_]]){
+            println("FAILURE " + x)
+          }
+          res
+        }
         .collect{ case Result.Success((v, hashCode)) => v }
 
       val res =
@@ -291,7 +295,7 @@ case class Evaluator(home: Path,
 
                 paths match{
                   case Some(dest) =>
-                    if (usedDest.isEmpty) mkdir(dest.dest)
+                    if (usedDest.isEmpty) os.makeDir.all(dest.dest)
                     usedDest = Some((task, new Exception().getStackTrace))
                     dest.dest
                   case None =>
@@ -340,7 +344,7 @@ case class Evaluator(home: Path,
     (newResults, newEvaluated)
   }
 
-  def resolveLogger(logPath: Option[Path]): Logger = logPath match{
+  def resolveLogger(logPath: Option[os.Path]): Logger = logPath match{
     case None => log
     case Some(path) => MultiLogger(log.colored, log, FileLogger(log.colored, path, debugEnabled = true))
   }
@@ -355,9 +359,9 @@ object Evaluator{
     implicit val rw: upickle.default.ReadWriter[Cached] = upickle.default.macroRW
   }
   case class State(rootModule: mill.define.BaseModule,
-                   classLoaderSig: Seq[(Either[String, Path], Long)],
+                   classLoaderSig: Seq[(Either[String, os.Path], Long)],
                    workerCache: mutable.Map[Segments, (Int, Any)],
-                   watched: Seq[(Path, Long)])
+                   watched: Seq[(os.Path, Long)])
   // This needs to be a ThreadLocal because we need to pass it into the body of
   // the TargetScopt#read call, which does not accept additional parameters.
   // Until we migrate our CLI parsing off of Scopt (so we can pass the BaseModule
@@ -366,15 +370,15 @@ object Evaluator{
 
   val defaultEnv: Map[String, String] = System.getenv().asScala.toMap
 
-  case class Paths(out: Path,
-                   dest: Path,
-                   meta: Path,
-                   log: Path)
+  case class Paths(out: os.Path,
+                   dest: os.Path,
+                   meta: os.Path,
+                   log: os.Path)
   def makeSegmentStrings(segments: Segments) = segments.value.flatMap{
     case Segment.Label(s) => Seq(s)
     case Segment.Cross(values) => values.map(_.toString)
   }
-  def resolveDestPaths(workspacePath: Path, segments: Segments): Paths = {
+  def resolveDestPaths(workspacePath: os.Path, segments: Segments): Paths = {
     val segmentStrings = makeSegmentStrings(segments)
     val targetPath = workspacePath / segmentStrings
     Paths(targetPath, targetPath / 'dest, targetPath / "meta.json", targetPath / 'log)
diff --git a/main/core/src/mill/eval/PathRef.scala b/main/core/src/mill/eval/PathRef.scala
index 4983f040..92ef8d24 100644
--- a/main/core/src/mill/eval/PathRef.scala
+++ b/main/core/src/mill/eval/PathRef.scala
@@ -7,54 +7,41 @@ import java.nio.{file => jnio}
 import java.security.{DigestOutputStream, MessageDigest}
 
 import upickle.default.{ReadWriter => RW}
-import ammonite.ops.Path
 import mill.util.{DummyOutputStream, IO, JsonFormatters}
 
 
 /**
-  * A wrapper around `ammonite.ops.Path` that calculates it's hashcode based
+  * A wrapper around `os.Path` that calculates it's hashcode based
   * on the contents of the filesystem underneath it. Used to ensure filesystem
   * changes can bust caches which are keyed off hashcodes.
   */
-case class PathRef(path: ammonite.ops.Path, quick: Boolean, sig: Int){
+case class PathRef(path: os.Path, quick: Boolean, sig: Int){
   override def hashCode() = sig
 }
 
 object PathRef{
-  def apply(path: ammonite.ops.Path, quick: Boolean = false) = {
+  def apply(path: os.Path, quick: Boolean = false) = {
     val sig = {
       val digest = MessageDigest.getInstance("MD5")
       val digestOut = new DigestOutputStream(DummyOutputStream, digest)
-      jnio.Files.walkFileTree(
-        path.toNIO,
-        java.util.EnumSet.of(jnio.FileVisitOption.FOLLOW_LINKS),
-        Integer.MAX_VALUE,
-        new FileVisitor[jnio.Path] {
-          def preVisitDirectory(dir: jnio.Path, attrs: BasicFileAttributes) = {
-            digest.update(dir.toAbsolutePath.toString.getBytes)
-            FileVisitResult.CONTINUE
-          }
-
-          def visitFile(file: jnio.Path, attrs: BasicFileAttributes) = {
-            digest.update(file.toAbsolutePath.toString.getBytes)
+      if (os.exists(path)){
+        for((path, attrs) <- os.walk.attrs(path, includeTarget = true, followLinks = true)){
+          digest.update(path.toString.getBytes)
+          if (!attrs.isDir) {
             if (quick){
-              val value = (path.mtime.toMillis, path.size).hashCode()
+              val value = (attrs.mtime, attrs.size).hashCode()
               digest.update((value >>> 24).toByte)
               digest.update((value >>> 16).toByte)
               digest.update((value >>> 8).toByte)
               digest.update(value.toByte)
-            } else if (jnio.Files.isReadable(file)) {
-              val is = jnio.Files.newInputStream(file)
+            } else if (jnio.Files.isReadable(path.toNIO)) {
+              val is = os.read.inputStream(path)
               IO.stream(is, digestOut)
               is.close()
             }
-            FileVisitResult.CONTINUE
           }
-
-          def visitFileFailed(file: jnio.Path, exc: IOException) = FileVisitResult.CONTINUE
-          def postVisitDirectory(dir: jnio.Path, exc: IOException) = FileVisitResult.CONTINUE
         }
-      )
+      }
 
       java.util.Arrays.hashCode(digest.digest())
 
@@ -71,7 +58,7 @@ object PathRef{
     s => {
       val Array(prefix, hex, path) = s.split(":", 3)
       PathRef(
-        Path(path),
+        os.Path(path),
         prefix match{ case "qref" => true case "ref" => false},
         // Parsing to a long and casting to an int is the only way to make
         // round-trip handling of negative numbers work =(
diff --git a/main/core/src/mill/util/ClassLoader.scala b/main/core/src/mill/util/ClassLoader.scala
index ebe8e50b..07ab1ca9 100644
--- a/main/core/src/mill/util/ClassLoader.scala
+++ b/main/core/src/mill/util/ClassLoader.scala
@@ -2,7 +2,7 @@ package mill.util
 
 import java.net.{URL, URLClassLoader}
 
-import ammonite.ops._
+
 import io.github.retronym.java9rtexport.Export
 
 import scala.util.Try
diff --git a/main/core/src/mill/util/Ctx.scala b/main/core/src/mill/util/Ctx.scala
index 6c8b2afb..bbc243b7 100644
--- a/main/core/src/mill/util/Ctx.scala
+++ b/main/core/src/mill/util/Ctx.scala
@@ -1,6 +1,5 @@
 package mill.util
 
-import ammonite.ops.Path
 import mill.define.Applicative.ImplicitStub
 
 import scala.annotation.compileTimeOnly
@@ -12,16 +11,16 @@ object Ctx{
   implicit def taskCtx: Ctx = ???
 
   object Dest {
-    implicit def pathToCtx(path: Path): Dest = new Dest { def dest = path }
+    implicit def pathToCtx(path: os.Path): Dest = new Dest { def dest = path }
   }
   trait Dest{
-    def dest: Path
+    def dest: os.Path
   }
   trait Log{
     def log: Logger
   }
   trait Home{
-    def home: Path
+    def home: os.Path
   }
   trait Env{
     def env: Map[String, String]
@@ -37,9 +36,9 @@ object Ctx{
 
 }
 class Ctx(val args: IndexedSeq[_],
-          dest0: () => Path,
+          dest0: () => os.Path,
           val log: Logger,
-          val home: Path,
+          val home: os.Path,
           val env : Map[String, String])
   extends Ctx.Dest
   with Ctx.Log
diff --git a/main/core/src/mill/util/JsonFormatters.scala b/main/core/src/mill/util/JsonFormatters.scala
index 2728d94d..e2c3073f 100644
--- a/main/core/src/mill/util/JsonFormatters.scala
+++ b/main/core/src/mill/util/JsonFormatters.scala
@@ -1,15 +1,14 @@
 package mill.util
 
-import ammonite.ops.{Bytes, Path}
 import upickle.Js
 import upickle.default.{ReadWriter => RW}
 import scala.util.matching.Regex
 object JsonFormatters extends JsonFormatters
 trait JsonFormatters {
-  implicit val pathReadWrite: RW[ammonite.ops.Path] = upickle.default.readwriter[String]
-    .bimap[ammonite.ops.Path](
+  implicit val pathReadWrite: RW[os.Path] = upickle.default.readwriter[String]
+    .bimap[os.Path](
       _.toString,
-      Path(_)
+      os.Path(_)
     )
 
   implicit val regexReadWrite: RW[Regex] = upickle.default.readwriter[String]
@@ -18,14 +17,14 @@ trait JsonFormatters {
       _.r
     )
 
-  implicit val bytesReadWrite: RW[Bytes] = upickle.default.readwriter[String]
+  implicit val bytesReadWrite: RW[os.Bytes] = upickle.default.readwriter[String]
     .bimap(
-      o => javax.xml.bind.DatatypeConverter.printBase64Binary(o.array),
-      str => new Bytes(javax.xml.bind.DatatypeConverter.parseBase64Binary(str))
+      o => java.util.Base64.getEncoder.encodeToString(o.array),
+      str => new os.Bytes(java.util.Base64.getDecoder.decode(str))
     )
 
 
-  implicit lazy val crFormat: RW[ammonite.ops.CommandResult] = upickle.default.macroRW
+  implicit lazy val crFormat: RW[os.CommandResult] = upickle.default.macroRW
 
   implicit lazy val modFormat: RW[coursier.Module] = upickle.default.macroRW
   implicit lazy val depFormat: RW[coursier.Dependency]= upickle.default.macroRW
diff --git a/main/core/src/mill/util/Logger.scala b/main/core/src/mill/util/Logger.scala
index 1db66039..4857953d 100644
--- a/main/core/src/mill/util/Logger.scala
+++ b/main/core/src/mill/util/Logger.scala
@@ -2,7 +2,6 @@ package mill.util
 
 import java.io._
 
-import ammonite.ops.{Path, rm}
 import ammonite.util.Colors
 
 /**
@@ -142,17 +141,17 @@ case class PrintLogger(
   }
 }
 
-case class FileLogger(colored: Boolean, file: Path, debugEnabled: Boolean) extends Logger {
+case class FileLogger(colored: Boolean, file: os.Path, debugEnabled: Boolean) extends Logger {
   private[this] var outputStreamUsed: Boolean = false
 
   lazy val outputStream = {
-    if (!outputStreamUsed) rm(file)
+    if (!outputStreamUsed) os.remove.all(file)
     outputStreamUsed = true
     new PrintStream(new FileOutputStream(file.toIO.getAbsolutePath))
   }
 
   lazy val errorStream = {
-    if (!outputStreamUsed) rm(file)
+    if (!outputStreamUsed) os.remove.all(file)
     outputStreamUsed = true
     new PrintStream(new FileOutputStream(file.toIO.getAbsolutePath))
   }
diff --git a/main/core/src/mill/util/Scripts.scala b/main/core/src/mill/util/Scripts.scala
index 1815b6de..65eb6b2b 100644
--- a/main/core/src/mill/util/Scripts.scala
+++ b/main/core/src/mill/util/Scripts.scala
@@ -2,7 +2,7 @@ package mill.util
 
 import java.nio.file.NoSuchFileException
 
-import ammonite.ops._
+
 import ammonite.runtime.Evaluator.AmmoniteExit
 import ammonite.util.Name.backtickWrap
 import ammonite.util.Util.CodeSource
@@ -31,15 +31,15 @@ object Scripts {
     scriptArgs
   }
 
-  def runScript(wd: Path,
-                path: Path,
+  def runScript(wd: os.Path,
+                path: os.Path,
                 interp: ammonite.interp.Interpreter,
                 scriptArgs: Seq[(String, Option[String])] = Nil) = {
     interp.watch(path)
     val (pkg, wrapper) = Util.pathToPackageWrapper(Seq(), path relativeTo wd)
 
     for{
-      scriptTxt <- try Res.Success(Util.normalizeNewlines(read(path))) catch{
+      scriptTxt <- try Res.Success(Util.normalizeNewlines(os.read(path))) catch{
         case e: NoSuchFileException => Res.Failure("Script file not found: " + path)
       }
 
@@ -169,7 +169,7 @@ object Scripts {
       for((lhs, rhs) <- args)
         yield {
           val lhsPadded = lhs.padTo(leftColWidth, ' ')
-          val rhsPadded = rhs.lines.mkString(Util.newLine)
+          val rhsPadded = rhs.linesIterator.mkString(Util.newLine)
           s"$leftIndentStr  $lhsPadded  $rhsPadded"
         }
     val mainDocSuffix = main.doc match{
@@ -273,7 +273,7 @@ object Scripts {
   }
 
   def softWrap(s: String, leftOffset: Int, maxWidth: Int) = {
-    val oneLine = s.lines.mkString(" ").split(' ')
+    val oneLine = s.linesIterator.mkString(" ").split(' ')
 
     lazy val indent = " " * leftOffset
 
@@ -325,6 +325,6 @@ object Scripts {
   /**
     * Additional [[scopt.Read]] instance to teach it how to read Ammonite paths
     */
-  implicit def pathScoptRead: scopt.Read[Path] = scopt.Read.stringRead.map(Path(_, pwd))
+  implicit def pathScoptRead: scopt.Read[os.Path] = scopt.Read.stringRead.map(os.Path(_, os.pwd))
 
 }
diff --git a/main/graphviz/src/mill/main/graphviz/GraphvizTools.scala b/main/graphviz/src/mill/main/graphviz/GraphvizTools.scala
index 4e8c59ce..9812c81f 100644
--- a/main/graphviz/src/mill/main/graphviz/GraphvizTools.scala
+++ b/main/graphviz/src/mill/main/graphviz/GraphvizTools.scala
@@ -1,10 +1,9 @@
 package mill.main.graphviz
-import ammonite.ops.Path
 import guru.nidi.graphviz.attribute.Style
 import mill.define.{Graph, NamedTask}
 import org.jgrapht.graph.{DefaultEdge, SimpleDirectedGraph}
 object GraphvizTools{
-  def apply(targets: Seq[NamedTask[Any]], rs: Seq[NamedTask[Any]], dest: Path) = {
+  def apply(targets: Seq[NamedTask[Any]], rs: Seq[NamedTask[Any]], dest: os.Path) = {
     val transitive = Graph.transitiveTargets(rs.distinct)
     val topoSorted = Graph.topoSorted(transitive)
     val goalSet = rs.toSet
diff --git a/main/src/mill/MillMain.scala b/main/src/mill/MillMain.scala
index 1598d5f3..d36b6f42 100644
--- a/main/src/mill/MillMain.scala
+++ b/main/src/mill/MillMain.scala
@@ -4,7 +4,6 @@ import java.io.{InputStream, PrintStream}
 
 import scala.collection.JavaConverters._
 import ammonite.main.Cli._
-import ammonite.ops._
 import io.github.retronym.java9rtexport.Export
 import mill.eval.Evaluator
 import mill.util.DummyInputStream
@@ -110,7 +109,7 @@ object MillMain {
               predefCode =
                 s"""import $$file.build, build._
                   |implicit val replApplyHandler = mill.main.ReplApplyHandler(
-                  |  ammonite.ops.Path(${pprint.apply(cliConfig.home.toIO.getCanonicalPath.replaceAllLiterally("$", "$$")).plainText}),
+                  |  os.Path(${pprint.apply(cliConfig.home.toIO.getCanonicalPath.replaceAllLiterally("$", "$$")).plainText}),
                   |  $disableTicker,
                   |  interp.colors(),
                   |  repl.pprinter(),
@@ -137,7 +136,7 @@ object MillMain {
 
           if (mill.main.client.Util.isJava9OrAbove) {
             val rt = cliConfig.home / Export.rtJarName
-            if (!exists(rt)) {
+            if (!os.exists(rt)) {
               runner.printInfo(s"Preparing Java ${System.getProperty("java.version")} runtime; this may take a minute or two ...")
               Export.rtTo(rt.toIO, false)
             }
@@ -147,7 +146,7 @@ object MillMain {
             runner.printInfo("Loading...")
             (runner.watchLoop(isRepl = true, printing = false, _.run()), runner.stateCache)
           } else {
-            (runner.runScript(pwd / "build.sc", leftoverArgs), runner.stateCache)
+            (runner.runScript(os.pwd / "build.sc", leftoverArgs), runner.stateCache)
           }
       }
 
diff --git a/main/src/mill/main/MainModule.scala b/main/src/mill/main/MainModule.scala
index 929ad3dc..a740a2e6 100644
--- a/main/src/mill/main/MainModule.scala
+++ b/main/src/mill/main/MainModule.scala
@@ -2,7 +2,6 @@ package mill.main
 
 import java.util.concurrent.LinkedBlockingQueue
 
-import ammonite.ops.Path
 import mill.T
 import mill.define.{NamedTask, Task}
 import mill.eval.{Evaluator, PathRef, Result}
@@ -200,7 +199,7 @@ trait MainModule extends mill.Module{
 
     val KeepPattern = "(mill-.+)".r.anchored
 
-    def keepPath(path: Path) = path.segments.lastOption match {
+    def keepPath(path: os.Path) = path.segments.toSeq.lastOption match {
       case Some(KeepPattern(_)) => true
       case _ => false
     }
@@ -220,7 +219,7 @@ trait MainModule extends mill.Module{
       case Left(err) =>
         Result.Failure(err)
       case Right(paths) =>
-        paths.foreach(ammonite.ops.rm)
+        paths.foreach(os.remove.all)
         Result.Success(())
     }
   }
@@ -245,7 +244,7 @@ trait MainModule extends mill.Module{
     }
   }
 
-  private type VizWorker = (LinkedBlockingQueue[(scala.Seq[_], scala.Seq[_], Path)],
+  private type VizWorker = (LinkedBlockingQueue[(scala.Seq[_], scala.Seq[_], os.Path)],
     LinkedBlockingQueue[Result[scala.Seq[PathRef]]])
 
   private def visualize0(evaluator: Evaluator, targets: Seq[String], ctx: Ctx, vizWorker: VizWorker,
diff --git a/main/src/mill/main/MainRunner.scala b/main/src/mill/main/MainRunner.scala
index 4f31a724..e50ed370 100644
--- a/main/src/mill/main/MainRunner.scala
+++ b/main/src/mill/main/MainRunner.scala
@@ -3,7 +3,6 @@ import java.io.{InputStream, PrintStream}
 
 import ammonite.Main
 import ammonite.interp.{Interpreter, Preprocessor}
-import ammonite.ops.Path
 import ammonite.util.Util.CodeSource
 import ammonite.util._
 import mill.eval.{Evaluator, PathRef}
@@ -33,7 +32,7 @@ class MainRunner(val config: ammonite.main.Cli.Config,
 
   var stateCache  = stateCache0
 
-  override def watchAndWait(watched: Seq[(Path, Long)]) = {
+  override def watchAndWait(watched: Seq[(os.Path, Long)]) = {
     printInfo(s"Watching for changes to ${watched.length} files... (Ctrl-C to exit)")
     def statAll() = watched.forall{ case (file, lastMTime) =>
       Interpreter.pathSignature(file) == lastMTime
@@ -50,7 +49,7 @@ class MainRunner(val config: ammonite.main.Cli.Config,
     */
   @tailrec final def watchLoop2[T](isRepl: Boolean,
                                    printing: Boolean,
-                                   run: Main => (Res[T], () => Seq[(Path, Long)])): Boolean = {
+                                   run: Main => (Res[T], () => Seq[(os.Path, Long)])): Boolean = {
     val (result, watched) = run(initMain(isRepl))
 
     val success = handleWatchRes(result, printing)
@@ -62,7 +61,7 @@ class MainRunner(val config: ammonite.main.Cli.Config,
   }
 
 
-  override def runScript(scriptPath: Path, scriptArgs: List[String]) =
+  override def runScript(scriptPath: os.Path, scriptArgs: List[String]) =
     watchLoop2(
       isRepl = false,
       printing = true,
@@ -146,7 +145,7 @@ class MainRunner(val config: ammonite.main.Cli.Config,
         |$imports
         |import mill._
         |object $wrapName
-        |extends mill.define.BaseModule(ammonite.ops.Path($literalPath), foreign0 = $external)(
+        |extends mill.define.BaseModule(os.Path($literalPath), foreign0 = $external)(
         |  implicitly, implicitly, implicitly, implicitly, mill.define.Caller(())
         |)
         |with $wrapName{
diff --git a/main/src/mill/main/ReplApplyHandler.scala b/main/src/mill/main/ReplApplyHandler.scala
index af69c761..a8e467d4 100644
--- a/main/src/mill/main/ReplApplyHandler.scala
+++ b/main/src/mill/main/ReplApplyHandler.scala
@@ -1,7 +1,6 @@
 package mill.main
 
 
-import ammonite.ops.Path
 import mill.define.Applicative.ApplyHandler
 import mill.define.Segment.Label
 import mill.define._
@@ -11,7 +10,7 @@ import mill.util.Strict.Agg
 
 import scala.collection.mutable
 object ReplApplyHandler{
-  def apply[T](home: Path,
+  def apply[T](home: os.Path,
                disableTicker: Boolean,
                colors: ammonite.util.Colors,
                pprinter0: pprint.PPrinter,
diff --git a/main/src/mill/main/RunScript.scala b/main/src/mill/main/RunScript.scala
index 1c8503fe..820b1341 100644
--- a/main/src/mill/main/RunScript.scala
+++ b/main/src/mill/main/RunScript.scala
@@ -3,7 +3,6 @@ package mill.main
 import java.nio.file.NoSuchFileException
 
 import ammonite.interp.Interpreter
-import ammonite.ops.{Path, read}
 import ammonite.runtime.SpecialClassLoader
 import ammonite.util.Util.CodeSource
 import ammonite.util.{Name, Res, Util}
@@ -23,15 +22,15 @@ import scala.reflect.ClassTag
   * subsystem
   */
 object RunScript{
-  def runScript(home: Path,
-                wd: Path,
-                path: Path,
-                instantiateInterpreter: => Either[(Res.Failing, Seq[(Path, Long)]), ammonite.interp.Interpreter],
+  def runScript(home: os.Path,
+                wd: os.Path,
+                path: os.Path,
+                instantiateInterpreter: => Either[(Res.Failing, Seq[(os.Path, Long)]), ammonite.interp.Interpreter],
                 scriptArgs: Seq[String],
                 stateCache: Option[Evaluator.State],
                 log: Logger,
                 env : Map[String, String])
-  : (Res[(Evaluator, Seq[PathRef], Either[String, Seq[Js.Value]])], Seq[(Path, Long)]) = {
+  : (Res[(Evaluator, Seq[PathRef], Either[String, Seq[Js.Value]])], Seq[(os.Path, Long)]) = {
 
     val (evalState, interpWatched) = stateCache match{
       case Some(s) if watchedSigUnchanged(s.watched) => Res.Success(s) -> s.watched
@@ -66,12 +65,12 @@ object RunScript{
     (evaluated, interpWatched)
   }
 
-  def watchedSigUnchanged(sig: Seq[(Path, Long)]) = {
+  def watchedSigUnchanged(sig: Seq[(os.Path, Long)]) = {
     sig.forall{case (p, l) => Interpreter.pathSignature(p) == l}
   }
 
-  def evaluateRootModule(wd: Path,
-                         path: Path,
+  def evaluateRootModule(wd: os.Path,
+                         path: os.Path,
                          interp: ammonite.interp.Interpreter,
                          log: Logger
                         ): Res[mill.define.BaseModule] = {
@@ -80,7 +79,7 @@ object RunScript{
 
     for {
       scriptTxt <-
-        try Res.Success(Util.normalizeNewlines(read(path)))
+        try Res.Success(Util.normalizeNewlines(os.read(path)))
         catch { case _: NoSuchFileException =>
           log.info("No build file found, you should create build.sc to do something useful")
           Res.Success("")
diff --git a/main/src/mill/main/VisualizeModule.scala b/main/src/mill/main/VisualizeModule.scala
index ea4d46c6..71b9fc22 100644
--- a/main/src/mill/main/VisualizeModule.scala
+++ b/main/src/mill/main/VisualizeModule.scala
@@ -2,7 +2,6 @@ package mill.main
 
 import java.util.concurrent.LinkedBlockingQueue
 
-import ammonite.ops.Path
 import coursier.Cache
 import coursier.core.Repository
 import coursier.maven.MavenRepository
@@ -35,7 +34,7 @@ trait VisualizeModule extends mill.define.TaskModule{
     * can communicate via in/out queues.
     */
   def worker = T.worker{
-    val in = new LinkedBlockingQueue[(Seq[_], Seq[_], Path)]()
+    val in = new LinkedBlockingQueue[(Seq[_], Seq[_], os.Path)]()
     val out = new LinkedBlockingQueue[Result[Seq[PathRef]]]()
 
     val cl = mill.util.ClassLoader.create(
@@ -47,7 +46,7 @@ trait VisualizeModule extends mill.define.TaskModule{
         val res = Result.create{
           val (targets, tasks, dest) = in.take()
           cl.loadClass("mill.main.graphviz.GraphvizTools")
-            .getMethod("apply", classOf[Seq[_]], classOf[Seq[_]], classOf[Path])
+            .getMethod("apply", classOf[Seq[_]], classOf[Seq[_]], classOf[os.Path])
             .invoke(null, targets, tasks, dest)
             .asInstanceOf[Seq[PathRef]]
         }
diff --git a/main/src/mill/modules/Assembly.scala b/main/src/mill/modules/Assembly.scala
index b7b91248..141bc226 100644
--- a/main/src/mill/modules/Assembly.scala
+++ b/main/src/mill/modules/Assembly.scala
@@ -4,7 +4,6 @@ import java.io.InputStream
 import java.util.jar.JarFile
 import java.util.regex.Pattern
 
-import ammonite.ops._
 import geny.Generator
 import mill.Agg
 
@@ -37,7 +36,7 @@ object Assembly {
     case class ExcludePattern(pattern: Pattern) extends Rule
   }
 
-  def groupAssemblyEntries(inputPaths: Agg[Path], assemblyRules: Seq[Assembly.Rule]): Map[String, GroupedEntry] = {
+  def groupAssemblyEntries(inputPaths: Agg[os.Path], assemblyRules: Seq[Assembly.Rule]): Map[String, GroupedEntry] = {
     val rulesMap = assemblyRules.collect {
       case r@Rule.Append(path) => path -> r
       case r@Rule.Exclude(path) => path -> r
@@ -76,12 +75,12 @@ object Assembly {
     }
   }
 
-  private def classpathIterator(inputPaths: Agg[Path]): Generator[AssemblyEntry] = {
+  private def classpathIterator(inputPaths: Agg[os.Path]): Generator[AssemblyEntry] = {
     Generator.from(inputPaths)
-      .filter(exists)
+      .filter(os.exists)
       .flatMap {
         p =>
-          if (p.isFile) {
+          if (os.isFile(p)) {
             val jf = new JarFile(p.toIO)
             Generator.from(
               for(entry <- jf.entries().asScala if !entry.isDirectory)
@@ -89,8 +88,8 @@ object Assembly {
             )
           }
           else {
-            ls.rec.iter(p)
-              .filter(_.isFile)
+            os.walk.stream(p)
+              .filter(os.isFile)
               .map(sub => PathEntry(sub.relativeTo(p).toString, sub))
           }
       }
@@ -118,8 +117,8 @@ private[this] sealed trait AssemblyEntry {
   def inputStream: InputStream
 }
 
-private[this] case class PathEntry(mapping: String, path: Path) extends AssemblyEntry {
-  def inputStream: InputStream = read.getInputStream(path)
+private[this] case class PathEntry(mapping: String, path: os.Path) extends AssemblyEntry {
+  def inputStream: InputStream = os.read.inputStream(path)
 }
 
 private[this] case class JarFileEntry(mapping: String, getIs: () => InputStream) extends AssemblyEntry {
diff --git a/main/src/mill/modules/Jvm.scala b/main/src/mill/modules/Jvm.scala
index 4c26b297..b4a55de3 100644
--- a/main/src/mill/modules/Jvm.scala
+++ b/main/src/mill/modules/Jvm.scala
@@ -8,7 +8,6 @@ import java.nio.file.attribute.PosixFilePermission
 import java.util.Collections
 import java.util.jar.{JarEntry, JarFile, JarOutputStream}
 
-import ammonite.ops._
 import coursier.{Cache, Dependency, Fetch, Repository, Resolution}
 import coursier.util.{Gather, Task}
 import geny.Generator
@@ -23,11 +22,11 @@ import scala.collection.JavaConverters._
 object Jvm {
 
   def interactiveSubprocess(mainClass: String,
-                            classPath: Agg[Path],
+                            classPath: Agg[os.Path],
                             jvmArgs: Seq[String] = Seq.empty,
                             envArgs: Map[String, String] = Map.empty,
                             mainArgs: Seq[String] = Seq.empty,
-                            workingDir: Path = null,
+                            workingDir: os.Path = null,
                             background: Boolean = false): Unit = {
     val args =
       Vector("java") ++
@@ -41,16 +40,16 @@ object Jvm {
 
   def baseInteractiveSubprocess(commandArgs: Seq[String],
                                 envArgs: Map[String, String],
-                                workingDir: Path) = {
+                                workingDir: os.Path) = {
     val process = baseInteractiveSubprocess0(commandArgs, envArgs, workingDir)
 
     val exitCode = process.waitFor()
     if (exitCode == 0) ()
-    else throw InteractiveShelloutException()
+    else throw new Exception("Interactive Subprocess Failed")
   }
   def baseInteractiveSubprocess0(commandArgs: Seq[String],
                                  envArgs: Map[String, String],
-                                 workingDir: Path) = {
+                                 workingDir: os.Path) = {
     val builder = new java.lang.ProcessBuilder()
 
     for ((k, v) <- envArgs){
@@ -86,7 +85,7 @@ object Jvm {
 
 
   def runLocal(mainClass: String,
-               classPath: Agg[Path],
+               classPath: Agg[os.Path],
                mainArgs: Seq[String] = Seq.empty)
               (implicit ctx: Ctx): Unit = {
     inprocess(classPath, classLoaderOverrideSbtTesting = false, isolated = true, closeContextClassLoaderWhenDone = true, cl => {
@@ -110,7 +109,7 @@ object Jvm {
 
 
 
-  def inprocess[T](classPath: Agg[Path],
+  def inprocess[T](classPath: Agg[os.Path],
                    classLoaderOverrideSbtTesting: Boolean,
                    isolated: Boolean,
                    closeContextClassLoaderWhenDone: Boolean,
@@ -143,11 +142,11 @@ object Jvm {
   }
 
   def subprocess(mainClass: String,
-                 classPath: Agg[Path],
+                 classPath: Agg[os.Path],
                  jvmArgs: Seq[String] = Seq.empty,
                  envArgs: Map[String, String] = Map.empty,
                  mainArgs: Seq[String] = Seq.empty,
-                 workingDir: Path = null)
+                 workingDir: os.Path = null)
                 (implicit ctx: Ctx) = {
 
     val commandArgs =
@@ -157,7 +156,7 @@ object Jvm {
       mainArgs
 
     val workingDir1 = Option(workingDir).getOrElse(ctx.dest)
-    mkdir(workingDir1)
+    os.makeDir.all(workingDir1)
     val builder =
       new java.lang.ProcessBuilder()
         .directory(workingDir1.toIO)
@@ -170,10 +169,10 @@ object Jvm {
     val stdout = proc.getInputStream
     val stderr = proc.getErrorStream
     val sources = Seq(
-      (stdout, Left(_: Bytes), ctx.log.outputStream),
-      (stderr, Right(_: Bytes),ctx.log.errorStream )
+      (stdout, Left(_: os.Bytes), ctx.log.outputStream),
+      (stderr, Right(_: os.Bytes),ctx.log.errorStream )
     )
-    val chunks = mutable.Buffer.empty[Either[Bytes, Bytes]]
+    val chunks = mutable.Buffer.empty[Either[os.Bytes, os.Bytes]]
     while(
     // Process.isAlive doesn't exist on JDK 7 =/
       util.Try(proc.exitValue).isFailure ||
@@ -186,7 +185,7 @@ object Jvm {
           readSomething = true
           val array = new Array[Byte](subStream.available())
           val actuallyRead = subStream.read(array)
-          chunks.append(wrapper(new ammonite.ops.Bytes(array)))
+          chunks.append(wrapper(new os.Bytes(array)))
           parentStream.write(array, 0, actuallyRead)
         }
       }
@@ -195,8 +194,8 @@ object Jvm {
         Thread.sleep(2)
     }
 
-    if (proc.exitValue() != 0) throw new InteractiveShelloutException()
-    else ammonite.ops.CommandResult(proc.exitValue(), chunks)
+    if (proc.exitValue() != 0) throw new Exception("Subprocess failed")
+    else os.CommandResult(proc.exitValue(), chunks)
   }
 
   private def createManifest(mainClass: Option[String]) = {
@@ -214,42 +213,42 @@ object Jvm {
     * called out.jar in the implicit ctx.dest folder. An optional main class may
     * be provided for the jar. An optional filter function may also be provided to
     * selectively include/exclude specific files.
-    * @param inputPaths - `Agg` of `Path`s containing files to be included in the jar
+    * @param inputPaths - `Agg` of `os.Path`s containing files to be included in the jar
     * @param mainClass - optional main class for the jar
     * @param fileFilter - optional file filter to select files to be included.
-    *                   Given a `Path` (from inputPaths) and a `RelPath` for the individual file,
+    *                   Given a `os.Path` (from inputPaths) and a `os.RelPath` for the individual file,
     *                   return true if the file is to be included in the jar.
     * @param ctx - implicit `Ctx.Dest` used to determine the output directory for the jar.
     * @return - a `PathRef` for the created jar.
     */
-  def createJar(inputPaths: Agg[Path],
+  def createJar(inputPaths: Agg[os.Path],
                 mainClass: Option[String] = None,
-                fileFilter: (Path, RelPath) => Boolean = (p: Path, r: RelPath) => true)
+                fileFilter: (os.Path, os.RelPath) => Boolean = (p: os.Path, r: os.RelPath) => true)
                (implicit ctx: Ctx.Dest): PathRef = {
     val outputPath = ctx.dest / "out.jar"
-    rm(outputPath)
+    os.remove.all(outputPath)
 
-    val seen = mutable.Set.empty[RelPath]
-    seen.add("META-INF" / "MANIFEST.MF")
+    val seen = mutable.Set.empty[os.RelPath]
+    seen.add(os.rel / "META-INF" / "MANIFEST.MF")
     val jar = new JarOutputStream(
       new FileOutputStream(outputPath.toIO),
       createManifest(mainClass)
     )
 
     try{
-      assert(inputPaths.forall(exists(_)))
+      assert(inputPaths.forall(os.exists(_)))
       for{
         p <- inputPaths
         (file, mapping) <-
-          if (p.isFile) Iterator(p -> empty/p.last)
-          else ls.rec(p).filter(_.isFile).map(sub => sub -> sub.relativeTo(p))
+          if (os.isFile(p)) Iterator(p -> os.rel / p.last)
+          else os.walk(p).filter(os.isFile).map(sub => sub -> sub.relativeTo(p)).sorted
         if !seen(mapping) && fileFilter(p, mapping)
       } {
         seen.add(mapping)
         val entry = new JarEntry(mapping.toString)
-        entry.setTime(file.mtime.toMillis)
+        entry.setTime(os.mtime(file))
         jar.putNextEntry(entry)
-        jar.write(read.bytes(file))
+        jar.write(os.read.bytes(file))
         jar.closeEntry()
       }
     } finally {
@@ -259,17 +258,10 @@ object Jvm {
     PathRef(outputPath)
   }
 
-  def newOutputStream(p: java.nio.file.Path, append: Boolean = false) = {
-    val options =
-      if(append) Seq(StandardOpenOption.APPEND)
-      else Seq(StandardOpenOption.TRUNCATE_EXISTING, StandardOpenOption.CREATE)
-    Files.newOutputStream(p, options:_*)
-  }
-
-  def createAssembly(inputPaths: Agg[Path],
+  def createAssembly(inputPaths: Agg[os.Path],
                      mainClass: Option[String] = None,
                      prependShellScript: String = "",
-                     base: Option[Path] = None,
+                     base: Option[os.Path] = None,
                      assemblyRules: Seq[Assembly.Rule] = Assembly.defaultRules)
                     (implicit ctx: Ctx.Dest with Ctx.Log): PathRef = {
 
@@ -279,7 +271,7 @@ object Jvm {
     val hm = new java.util.HashMap[String, String]()
 
     base match{
-      case Some(b) => cp(b, tmp)
+      case Some(b) => os.copy(b, tmp)
       case None => hm.put("create", "true")
     }
 
@@ -288,23 +280,25 @@ object Jvm {
     val manifest = createManifest(mainClass)
     val manifestPath = zipFs.getPath(JarFile.MANIFEST_NAME)
     Files.createDirectories(manifestPath.getParent)
-    val manifestOut = newOutputStream(manifestPath)
+    val manifestOut = Files.newOutputStream(
+      manifestPath,
+      StandardOpenOption.TRUNCATE_EXISTING,
+      StandardOpenOption.CREATE
+    )
     manifest.write(manifestOut)
     manifestOut.close()
 
     Assembly.groupAssemblyEntries(inputPaths, assemblyRules).view
-      .map {
-        case (mapping, aggregate) =>
-          zipFs.getPath(mapping) -> aggregate
-      }
       .foreach {
-        case (path, AppendEntry(entries)) =>
+        case (mapping, AppendEntry(entries)) =>
+          val path = zipFs.getPath(mapping)
           val concatenated = new SequenceInputStream(
             Collections.enumeration(entries.map(_.inputStream).asJava))
-          writeEntry(path, concatenated, append = Files.exists(path))
-        case (path, WriteOnceEntry(entry)) =>
+          writeEntry(os.Path(path), concatenated, append = true)
+        case (mapping, WriteOnceEntry(entry)) =>
+          val path = zipFs.getPath(mapping)
           if (Files.notExists(path)) {
-            writeEntry(path, entry.inputStream, append = false)
+            writeEntry(os.Path(path), entry.inputStream, append = false)
           }
       }
 
@@ -312,33 +306,36 @@ object Jvm {
     val output = ctx.dest / "out.jar"
 
     // Prepend shell script and make it executable
-    if (prependShellScript.isEmpty) mv(tmp, output)
+    if (prependShellScript.isEmpty) os.move(tmp, output)
     else{
       val lineSep = if (!prependShellScript.endsWith("\n")) "\n\r\n" else ""
-      val outputStream = newOutputStream(output.toNIO)
-      IO.stream(new ByteArrayInputStream((prependShellScript + lineSep).getBytes()), outputStream)
-      IO.stream(read.getInputStream(tmp), outputStream)
-      outputStream.close()
+      os.write(
+        output,
+        Seq[os.Source](
+          prependShellScript + lineSep,
+          os.read.inputStream(tmp)
+        )
+      )
 
       if (!scala.util.Properties.isWin) {
-        val perms = Files.getPosixFilePermissions(output.toNIO)
-        perms.add(PosixFilePermission.GROUP_EXECUTE)
-        perms.add(PosixFilePermission.OWNER_EXECUTE)
-        perms.add(PosixFilePermission.OTHERS_EXECUTE)
-        Files.setPosixFilePermissions(output.toNIO, perms)
+        os.perms.set(
+          output,
+          os.perms(output)
+            + PosixFilePermission.GROUP_EXECUTE
+            + PosixFilePermission.OWNER_EXECUTE
+            + PosixFilePermission.OTHERS_EXECUTE
+        )
       }
     }
 
     PathRef(output)
   }
 
-  private def writeEntry(p: java.nio.file.Path, is: InputStream, append: Boolean): Unit = {
-    if (p.getParent != null) Files.createDirectories(p.getParent)
-    val outputStream = newOutputStream(p, append)
-
-    IO.stream(is, outputStream)
+  private def writeEntry(p: os.Path, is: InputStream, append: Boolean): Unit = {
+    if (p.toNIO.getParent != null) Files.createDirectories(p.toNIO.getParent)
+    if (append) os.write(p, is)
+    else os.write.append(p, is)
 
-    outputStream.close()
     is.close()
   }
 
@@ -376,7 +373,7 @@ object Jvm {
     )
   }
   def createLauncher(mainClass: String,
-                     classPath: Agg[Path],
+                     classPath: Agg[os.Path],
                      jvmArgs: Seq[String])
                     (implicit ctx: Ctx.Dest)= {
     val isWin = scala.util.Properties.isWin
@@ -387,7 +384,7 @@ object Jvm {
     val outputPath = ctx.dest / (if (isBatch) "run.bat" else "run")
     val classPathStrs = classPath.map(_.toString)
 
-    write(outputPath, launcherUniversalScript(mainClass, classPathStrs, classPathStrs, jvmArgs))
+    os.write(outputPath, launcherUniversalScript(mainClass, classPathStrs, classPathStrs, jvmArgs))
 
     if (!isWin) {
       val perms = Files.getPosixFilePermissions(outputPath.toNIO)
@@ -454,7 +451,7 @@ object Jvm {
       val (errors, successes) = load(sourceOrJar)
       if(errors.isEmpty){
         mill.Agg.from(
-          successes.map(p => PathRef(Path(p), quick = true)).filter(_.path.ext == "jar")
+          successes.map(p => PathRef(os.Path(p), quick = true)).filter(_.path.ext == "jar")
         )
       }else{
         val errorDetails = errors.map(e => s"${ammonite.util.Util.newLine}  ${e.describe}").mkString
diff --git a/main/src/mill/modules/Util.scala b/main/src/mill/modules/Util.scala
index 38cd056b..2f57595e 100644
--- a/main/src/mill/modules/Util.scala
+++ b/main/src/mill/modules/Util.scala
@@ -1,14 +1,13 @@
 package mill.modules
 
 
-import ammonite.ops.{Path, RelPath, empty, mkdir, read}
 import coursier.Repository
 import mill.eval.PathRef
 import mill.util.{Ctx, IO, Loose}
 
 object Util {
   def cleanupScaladoc(v: String) = {
-    v.lines.map(
+    v.linesIterator.map(
       _.dropWhile(_.isWhitespace)
         .stripPrefix("/**")
         .stripPrefix("*/")
@@ -20,7 +19,7 @@ object Util {
       .dropWhile(_.isEmpty)
       .reverse
   }
-  def download(url: String, dest: RelPath = "download")(implicit ctx: Ctx.Dest) = {
+  def download(url: String, dest: os.RelPath = "download")(implicit ctx: Ctx.Dest) = {
     val out = ctx.dest / dest
 
     val website = new java.net.URI(url).toURL
@@ -38,26 +37,26 @@ object Util {
     }
   }
 
-  def downloadUnpackZip(url: String, dest: RelPath = "unpacked")
+  def downloadUnpackZip(url: String, dest: os.RelPath = "unpacked")
                        (implicit ctx: Ctx.Dest) = {
 
-    val tmpName = if (dest == empty / "tmp.zip") "tmp2.zip" else "tmp.zip"
+    val tmpName = if (dest == os.rel / "tmp.zip") "tmp2.zip" else "tmp.zip"
     val downloaded = download(url, tmpName)
     unpackZip(downloaded.path, dest)
   }
 
-  def unpackZip(src: Path, dest: RelPath = "unpacked")
+  def unpackZip(src: os.Path, dest: os.RelPath = "unpacked")
                (implicit ctx: Ctx.Dest) = {
 
-    val byteStream = read.getInputStream(src)
+    val byteStream = os.read.inputStream(src)
     val zipStream = new java.util.zip.ZipInputStream(byteStream)
     while({
       zipStream.getNextEntry match{
         case null => false
         case entry =>
           if (!entry.isDirectory) {
-            val entryDest = ctx.dest / dest / RelPath(entry.getName)
-            mkdir(entryDest / ammonite.ops.up)
+            val entryDest = ctx.dest / dest / os.RelPath(entry.getName)
+            os.makeDir.all(entryDest / ammonite.ops.up)
             val fileOut = new java.io.FileOutputStream(entryDest.toString)
             IO.stream(zipStream, fileOut)
             fileOut.close()
@@ -72,12 +71,12 @@ object Util {
   def millProjectModule(key: String,
                         artifact: String,
                         repositories: Seq[Repository],
-                        resolveFilter: Path => Boolean = _ => true,
+                        resolveFilter: os.Path => Boolean = _ => true,
                         artifactSuffix: String = "_2.12") = {
     val localPath = sys.props(key)
     if (localPath != null) {
       mill.eval.Result.Success(
-        Loose.Agg.from(localPath.split(',').map(p => PathRef(Path(p), quick = true)))
+        Loose.Agg.from(localPath.split(',').map(p => PathRef(os.Path(p), quick = true)))
       )
     } else {
       mill.modules.Jvm.resolveDependencies(
diff --git a/main/test/resources/examples/foreign/conflict/build.sc b/main/test/resources/examples/foreign/conflict/build.sc
index d6c08b81..bedd7237 100644
--- a/main/test/resources/examples/foreign/conflict/build.sc
+++ b/main/test/resources/examples/foreign/conflict/build.sc
@@ -1,6 +1,5 @@
 import $file.inner.{build => innerBuild}
 import mill._
-import ammonite.ops._
 
 // In this build, we have a local module targeting
 // the 'inner sub-directory, and an imported foreign
@@ -20,5 +19,5 @@ def checkDests : T[Unit] = T {
 }
 
 object inner extends mill.Module {
-  def selfDest = T { T.ctx().dest / up / up }
+  def selfDest = T { T.ctx().dest / os.up / os.up }
 }
diff --git a/main/test/resources/examples/foreign/conflict/inner/build.sc b/main/test/resources/examples/foreign/conflict/inner/build.sc
index 729f4f3d..81e5fc2f 100644
--- a/main/test/resources/examples/foreign/conflict/inner/build.sc
+++ b/main/test/resources/examples/foreign/conflict/inner/build.sc
@@ -1,4 +1,3 @@
 import mill._
-import ammonite.ops._
 
-def selfDest = T { T.ctx().dest / up / up }
+def selfDest = T { T.ctx().dest / os.up / os.up }
diff --git a/main/test/resources/examples/foreign/outer/build.sc b/main/test/resources/examples/foreign/outer/build.sc
index b53cca70..adef19da 100644
--- a/main/test/resources/examples/foreign/outer/build.sc
+++ b/main/test/resources/examples/foreign/outer/build.sc
@@ -1,13 +1,12 @@
 import $file.inner.build
 import mill._
-import ammonite.ops._
 
 trait PathAware extends mill.Module {
   def selfPath = T { millSourcePath }
 }
 
 trait DestAware extends mill.Module {
-  def selfDest = T { T.ctx().dest / up / up }
+  def selfDest = T { T.ctx().dest / os.up / os.up }
 }
 
 object sub extends PathAware with DestAware {
diff --git a/main/test/resources/examples/foreign/outer/inner/build.sc b/main/test/resources/examples/foreign/outer/inner/build.sc
index 2d978292..da103b95 100644
--- a/main/test/resources/examples/foreign/outer/inner/build.sc
+++ b/main/test/resources/examples/foreign/outer/inner/build.sc
@@ -1,12 +1,11 @@
 import mill._
-import ammonite.ops._
 
 trait PathAware extends mill.Module {
   def selfPath = T { millSourcePath }
 }
 
 trait DestAware extends mill.Module {
-  def selfDest = T { T.ctx().dest / up / up }
+  def selfDest = T { T.ctx().dest / os.up / os.up }
 }
 
 object sub extends PathAware with DestAware {
diff --git a/main/test/resources/examples/foreign/project/build.sc b/main/test/resources/examples/foreign/project/build.sc
index 80c2af9b..54686c2d 100644
--- a/main/test/resources/examples/foreign/project/build.sc
+++ b/main/test/resources/examples/foreign/project/build.sc
@@ -1,10 +1,9 @@
 import $file.^.outer.build
 import $file.inner.build
 
-import ammonite.ops._
 import mill._
 
-def assertPaths(p1 : Path, p2 : Path) : Unit = if (p1 != p2) throw new Exception(
+def assertPaths(p1 : os.Path, p2 : os.Path) : Unit = if (p1 != p2) throw new Exception(
   s"Paths were not equal : \n- $p1 \n- $p2"
 )
 
@@ -17,7 +16,7 @@ object sub extends PathAware with DestAware {
 }
 
 def checkProjectPaths = T {
-  val thisPath : Path = millSourcePath
+  val thisPath : os.Path = millSourcePath
   assert(thisPath.last == "project")
   assertPaths(sub.selfPath(), thisPath / 'sub)
   assertPaths(sub.sub.selfPath(), thisPath / 'sub / 'sub)
@@ -25,47 +24,47 @@ def checkProjectPaths = T {
 }
 
 def checkInnerPaths = T {
-  val thisPath : Path = millSourcePath
+  val thisPath : os.Path = millSourcePath
   assertPaths(inner.build.millSourcePath, thisPath / 'inner )
   assertPaths(inner.build.sub.selfPath(), thisPath / 'inner / 'sub)
   assertPaths(inner.build.sub.sub.selfPath(), thisPath / 'inner / 'sub / 'sub)
 }
 
 def checkOuterPaths = T {
-  val thisPath : Path = millSourcePath
-  assertPaths(^.outer.build.millSourcePath, thisPath / up / 'outer )
-  assertPaths(^.outer.build.sub.selfPath(), thisPath / up / 'outer / 'sub)
-  assertPaths(^.outer.build.sub.sub.selfPath(), thisPath / up / 'outer / 'sub / 'sub)
+  val thisPath : os.Path = millSourcePath
+  assertPaths(^.outer.build.millSourcePath, thisPath / os.up / 'outer )
+  assertPaths(^.outer.build.sub.selfPath(), thisPath / os.up / 'outer / 'sub)
+  assertPaths(^.outer.build.sub.sub.selfPath(), thisPath / os.up / 'outer / 'sub / 'sub)
 }
 
 def checkOuterInnerPaths = T {
-  val thisPath : Path = millSourcePath
-  assertPaths(^.outer.inner.build.millSourcePath, thisPath / up / 'outer / 'inner )
-  assertPaths(^.outer.inner.build.sub.selfPath(), thisPath / up / 'outer / 'inner /'sub)
-  assertPaths(^.outer.inner.build.sub.sub.selfPath(), thisPath / up / 'outer / 'inner / 'sub / 'sub)
+  val thisPath : os.Path = millSourcePath
+  assertPaths(^.outer.inner.build.millSourcePath, thisPath / os.up / 'outer / 'inner )
+  assertPaths(^.outer.inner.build.sub.selfPath(), thisPath / os.up / 'outer / 'inner /'sub)
+  assertPaths(^.outer.inner.build.sub.sub.selfPath(), thisPath / os.up / 'outer / 'inner / 'sub / 'sub)
 }
 
 def checkProjectDests = T {
-  val outPath : Path = millSourcePath / 'out
+  val outPath : os.Path = millSourcePath / 'out
   assertPaths(sub.selfDest(), outPath / 'sub)
   assertPaths(sub.sub.selfDest(), outPath / 'sub / 'sub)
   assertPaths(sub.sub2.selfDest(), outPath / 'sub / 'sub2)
 }
 
 def checkInnerDests = T {
-  val foreignOut : Path = millSourcePath / 'out / "foreign-modules"
+  val foreignOut : os.Path = millSourcePath / 'out / "foreign-modules"
   assertPaths(inner.build.sub.selfDest(), foreignOut / 'inner / 'sub)
   assertPaths(inner.build.sub.sub.selfDest(), foreignOut / 'inner / 'sub / 'sub)
 }
 
 def checkOuterDests = T {
-  val foreignOut : Path = millSourcePath / 'out / "foreign-modules"
+  val foreignOut : os.Path = millSourcePath / 'out / "foreign-modules"
   assertPaths(^.outer.build.sub.selfDest(), foreignOut / "up-1" / 'outer/ 'sub )
   assertPaths(^.outer.build.sub.sub.selfDest(), foreignOut / "up-1" / 'outer/ 'sub / 'sub)
 }
 
 def checkOuterInnerDests = T {
-  val foreignOut : Path = millSourcePath / 'out / "foreign-modules"
+  val foreignOut : os.Path = millSourcePath / 'out / "foreign-modules"
   assertPaths(^.outer.inner.build.sub.selfDest(), foreignOut / "up-1" / 'outer/ 'inner / 'sub)
   assertPaths(^.outer.inner.build.sub.sub.selfDest(), foreignOut / "up-1" / 'outer/ 'inner / 'sub / 'sub)
 }
@@ -77,6 +76,6 @@ trait PathAware extends mill.Module {
 }
 
 trait DestAware extends mill.Module {
-  def selfDest = T { T.ctx().dest / up / up }
+  def selfDest = T { T.ctx().dest / os.up / os.up }
 }
 
diff --git a/main/test/resources/examples/foreign/project/inner/build.sc b/main/test/resources/examples/foreign/project/inner/build.sc
index 2d978292..da103b95 100644
--- a/main/test/resources/examples/foreign/project/inner/build.sc
+++ b/main/test/resources/examples/foreign/project/inner/build.sc
@@ -1,12 +1,11 @@
 import mill._
-import ammonite.ops._
 
 trait PathAware extends mill.Module {
   def selfPath = T { millSourcePath }
 }
 
 trait DestAware extends mill.Module {
-  def selfDest = T { T.ctx().dest / up / up }
+  def selfDest = T { T.ctx().dest / os.up / os.up }
 }
 
 object sub extends PathAware with DestAware {
diff --git a/main/test/resources/examples/javac/build.sc b/main/test/resources/examples/javac/build.sc
index 0783ac17..c45a6e2d 100644
--- a/main/test/resources/examples/javac/build.sc
+++ b/main/test/resources/examples/javac/build.sc
@@ -1,4 +1,3 @@
-import ammonite.ops._
 import mill.T
 import mill.eval.JavaCompileJarTests.compileAll
 import mill.eval.PathRef
@@ -14,10 +13,10 @@ def resourceRootPath = millSourcePath / 'resources
 //           resourceRoot ---->  jar
 def sourceRoot = T.sources{ sourceRootPath }
 def resourceRoot = T.sources{ resourceRootPath }
-def allSources = T{ sourceRoot().flatMap(p => ls.rec(p.path)).map(PathRef(_)) }
+def allSources = T{ sourceRoot().flatMap(p => os.walk(p.path)).map(PathRef(_)) }
 def classFiles = T{ compileAll(allSources()) }
 def jar = T{ Jvm.createJar(Loose.Agg(classFiles().path) ++ resourceRoot().map(_.path)) }
 
 def run(mainClsName: String) = T.command{
-  %%('java, "-cp", classFiles().path, mainClsName)(T.ctx().dest)
+  os.proc('java, "-cp", classFiles().path, mainClsName).call(T.ctx().dest)
 }
diff --git a/main/test/src/mill/UTestFramework.scala b/main/test/src/mill/UTestFramework.scala
index 6c0d5191..c234151b 100644
--- a/main/test/src/mill/UTestFramework.scala
+++ b/main/test/src/mill/UTestFramework.scala
@@ -5,7 +5,7 @@ class UTestFramework extends utest.runner.Framework {
     s.getClassName.startsWith("mill.")
   }
   override def setup() = {
-    import ammonite.ops._
-    rm(pwd / 'target / 'workspace)
+
+    os.remove.all(os.pwd / 'target / 'workspace)
   }
 }
diff --git a/main/test/src/mill/define/BasePathTests.scala b/main/test/src/mill/define/BasePathTests.scala
index d5167081..b8a653c8 100644
--- a/main/test/src/mill/define/BasePathTests.scala
+++ b/main/test/src/mill/define/BasePathTests.scala
@@ -2,7 +2,6 @@ package mill.define
 
 import mill.util.{TestGraphs, TestUtil}
 import utest._
-import ammonite.ops._
 import mill.{Module, T}
 object BasePathTests extends TestSuite{
   val testGraphs = new TestGraphs
@@ -54,7 +53,7 @@ object BasePathTests extends TestSuite{
     }
     'overriden - {
       object overridenBasePath extends TestUtil.BaseModule {
-        override def millSourcePath = pwd / 'overridenBasePathRootValue
+        override def millSourcePath = os.pwd / 'overridenBasePathRootValue
         object nested extends Module{
           override def millSourcePath = super.millSourcePath / 'overridenBasePathNested
           object nested extends Module{
@@ -63,9 +62,9 @@ object BasePathTests extends TestSuite{
         }
       }
       assert(
-        overridenBasePath.millSourcePath == pwd / 'overridenBasePathRootValue,
-        overridenBasePath.nested.millSourcePath == pwd / 'overridenBasePathRootValue / 'nested / 'overridenBasePathNested,
-        overridenBasePath.nested.nested.millSourcePath == pwd / 'overridenBasePathRootValue / 'nested / 'overridenBasePathNested / 'nested / 'overridenBasePathDoubleNested
+        overridenBasePath.millSourcePath == os.pwd / 'overridenBasePathRootValue,
+        overridenBasePath.nested.millSourcePath == os.pwd / 'overridenBasePathRootValue / 'nested / 'overridenBasePathNested,
+        overridenBasePath.nested.nested.millSourcePath == os.pwd / 'overridenBasePathRootValue / 'nested / 'overridenBasePathNested / 'nested / 'overridenBasePathDoubleNested
       )
     }
 
diff --git a/main/test/src/mill/define/CacherTests.scala b/main/test/src/mill/define/CacherTests.scala
index 98f2b7f8..84a8d840 100644
--- a/main/test/src/mill/define/CacherTests.scala
+++ b/main/test/src/mill/define/CacherTests.scala
@@ -1,6 +1,5 @@
 package mill.define
 
-import ammonite.ops.pwd
 import mill.util.{DummyLogger, TestEvaluator, TestUtil}
 import mill.util.Strict.Agg
 import mill.T
diff --git a/main/test/src/mill/eval/CrossTests.scala b/main/test/src/mill/eval/CrossTests.scala
index 3dec0222..f194924e 100644
--- a/main/test/src/mill/eval/CrossTests.scala
+++ b/main/test/src/mill/eval/CrossTests.scala
@@ -1,6 +1,6 @@
 package mill.eval
 
-import ammonite.ops._
+
 import mill.define.Discover
 import mill.util.TestEvaluator
 
diff --git a/main/test/src/mill/eval/EvaluationTests.scala b/main/test/src/mill/eval/EvaluationTests.scala
index 75a5bbe3..74f9088c 100644
--- a/main/test/src/mill/eval/EvaluationTests.scala
+++ b/main/test/src/mill/eval/EvaluationTests.scala
@@ -9,7 +9,7 @@ import mill.util.Strict.Agg
 import utest._
 import utest.framework.TestPath
 
-import ammonite.ops._
+
 
 object EvaluationTests extends TestSuite{
   class Checker[T <: TestUtil.BaseModule](module: T)(implicit tp: TestPath) {
diff --git a/main/test/src/mill/eval/FailureTests.scala b/main/test/src/mill/eval/FailureTests.scala
index 22021079..bf45119c 100644
--- a/main/test/src/mill/eval/FailureTests.scala
+++ b/main/test/src/mill/eval/FailureTests.scala
@@ -1,7 +1,6 @@
 package mill.eval
 import mill.T
 import mill.util.{TestEvaluator, TestUtil}
-import ammonite.ops.{Path, pwd, rm}
 import mill.eval.Result.OuterStack
 import utest._
 import utest.framework.TestPath
diff --git a/main/test/src/mill/eval/JavaCompileJarTests.scala b/main/test/src/mill/eval/JavaCompileJarTests.scala
index d4bdbd87..8e931747 100644
--- a/main/test/src/mill/eval/JavaCompileJarTests.scala
+++ b/main/test/src/mill/eval/JavaCompileJarTests.scala
@@ -1,7 +1,5 @@
 package mill.eval
 
-import ammonite.ops.ImplicitWd._
-import ammonite.ops._
 import mill.define.{Discover, Input, Target, Task}
 import mill.modules.Jvm
 import mill.util.Ctx.Dest
@@ -12,19 +10,19 @@ import utest._
 import mill._
 object JavaCompileJarTests extends TestSuite{
   def compileAll(sources: mill.util.Loose.Agg[PathRef])(implicit ctx: Dest) = {
-    mkdir(ctx.dest)
-    import ammonite.ops._
-    %("javac", sources.map(_.path.toString()).toSeq, "-d", ctx.dest)(wd = ctx.dest)
+    os.makeDir.all(ctx.dest)
+
+    os.proc("javac", sources.map(_.path.toString()).toSeq, "-d", ctx.dest).call(ctx.dest)
     PathRef(ctx.dest)
   }
 
   val tests = Tests{
     'javac {
-      val javacSrcPath = pwd / 'main / 'test / 'resources / 'examples / 'javac
+      val javacSrcPath = os.pwd / 'main / 'test / 'resources / 'examples / 'javac
       val javacDestPath =  TestUtil.getOutPath() / 'src
 
-      mkdir(javacDestPath / up)
-      cp(javacSrcPath, javacDestPath)
+      os.makeDir.all(javacDestPath / os.up)
+      os.copy(javacSrcPath, javacDestPath)
 
       object Build extends TestUtil.BaseModule{
         def sourceRootPath = javacDestPath / 'src
@@ -36,14 +34,14 @@ object JavaCompileJarTests extends TestSuite{
         //           resourceRoot ---->  jar
         def sourceRoot = T.sources{ sourceRootPath }
         def resourceRoot = T.sources{ resourceRootPath }
-        def allSources = T{ sourceRoot().flatMap(p => ls.rec(p.path)).map(PathRef(_)) }
+        def allSources = T{ sourceRoot().flatMap(p => os.walk(p.path)).map(PathRef(_)) }
         def classFiles = T{ compileAll(allSources()) }
         def jar = T{ Jvm.createJar(Loose.Agg(classFiles().path) ++ resourceRoot().map(_.path)) }
         // Test createJar() with optional file filter.
-        def filterJar(fileFilter: (Path, RelPath) => Boolean) = T{ Jvm.createJar(Loose.Agg(classFiles().path) ++ resourceRoot().map(_.path), None, fileFilter) }
+        def filterJar(fileFilter: (os.Path, os.RelPath) => Boolean) = T{ Jvm.createJar(Loose.Agg(classFiles().path) ++ resourceRoot().map(_.path), None, fileFilter) }
 
         def run(mainClsName: String) = T.command{
-          %%('java, "-Duser.language=en", "-cp", classFiles().path, mainClsName)
+          os.proc('java, "-Duser.language=en", "-cp", classFiles().path, mainClsName).call()
         }
       }
 
@@ -57,7 +55,7 @@ object JavaCompileJarTests extends TestSuite{
         evaluator.check(targets, expected)
       }
 
-      def append(path: Path, txt: String) = ammonite.ops.write.append(path, txt)
+      def append(path: os.Path, txt: String) = ammonite.ops.write.append(path, txt)
 
 
       check(
@@ -67,7 +65,6 @@ object JavaCompileJarTests extends TestSuite{
 
       // Re-running with no changes results in nothing being evaluated
       check(targets = Agg(jar), expected = Agg())
-
       // Appending an empty string gets ignored due to file-content hashing
       append(sourceRootPath / "Foo.java", "")
       check(targets = Agg(jar), expected = Agg())
@@ -106,7 +103,7 @@ object JavaCompileJarTests extends TestSuite{
       check(targets = Agg(allSources), expected = Agg(allSources))
       check(targets = Agg(jar), expected = Agg(classFiles, jar))
 
-      val jarContents = %%('jar, "-tf", evaluator.outPath/'jar/'dest/"out.jar")(evaluator.outPath).out.string
+      val jarContents = os.proc('jar, "-tf", evaluator.outPath/'jar/'dest/"out.jar").call(evaluator.outPath).out.string
       val expectedJarContents =
         """META-INF/MANIFEST.MF
           |test/Bar.class
@@ -116,16 +113,16 @@ object JavaCompileJarTests extends TestSuite{
           |test/FooTwo.class
           |hello.txt
           |""".stripMargin
-      assert(jarContents.lines.toSeq == expectedJarContents.lines.toSeq)
+      assert(jarContents.linesIterator.toSeq == expectedJarContents.linesIterator.toSeq)
 
       // Create the Jar again, but this time, filter out the Foo files.
       def noFoos(s: String) = !s.contains("Foo")
-      val filterFunc = (p: Path, r: RelPath) => noFoos(r.last)
+      val filterFunc = (p: os.Path, r: os.RelPath) => noFoos(r.last)
       eval(filterJar(filterFunc))
-      val filteredJarContents = %%('jar, "-tf", evaluator.outPath/'filterJar/'dest/"out.jar")(evaluator.outPath).out.string
-      assert(filteredJarContents.lines.toSeq == expectedJarContents.lines.filter(noFoos(_)).toSeq)
+      val filteredJarContents = os.proc('jar, "-tf", evaluator.outPath/'filterJar/'dest/"out.jar").call(evaluator.outPath).out.string
+      assert(filteredJarContents.linesIterator.toSeq == expectedJarContents.linesIterator.filter(noFoos(_)).toSeq)
 
-      val executed = %%('java, "-cp", evaluator.outPath/'jar/'dest/"out.jar", "test.Foo")(evaluator.outPath).out.string
+      val executed = os.proc('java, "-cp", evaluator.outPath/'jar/'dest/"out.jar", "test.Foo").call(evaluator.outPath).out.string
       assert(executed == (31337 + 271828) + System.lineSeparator)
 
       for(i <- 0 until 3){
diff --git a/main/test/src/mill/eval/ModuleTests.scala b/main/test/src/mill/eval/ModuleTests.scala
index 0b4a7c80..f28fc9b6 100644
--- a/main/test/src/mill/eval/ModuleTests.scala
+++ b/main/test/src/mill/eval/ModuleTests.scala
@@ -1,6 +1,6 @@
 package mill.eval
 
-import ammonite.ops._
+
 import mill.util.{TestEvaluator, TestUtil}
 import mill.T
 import mill.define.Discover
@@ -19,15 +19,15 @@ object ModuleTests extends TestSuite{
     def z = T{ ExternalModule.x() + ExternalModule.inner.y() }
   }
   val tests = Tests {
-    rm(TestEvaluator.externalOutPath)
+    os.remove.all(TestEvaluator.externalOutPath)
     'externalModuleTargetsAreNamespacedByModulePackagePath - {
       val check = new TestEvaluator(Build)
       val zresult = check.apply(Build.z)
       assert(
         zresult == Right((30, 1)),
-        read(check.evaluator.outPath / 'z / "meta.json").contains("30"),
-        read(TestEvaluator.externalOutPath / 'mill / 'eval / 'ModuleTests / 'ExternalModule / 'x / "meta.json").contains("13"),
-        read(TestEvaluator.externalOutPath / 'mill / 'eval / 'ModuleTests / 'ExternalModule / 'inner / 'y / "meta.json").contains("17")
+        os.read(check.evaluator.outPath / 'z / "meta.json").contains("30"),
+        os.read(TestEvaluator.externalOutPath / 'mill / 'eval / 'ModuleTests / 'ExternalModule / 'x / "meta.json").contains("13"),
+        os.read(TestEvaluator.externalOutPath / 'mill / 'eval / 'ModuleTests / 'ExternalModule / 'inner / 'y / "meta.json").contains("17")
       )
     }
     'externalModuleMustBeGlobalStatic - {
diff --git a/main/test/src/mill/eval/TaskTests.scala b/main/test/src/mill/eval/TaskTests.scala
index 4ba65e17..0bfd8efc 100644
--- a/main/test/src/mill/eval/TaskTests.scala
+++ b/main/test/src/mill/eval/TaskTests.scala
@@ -1,7 +1,7 @@
 package mill.eval
 
 import utest._
-import ammonite.ops._
+
 import mill.T
 
 import mill.util.TestEvaluator
@@ -34,15 +34,15 @@ object TaskTests extends TestSuite{
 
       def persistent = T.persistent{
         input() // force re-computation
-        mkdir(T.ctx().dest)
-        write.append(T.ctx().dest/'count, "hello\n")
-        read.lines(T.ctx().dest/'count).length
+        os.makeDir.all(T.ctx().dest)
+        os.write.append(T.ctx().dest/'count, "hello\n")
+        os.read.lines(T.ctx().dest/'count).length
       }
       def nonPersistent = T{
         input() // force re-computation
-        mkdir(T.ctx().dest)
-        write.append(T.ctx().dest/'count, "hello\n")
-        read.lines(T.ctx().dest/'count).length
+        os.makeDir.all(T.ctx().dest)
+        os.write.append(T.ctx().dest/'count, "hello\n")
+        os.read.lines(T.ctx().dest/'count).length
       }
 
       def staticWorkerDownstream = T{
diff --git a/main/test/src/mill/main/ClientServerTests.scala b/main/test/src/mill/main/ClientServerTests.scala
index 2462f650..05238a5f 100644
--- a/main/test/src/mill/main/ClientServerTests.scala
+++ b/main/test/src/mill/main/ClientServerTests.scala
@@ -1,6 +1,5 @@
 package mill.main
 import java.io._
-import java.nio.file.Path
 
 import mill.main.client.{Util, Locks}
 
@@ -47,7 +46,7 @@ object ClientServerTests extends TestSuite{
     (tmpDir, locks)
   }
 
-  def spawnEchoServer(tmpDir : Path, locks: Locks): Unit = {
+  def spawnEchoServer(tmpDir : java.nio.file.Path, locks: Locks): Unit = {
     new Thread(() => new Server(
       tmpDir.toString,
       new EchoServer(),
@@ -57,7 +56,7 @@ object ClientServerTests extends TestSuite{
     ).run()).start()
   }
 
-  def runClientAux(tmpDir : Path, locks: Locks)
+  def runClientAux(tmpDir : java.nio.file.Path, locks: Locks)
                   (env : Map[String, String], args: Array[String]) = {
     val (in, out, err) = initStreams()
     Server.lockBlock(locks.clientLock){
diff --git a/main/test/src/mill/main/ForeignBuildsTest.scala b/main/test/src/mill/main/ForeignBuildsTest.scala
index 085ada02..cfc8d00c 100644
--- a/main/test/src/mill/main/ForeignBuildsTest.scala
+++ b/main/test/src/mill/main/ForeignBuildsTest.scala
@@ -1,14 +1,13 @@
 package mill.main
 
-import ammonite.ops._
 import mill.util.ScriptTestSuite
 import utest._
 
 object ForeignBuildsTest extends ScriptTestSuite(fork = false) {
   def workspaceSlug = "foreign-builds"
   def scriptSourcePath =
-    pwd / 'main / 'test / 'resources / 'examples / 'foreign
-  override def buildPath = 'project / "build.sc"
+    os.pwd / 'main / 'test / 'resources / 'examples / 'foreign
+  override def buildPath = os.rel / 'project / "build.sc"
 
   val tests = Tests {
     initWorkspace()
diff --git a/main/test/src/mill/main/ForeignConflictTest.scala b/main/test/src/mill/main/ForeignConflictTest.scala
index c5d99c9f..a4352bb6 100644
--- a/main/test/src/mill/main/ForeignConflictTest.scala
+++ b/main/test/src/mill/main/ForeignConflictTest.scala
@@ -1,14 +1,14 @@
 package mill.main
 
-import ammonite.ops._
+
 import mill.util.ScriptTestSuite
 import utest._
 
 object ForeignConflictTest extends ScriptTestSuite(fork = false) {
   def workspaceSlug = "foreign-conflict"
   def scriptSourcePath =
-    pwd / 'main / 'test / 'resources / 'examples / 'foreign
-  override def buildPath = 'conflict / "build.sc"
+    os.pwd / 'main / 'test / 'resources / 'examples / 'foreign
+  override def buildPath = os.rel / 'conflict / "build.sc"
 
   val tests = Tests {
     initWorkspace()
diff --git a/main/test/src/mill/main/JavaCompileJarTests.scala b/main/test/src/mill/main/JavaCompileJarTests.scala
index 6c45b454..37c64b05 100644
--- a/main/test/src/mill/main/JavaCompileJarTests.scala
+++ b/main/test/src/mill/main/JavaCompileJarTests.scala
@@ -1,12 +1,11 @@
 package mill.main
 
-import ammonite.ops._
 import mill.util.ScriptTestSuite
 import utest._
 
 object JavaCompileJarTests extends ScriptTestSuite(fork = false) {
   def workspaceSlug = "java-compile-jar"
-  def scriptSourcePath = pwd / 'main / 'test / 'resources / 'examples / 'javac
+  def scriptSourcePath = os.pwd / 'main / 'test / 'resources / 'examples / 'javac
   val tests = Tests{
     initWorkspace()
     'test - {
@@ -31,8 +30,8 @@ object JavaCompileJarTests extends ScriptTestSuite(fork = false) {
         )
 
         // If we update resources, classFiles are unchanged but jar changes
-        for(scalaFile <- ls.rec(workspacePath).filter(_.ext == "txt")){
-          write.append(scalaFile, "\n")
+        for(scalaFile <- os.walk(workspacePath).filter(_.ext == "txt")){
+          os.write.append(scalaFile, "\n")
         }
 
         assert(eval("classFiles"))
@@ -48,15 +47,15 @@ object JavaCompileJarTests extends ScriptTestSuite(fork = false) {
 
         // We can intentionally break the code, have the targets break, then
         // fix the code and have them recover.
-        for(scalaFile <- ls.rec(workspacePath).filter(_.ext == "java")){
-          write.append(scalaFile, "\n}")
+        for(scalaFile <- os.walk(workspacePath).filter(_.ext == "java")){
+          os.write.append(scalaFile, "\n}")
         }
 
         assert(!eval("classFiles"))
         assert(!eval("jar"))
 
-        for(scalaFile <- ls.rec(workspacePath).filter(_.ext == "java")){
-          write.over(scalaFile, read(scalaFile).dropRight(2))
+        for(scalaFile <- os.walk(workspacePath).filter(_.ext == "java")){
+          os.write.over(scalaFile, os.read(scalaFile).dropRight(2))
         }
 
         assert(eval("classFiles"))
diff --git a/main/test/src/mill/util/ScriptTestSuite.scala b/main/test/src/mill/util/ScriptTestSuite.scala
index 9d3edb65..b324f94c 100644
--- a/main/test/src/mill/util/ScriptTestSuite.scala
+++ b/main/test/src/mill/util/ScriptTestSuite.scala
@@ -2,16 +2,15 @@ package mill.util
 
 import java.io.{ByteArrayInputStream, ByteArrayOutputStream, PrintStream}
 
-import ammonite.ops._
 import utest._
 
 abstract class ScriptTestSuite(fork: Boolean) extends TestSuite{
   def workspaceSlug: String
-  def scriptSourcePath: Path
-  def buildPath: RelPath = "build.sc"
+  def scriptSourcePath: os.Path
+  def buildPath: os.RelPath = "build.sc"
 
-  val workspacePath = pwd / 'target / 'workspace / workspaceSlug
-  val wd = workspacePath / buildPath / up
+  val workspacePath = os.pwd / 'target / 'workspace / workspaceSlug
+  val wd = workspacePath / buildPath / os.up
   val stdOutErr = new PrintStream(new ByteArrayOutputStream())
   val stdIn = new ByteArrayInputStream(Array())
   val disableTicker = false
@@ -25,7 +24,7 @@ abstract class ScriptTestSuite(fork: Boolean) extends TestSuite{
     if (!fork) runner.runScript(workspacePath / buildPath , s.toList)
     else{
       try {
-        %(home / "mill-release", "-i", s)(wd)
+        os.proc(os.home / "mill-release", "-i", s).call(wd)
         true
       }catch{case e: Throwable => false}
     }
@@ -33,17 +32,17 @@ abstract class ScriptTestSuite(fork: Boolean) extends TestSuite{
   def meta(s: String) = {
     val (List(selector), args) = ParseArgs.apply(Seq(s), multiSelect = false).right.get
 
-    read(wd / "out" / selector._2.value.flatMap(_.pathSegments) / "meta.json")
+    os.read(wd / "out" / selector._2.value.flatMap(_.pathSegments) / "meta.json")
   }
 
 
   def initWorkspace() = {
-    rm(workspacePath)
-    mkdir(workspacePath / up)
+    os.remove.all(workspacePath)
+    os.makeDir.all(workspacePath / os.up)
     // The unzipped git repo snapshots we get from github come with a
     // wrapper-folder inside the zip file, so copy the wrapper folder to the
     // destination instead of the folder containing the wrapper.
 
-    cp(scriptSourcePath, workspacePath)
+    os.copy(scriptSourcePath, workspacePath)
   }
 }
diff --git a/main/test/src/mill/util/TestEvaluator.scala b/main/test/src/mill/util/TestEvaluator.scala
index 6e7fe484..67ba96dc 100644
--- a/main/test/src/mill/util/TestEvaluator.scala
+++ b/main/test/src/mill/util/TestEvaluator.scala
@@ -1,6 +1,5 @@
 package mill.util
 
-import ammonite.ops.pwd
 import mill.define.{Input, Target, Task}
 import mill.eval.Result.OuterStack
 import mill.eval.{Evaluator, Result}
@@ -10,7 +9,7 @@ import utest.framework.TestPath
 
 import language.experimental.macros
 object TestEvaluator{
-  val externalOutPath = pwd / 'target / 'external
+  val externalOutPath = os.pwd / 'target / 'external
 
 
   def static(module: TestUtil.BaseModule)(implicit fullName: sourcecode.FullName) = {
diff --git a/main/test/src/mill/util/TestUtil.scala b/main/test/src/mill/util/TestUtil.scala
index b4e3af89..e5fe906e 100644
--- a/main/test/src/mill/util/TestUtil.scala
+++ b/main/test/src/mill/util/TestUtil.scala
@@ -1,7 +1,6 @@
 package mill.util
 
 import mill.util.Router.Overrides
-import ammonite.ops.pwd
 import mill.define._
 import mill.eval.Result
 import mill.eval.Result.OuterStack
@@ -14,17 +13,17 @@ import scala.collection.mutable
 object TestUtil {
   def getOutPath()(implicit fullName: sourcecode.FullName,
                    tp: TestPath) = {
-    pwd / 'target / 'workspace / (fullName.value.split('.') ++ tp.value)
+    os.pwd / 'target / 'workspace / (fullName.value.split('.') ++ tp.value)
   }
   def getOutPathStatic()(implicit fullName: sourcecode.FullName) = {
-    pwd / 'target / 'workspace / fullName.value.split('.')
+    os.pwd / 'target / 'workspace / fullName.value.split('.')
   }
 
   def getSrcPathStatic()(implicit fullName: sourcecode.FullName) = {
-    pwd / 'target / 'worksources / fullName.value.split('.')
+    os.pwd / 'target / 'worksources / fullName.value.split('.')
   }
   def getSrcPathBase() = {
-    pwd / 'target / 'worksources
+    os.pwd / 'target / 'worksources
   }
 
   class BaseModule(implicit millModuleEnclosing0: sourcecode.Enclosing,
diff --git a/readme.md b/readme.md
index dd05d0c0..a87fba0d 100644
--- a/readme.md
+++ b/readme.md
@@ -117,7 +117,7 @@ In case of troubles with caching and/or incremental compilation, you can always
 restart from scratch removing the `out` directory:
 
 ```bash
-rm -rf out/
+os.remove.all -rf out/
 ```
 
 ## Project Layout
diff --git a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
index e0ee55a5..37537a85 100644
--- a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
+++ b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
@@ -1,7 +1,6 @@
 package mill
 package scalajslib
 
-import ammonite.ops.{Path, exists, ls, mkdir, rm}
 import coursier.Cache
 import coursier.maven.MavenRepository
 import mill.eval.{PathRef, Result}
@@ -108,13 +107,13 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
            moduleKind: ModuleKind)(implicit ctx: Ctx): Result[PathRef] = {
     val outputPath = ctx.dest / "out.js"
 
-    mkdir(ctx.dest)
-    rm(outputPath)
+    os.makeDir.all(ctx.dest)
+    os.remove.all(outputPath)
 
     val classpath = runClasspath.map(_.path)
     val sjsirFiles = classpath
-      .filter(path => exists(path) && path.isDir)
-      .flatMap(ls.rec)
+      .filter(path => os.exists(path) && os.isDir(path))
+      .flatMap(os.walk(_))
       .filter(_.ext == "sjsir")
     val libraries = classpath.filter(_.ext == "jar")
     worker.link(
diff --git a/scalajslib/src/mill/scalajslib/ScalaJSWorkerApi.scala b/scalajslib/src/mill/scalajslib/ScalaJSWorkerApi.scala
index 552aa572..881a65b9 100644
--- a/scalajslib/src/mill/scalajslib/ScalaJSWorkerApi.scala
+++ b/scalajslib/src/mill/scalajslib/ScalaJSWorkerApi.scala
@@ -3,7 +3,6 @@ package mill.scalajslib
 import java.io.File
 import java.net.URLClassLoader
 
-import ammonite.ops.Path
 import mill.define.Discover
 import mill.eval.Result
 import mill.util.Ctx
@@ -23,10 +22,10 @@ object ModuleKind{
 class ScalaJSWorker {
   private var scalaInstanceCache = Option.empty[(Long, ScalaJSWorkerApi)]
 
-  private def bridge(toolsClasspath: Agg[Path])
+  private def bridge(toolsClasspath: Agg[os.Path])
                     (implicit ctx: Ctx.Home) = {
     val classloaderSig =
-      toolsClasspath.map(p => p.toString().hashCode + p.mtime.toMillis).sum
+      toolsClasspath.map(p => p.toString().hashCode + os.mtime(p)).sum
     scalaInstanceCache match {
       case Some((sig, bridge)) if sig == classloaderSig => bridge
       case _ =>
@@ -44,14 +43,14 @@ class ScalaJSWorker {
     }
   }
 
-  def link(toolsClasspath: Agg[Path],
-           sources: Agg[Path],
-           libraries: Agg[Path],
+  def link(toolsClasspath: Agg[os.Path],
+           sources: Agg[os.Path],
+           libraries: Agg[os.Path],
            dest: File,
            main: Option[String],
            fullOpt: Boolean,
            moduleKind: ModuleKind)
-          (implicit ctx: Ctx.Home): Result[Path] = {
+          (implicit ctx: Ctx.Home): Result[os.Path] = {
     bridge(toolsClasspath).link(
       sources.items.map(_.toIO).toArray,
       libraries.items.map(_.toIO).toArray,
@@ -59,15 +58,15 @@ class ScalaJSWorker {
       main.orNull,
       fullOpt,
       moduleKind
-    ).map(Path(_))
+    ).map(os.Path(_))
   }
 
-  def run(toolsClasspath: Agg[Path], config: NodeJSConfig, linkedFile: File)
+  def run(toolsClasspath: Agg[os.Path], config: NodeJSConfig, linkedFile: File)
          (implicit ctx: Ctx.Home): Unit = {
     bridge(toolsClasspath).run(config, linkedFile)
   }
 
-  def getFramework(toolsClasspath: Agg[Path],
+  def getFramework(toolsClasspath: Agg[os.Path],
                    config: NodeJSConfig,
                    frameworkName: String,
                    linkedFile: File)
diff --git a/scalajslib/test/src/mill/scalajslib/HelloJSWorldTests.scala b/scalajslib/test/src/mill/scalajslib/HelloJSWorldTests.scala
index cfdcdd1f..7b1027e8 100644
--- a/scalajslib/test/src/mill/scalajslib/HelloJSWorldTests.scala
+++ b/scalajslib/test/src/mill/scalajslib/HelloJSWorldTests.scala
@@ -1,8 +1,6 @@
 package mill.scalajslib
 
 import java.util.jar.JarFile
-
-import ammonite.ops._
 import mill._
 import mill.define.Discover
 import mill.eval.{Evaluator, Result}
@@ -71,7 +69,7 @@ object HelloJSWorldTests extends TestSuite {
     override lazy val millDiscover = Discover[this.type]
   }
 
-  val millSourcePath = pwd / 'scalajslib / 'test / 'resources / "hello-js-world"
+  val millSourcePath = os.pwd / 'scalajslib / 'test / 'resources / "hello-js-world"
 
   val helloWorldEvaluator = TestEvaluator.static(HelloJSWorld)
 
@@ -87,7 +85,7 @@ object HelloJSWorldTests extends TestSuite {
           helloWorldEvaluator(HelloJSWorld.helloJsWorld(scalaVersion, scalaJSVersion).compile)
 
         val outPath = result.classes.path
-        val outputFiles = ls.rec(outPath)
+        val outputFiles = os.walk(outPath)
         val expectedClassfiles = compileClassfiles(outPath)
         assert(
           outputFiles.toSet == expectedClassfiles,
@@ -213,7 +211,7 @@ object HelloJSWorldTests extends TestSuite {
         helloWorldEvaluator.outPath,
         task.ctx.segments
       )
-      val log = read(paths.log)
+      val log = os.read(paths.log)
       assert(
         evalCount > 0,
         log.contains("node"),
@@ -229,7 +227,7 @@ object HelloJSWorldTests extends TestSuite {
     }
   }
 
-  def compileClassfiles(parentDir: Path) = Set(
+  def compileClassfiles(parentDir: os.Path) = Set(
     parentDir / "ArgsParser$.class",
     parentDir / "ArgsParser$.sjsir",
     parentDir / "ArgsParser.class",
@@ -241,9 +239,9 @@ object HelloJSWorldTests extends TestSuite {
   )
 
   def prepareWorkspace(): Unit = {
-    rm(workspacePath)
-    mkdir(workspacePath / up)
-    cp(millSourcePath, workspacePath)
+    os.remove.all(workspacePath)
+    os.makeDir.all(workspacePath / os.up)
+    os.copy(millSourcePath, workspacePath)
   }
 
 }
diff --git a/scalajslib/test/src/mill/scalajslib/MultiModuleTests.scala b/scalajslib/test/src/mill/scalajslib/MultiModuleTests.scala
index 37429038..751c7537 100644
--- a/scalajslib/test/src/mill/scalajslib/MultiModuleTests.scala
+++ b/scalajslib/test/src/mill/scalajslib/MultiModuleTests.scala
@@ -1,6 +1,5 @@
 package mill.scalajslib
 
-import ammonite.ops._
 import mill._
 import mill.define.Discover
 import mill.eval.Evaluator
@@ -10,7 +9,7 @@ import utest._
 
 object MultiModuleTests extends TestSuite {
   val workspacePath =  TestUtil.getOutPathStatic() / "multi-module"
-  val sourcePath = pwd / 'scalajslib / 'test / 'resources / "multi-module"
+  val sourcePath = os.pwd / 'scalajslib / 'test / 'resources / "multi-module"
 
   object MultiModule extends TestUtil.BaseModule {
     trait BaseModule extends ScalaJSModule {
@@ -76,7 +75,7 @@ object MultiModuleTests extends TestSuite {
         evaluator.outPath,
         command.ctx.segments
       )
-      val log = read(paths.log)
+      val log = os.read(paths.log)
       assert(
         evalCount > 0,
         log.contains("node"),
@@ -86,9 +85,9 @@ object MultiModuleTests extends TestSuite {
   }
 
   def prepareWorkspace(): Unit = {
-    rm(workspacePath)
-    mkdir(workspacePath / up)
-    cp(sourcePath, workspacePath)
+    os.remove.all(workspacePath)
+    os.makeDir.all(workspacePath / os.up)
+    os.copy(sourcePath, workspacePath)
   }
 
 }
diff --git a/scalajslib/test/src/mill/scalajslib/NodeJSConfigTests.scala b/scalajslib/test/src/mill/scalajslib/NodeJSConfigTests.scala
index 5aef8dad..27ea0a13 100644
--- a/scalajslib/test/src/mill/scalajslib/NodeJSConfigTests.scala
+++ b/scalajslib/test/src/mill/scalajslib/NodeJSConfigTests.scala
@@ -1,6 +1,5 @@
 package mill.scalajslib
 
-import ammonite.ops._
 import mill._
 import mill.define.Discover
 import mill.eval.Evaluator
@@ -53,7 +52,7 @@ object NodeJSConfigTests extends TestSuite {
     override lazy val millDiscover = Discover[this.type]
   }
 
-  val millSourcePath = pwd / 'scalajslib / 'test / 'resources / "hello-js-world"
+  val millSourcePath = os.pwd / 'scalajslib / 'test / 'resources / "hello-js-world"
 
   val helloWorldEvaluator = TestEvaluator.static(HelloJSWorld)
 
@@ -68,7 +67,7 @@ object NodeJSConfigTests extends TestSuite {
         helloWorldEvaluator.outPath,
         command.ctx.segments
       )
-      val log = read(paths.log)
+      val log = os.read(paths.log)
       assert(
         nodeArgs.forall(log.contains),
         notNodeArgs.forall(!log.contains(_))
@@ -96,9 +95,9 @@ object NodeJSConfigTests extends TestSuite {
   }
 
   def prepareWorkspace(): Unit = {
-    rm(workspacePath)
-    mkdir(workspacePath / up)
-    cp(millSourcePath, workspacePath)
+    os.remove.all(workspacePath)
+    os.makeDir.all(workspacePath / os.up)
+    os.copy(millSourcePath, workspacePath)
   }
 
 }
diff --git a/scalajslib/test/src/mill/scalajslib/ScalaJsUtils.scala b/scalajslib/test/src/mill/scalajslib/ScalaJsUtils.scala
index 859d2d56..68f2f7ee 100644
--- a/scalajslib/test/src/mill/scalajslib/ScalaJsUtils.scala
+++ b/scalajslib/test/src/mill/scalajslib/ScalaJsUtils.scala
@@ -3,10 +3,8 @@ package mill.scalajslib
 import java.io.{FileReader, StringWriter}
 import javax.script.{ScriptContext, ScriptEngineManager}
 
-import ammonite.ops.Path
-
 object ScalaJsUtils {
-  def runJS(path: Path): String = {
+  def runJS(path: os.Path): String = {
     val engineManager = new ScriptEngineManager(null)
     val engine = engineManager.getEngineByName("nashorn")
     val console = new Console
diff --git a/scalalib/src/mill/scalalib/GenIdeaImpl.scala b/scalalib/src/mill/scalalib/GenIdeaImpl.scala
index b4f77f16..87b039df 100644
--- a/scalalib/src/mill/scalalib/GenIdeaImpl.scala
+++ b/scalalib/src/mill/scalalib/GenIdeaImpl.scala
@@ -1,6 +1,5 @@
 package mill.scalalib
 
-import ammonite.ops._
 import ammonite.runtime.SpecialClassLoader
 import coursier.{Cache, CoursierPaths, Repository}
 import mill.define._
@@ -34,21 +33,21 @@ object GenIdeaImpl {
             discover: Discover[_]): Unit = {
     val pp = new scala.xml.PrettyPrinter(999, 4)
 
-    val jdkInfo = extractCurrentJdk(pwd / ".idea" / "misc.xml").getOrElse(("JDK_1_8", "1.8 (1)"))
+    val jdkInfo = extractCurrentJdk(os.pwd / ".idea" / "misc.xml").getOrElse(("JDK_1_8", "1.8 (1)"))
 
-    rm! pwd/".idea"/"libraries"
-    rm! pwd/".idea"/"scala_compiler.xml"
-    rm! pwd/".idea_modules"
+    os.remove.all(os.pwd/".idea"/"libraries")
+    os.remove.all(os.pwd/".idea"/"scala_compiler.xml")
+    os.remove.all(os.pwd/".idea_modules")
 
 
-    val evaluator = new Evaluator(ctx.home, pwd / 'out, pwd / 'out, rootModule, ctx.log)
+    val evaluator = new Evaluator(ctx.home, os.pwd / 'out, os.pwd / 'out, rootModule, ctx.log)
 
     for((relPath, xml) <- xmlFileLayout(evaluator, rootModule, jdkInfo)){
-      write.over(pwd/relPath, pp.format(xml))
+      os.write.over(os.pwd/relPath, pp.format(xml))
     }
   }
 
-  def extractCurrentJdk(ideaPath: Path): Option[(String,String)] = {
+  def extractCurrentJdk(ideaPath: os.Path): Option[(String,String)] = {
     import scala.xml.XML
     Try {
       val xml = XML.loadFile(ideaPath.toString)
@@ -62,7 +61,7 @@ object GenIdeaImpl {
   def xmlFileLayout(evaluator: Evaluator,
                     rootModule: mill.Module,
                     jdkInfo: (String,String),
-                    fetchMillModules: Boolean = true): Seq[(RelPath, scala.xml.Node)] = {
+                    fetchMillModules: Boolean = true): Seq[(os.RelPath, scala.xml.Node)] = {
 
     val modules = rootModule.millInternal.segmentsToModules.values
       .collect{ case x: scalalib.JavaModule => (x.millModuleSegments, x)}
@@ -71,7 +70,7 @@ object GenIdeaImpl {
     val buildLibraryPaths =
       if (!fetchMillModules) Nil
       else sys.props.get("MILL_BUILD_LIBRARIES") match {
-        case Some(found) => found.split(',').map(Path(_)).distinct.toList
+        case Some(found) => found.split(',').map(os.Path(_)).distinct.toList
         case None =>
           val repos = modules.foldLeft(Set.empty[Repository]) { _ ++ _._2.repositories }
           val artifactNames = Seq("main-moduledefs", "main-core", "scalalib", "scalajslib")
@@ -91,7 +90,7 @@ object GenIdeaImpl {
       .asInstanceOf[SpecialClassLoader]
     ).map {
        _.allJars
-        .map(url => Path(url.getFile))
+        .map(url => os.Path(url.getFile))
         .filter(_.toIO.exists)
     }.getOrElse(Seq())
 
@@ -138,8 +137,8 @@ object GenIdeaImpl {
     val commonPrefix =
       if (allResolved.isEmpty) 0
       else {
-        val minResolvedLength = allResolved.map(_.segments.length).min
-        allResolved.map(_.segments.take(minResolvedLength))
+        val minResolvedLength = allResolved.map(_.segmentCount).min
+        allResolved.map(_.segments.take(minResolvedLength).toList)
           .transpose
           .takeWhile(_.distinct.length == 1)
           .length
@@ -148,37 +147,37 @@ object GenIdeaImpl {
     // only resort to full long path names if the jar name is a duplicate
     val pathShortLibNameDuplicate = allResolved
       .distinct
-      .map{p => p.segments.last -> p}
+      .map{p => p.last -> p}
       .groupBy(_._1)
       .filter(_._2.size > 1)
       .keySet
 
     val pathToLibName = allResolved
       .map{p =>
-        if (pathShortLibNameDuplicate(p.segments.last))
+        if (pathShortLibNameDuplicate(p.last))
           (p, p.segments.drop(commonPrefix).mkString("_"))
         else
-          (p, p.segments.last)
+          (p, p.last)
       }
       .toMap
 
-    sealed trait ResolvedLibrary { def path : Path }
-    case class CoursierResolved(path : Path, pom : Path, sources : Option[Path])
+    sealed trait ResolvedLibrary { def path : os.Path }
+    case class CoursierResolved(path : os.Path, pom : os.Path, sources : Option[os.Path])
       extends ResolvedLibrary
-    case class OtherResolved(path : Path) extends ResolvedLibrary
+    case class OtherResolved(path : os.Path) extends ResolvedLibrary
 
     // Tries to group jars with their poms and sources.
-    def toResolvedJar(path : Path) : Option[ResolvedLibrary] = {
-      val inCoursierCache = path.startsWith(Path(CoursierPaths.cacheDirectory()))
-      val isSource = path.segments.last.endsWith("sources.jar")
+    def toResolvedJar(path : os.Path) : Option[ResolvedLibrary] = {
+      val inCoursierCache = path.startsWith(os.Path(CoursierPaths.cacheDirectory()))
+      val isSource = path.last.endsWith("sources.jar")
       val isPom = path.ext == "pom"
       if (inCoursierCache && (isSource || isPom)) {
         // Remove sources and pom as they'll be recovered from the jar path
         None
       } else if (inCoursierCache && path.ext == "jar") {
-        val withoutExt = path.segments.last.dropRight(path.ext.length + 1)
-        val pom = path / up / s"$withoutExt.pom"
-        val sources = Some(path / up / s"$withoutExt-sources.jar")
+        val withoutExt = path.last.dropRight(path.ext.length + 1)
+        val pom = path / os.up / s"$withoutExt.pom"
+        val sources = Some(path / os.up / s"$withoutExt-sources.jar")
           .filter(_.toIO.exists())
         Some(CoursierResolved(path, pom, sources))
       } else Some(OtherResolved(path))
@@ -186,7 +185,7 @@ object GenIdeaImpl {
 
     // Hack so that Intellij does not complain about unresolved magic
     // imports in build.sc when in fact they are resolved
-    def sbtLibraryNameFromPom(pom : Path) : String = {
+    def sbtLibraryNameFromPom(pom : os.Path) : String = {
       val xml = scala.xml.XML.loadFile(pom.toIO)
 
       val groupId = (xml \ "groupId").text
@@ -206,12 +205,12 @@ object GenIdeaImpl {
         pathToLibName(path)
     }
 
-    def resolvedLibraries(resolved : Seq[Path]) : Seq[ResolvedLibrary] = resolved
+    def resolvedLibraries(resolved : Seq[os.Path]) : Seq[ResolvedLibrary] = resolved
       .map(toResolvedJar)
       .collect { case Some(r) => r}
 
     val compilerSettings = resolved
-      .foldLeft(Map[(Loose.Agg[Path], Seq[String]), Vector[JavaModule]]()) {
+      .foldLeft(Map[(Loose.Agg[os.Path], Seq[String]), Vector[JavaModule]]()) {
         (r, q) =>
           val key = (q._4, q._5)
           r + (key -> (r.getOrElse(key, Vector()) :+ q._3))
@@ -221,10 +220,10 @@ object GenIdeaImpl {
       resolvedLibraries(buildLibraryPaths ++ buildDepsPaths).toSet
 
     val fixedFiles = Seq(
-      Tuple2(".idea"/"misc.xml", miscXmlTemplate(jdkInfo)),
-      Tuple2(".idea"/"scala_settings.xml", scalaSettingsTemplate()),
+      Tuple2(os.rel/".idea"/"misc.xml", miscXmlTemplate(jdkInfo)),
+      Tuple2(os.rel/".idea"/"scala_settings.xml", scalaSettingsTemplate()),
       Tuple2(
-        ".idea"/"modules.xml",
+        os.rel/".idea"/"modules.xml",
         allModulesXmlTemplate(
           modules
             .filter(!_._2.skipIdea)
@@ -232,14 +231,14 @@ object GenIdeaImpl {
         )
       ),
       Tuple2(
-        ".idea_modules"/"mill-build.iml",
+        os.rel/".idea_modules"/"mill-build.iml",
         rootXmlTemplate(
           for(lib <- allBuildLibraries)
           yield libraryName(lib)
         )
       ),
       Tuple2(
-        ".idea"/"scala_compiler.xml",
+        os.rel/".idea"/"scala_compiler.xml",
         scalaCompilerTemplate(compilerSettings)
       )
     )
@@ -252,7 +251,7 @@ object GenIdeaImpl {
         case CoursierResolved(_, _, s) => s.map(p => "jar://" + p + "!/")
         case OtherResolved(_) => None
       }
-      Tuple2(".idea"/'libraries/s"$name.xml", libraryXmlTemplate(name, url, sources))
+      Tuple2(os.rel/".idea"/'libraries/s"$name.xml", libraryXmlTemplate(name, url, sources))
     }
 
     val moduleFiles = resolved.map{ case (path, resolvedDeps, mod, _, _) =>
@@ -293,7 +292,7 @@ object GenIdeaImpl {
         Strict.Agg.from(mod.moduleDeps.map{ m => moduleName(moduleLabels(m))}.distinct),
         isTest
       )
-      Tuple2(".idea_modules"/s"${moduleName(path)}.iml", elem)
+      Tuple2(os.rel/".idea_modules"/s"${moduleName(path)}.iml", elem)
     }
 
     fixedFiles ++ libraries ++ moduleFiles
@@ -306,8 +305,8 @@ object GenIdeaImpl {
     }
   }
 
-  def relify(p: Path) = {
-    val r = p.relativeTo(pwd/".idea_modules")
+  def relify(p: os.Path) = {
+    val r = p.relativeTo(os.pwd/".idea_modules")
     (Seq.fill(r.ups)("..") ++ r.segments).mkString("/")
   }
 
@@ -387,13 +386,13 @@ object GenIdeaImpl {
       </library>
     </component>
   }
-  def moduleXmlTemplate(basePath: Path,
+  def moduleXmlTemplate(basePath: os.Path,
                         scalaVersionOpt: Option[String],
-                        resourcePaths: Strict.Agg[Path],
-                        normalSourcePaths: Strict.Agg[Path],
-                        generatedSourcePaths: Strict.Agg[Path],
-                        compileOutputPath: Path,
-                        generatedSourceOutputPath: Path,
+                        resourcePaths: Strict.Agg[os.Path],
+                        normalSourcePaths: Strict.Agg[os.Path],
+                        generatedSourcePaths: Strict.Agg[os.Path],
+                        compileOutputPath: os.Path,
+                        generatedSourceOutputPath: os.Path,
                         libNames: Strict.Agg[String],
                         depNames: Strict.Agg[String],
                         isTest: Boolean
@@ -447,7 +446,7 @@ object GenIdeaImpl {
       </component>
     </module>
   }
-  def scalaCompilerTemplate(settings: Map[(Loose.Agg[Path], Seq[String]), Seq[JavaModule]]) = {
+  def scalaCompilerTemplate(settings: Map[(Loose.Agg[os.Path], Seq[String]), Seq[JavaModule]]) = {
 
     <project version="4">
       <component name="ScalaCompilerConfiguration">
diff --git a/scalalib/src/mill/scalalib/JavaModule.scala b/scalalib/src/mill/scalalib/JavaModule.scala
index 111cfdb2..387011ec 100644
--- a/scalalib/src/mill/scalalib/JavaModule.scala
+++ b/scalalib/src/mill/scalalib/JavaModule.scala
@@ -1,8 +1,6 @@
 package mill
 package scalalib
 
-
-import ammonite.ops._
 import coursier.Repository
 import mill.define.Task
 import mill.define.TaskModule
@@ -199,12 +197,12 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
     * All individual source files fed into the compiler
     */
   def allSourceFiles = T{
-    def isHiddenFile(path: Path) = path.segments.last.startsWith(".")
+    def isHiddenFile(path: os.Path) = path.last.startsWith(".")
     for {
       root <- allSources()
-      if exists(root.path)
-      path <- (if (root.path.isDir) ls.rec(root.path) else Seq(root.path))
-      if path.isFile && ((path.ext == "scala" || path.ext == "java") && !isHiddenFile(path))
+      if os.exists(root.path)
+      path <- (if (os.isDir(root.path)) os.walk(root.path) else Seq(root.path))
+      if os.isFile(path) && ((path.ext == "scala" || path.ext == "java") && !isHiddenFile(path))
     } yield PathRef(path)
   }
 
@@ -293,7 +291,7 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
     */
   def jar = T{
     createJar(
-      localClasspath().map(_.path).filter(exists),
+      localClasspath().map(_.path).filter(os.exists),
       mainClass()
     )
   }
@@ -306,13 +304,13 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
     val outDir = T.ctx().dest
 
     val javadocDir = outDir / 'javadoc
-    mkdir(javadocDir)
+    os.makeDir.all(javadocDir)
 
     val files = for{
       ref <- allSources()
-      if exists(ref.path)
-      p <- (if (ref.path.isDir) ls.rec(ref.path) else Seq(ref.path))
-      if p.isFile && (p.ext == "java")
+      if os.exists(ref.path)
+      p <- (if (os.isDir(ref.path)) os.walk(ref.path) else Seq(ref.path))
+      if os.isFile(p) && (p.ext == "java")
     } yield p.toNIO.toString
 
     val options = Seq("-d", javadocDir.toNIO.toString)
@@ -340,7 +338,7 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
     * The source jar, containing only source code for publishing to Maven Central
     */
   def sourceJar = T {
-    createJar((allSources() ++ resources()).map(_.path).filter(exists))
+    createJar((allSources() ++ resources()).map(_.path).filter(os.exists))
   }
 
   /**
@@ -409,12 +407,12 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
       forkEnv(),
       args,
       workingDir = forkWorkingDir()
-    )) catch { case e: InteractiveShelloutException =>
+    )) catch { case e: Exception =>
        Result.Failure("subprocess failed")
     }
   }
 
-  private[this] def backgroundSetup(dest: Path) = {
+  private[this] def backgroundSetup(dest: os.Path) = {
     val token = java.util.UUID.randomUUID().toString
     val procId = dest / ".mill-background-process-id"
     val procTombstone = dest / ".mill-background-process-tombstone"
@@ -432,9 +430,9 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
     // killed via some other means, and continue anyway.
     val start = System.currentTimeMillis()
     while({
-      if (exists(procTombstone)) {
+      if (os.exists(procTombstone)) {
         Thread.sleep(10)
-        rm(procTombstone)
+        os.remove.all(procTombstone)
         true
       } else {
         Thread.sleep(10)
@@ -442,8 +440,8 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
       }
     })()
 
-    write(procId, token)
-    write(procTombstone, token)
+    os.write(procId, token)
+    os.write(procTombstone, token)
     (procId, procTombstone, token)
   }
 
@@ -468,7 +466,7 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
       Seq(procId.toString, procTombstone.toString, token, finalMainClass()) ++ args,
       workingDir = forkWorkingDir(),
       background = true
-    )) catch { case e: InteractiveShelloutException =>
+    )) catch { case e: Exception =>
        Result.Failure("subprocess failed")
     }
   }
@@ -486,7 +484,7 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
       Seq(procId.toString, procTombstone.toString, token, mainClass) ++ args,
       workingDir = forkWorkingDir(),
       background = true
-    )) catch { case e: InteractiveShelloutException =>
+    )) catch { case e: Exception =>
       Result.Failure("subprocess failed")
     }
   }
@@ -513,7 +511,7 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
       forkEnv(),
       args,
       workingDir = forkWorkingDir()
-    )) catch { case e: InteractiveShelloutException =>
+    )) catch { case e: Exception =>
       Result.Failure("subprocess failed")
     }
   }
@@ -524,7 +522,7 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
 
   def artifactId: T[String] = artifactName()
 
-  def intellijModulePath: Path = millSourcePath
+  def intellijModulePath: os.Path = millSourcePath
 
   def forkWorkingDir = T{ ammonite.ops.pwd }
 
diff --git a/scalalib/src/mill/scalalib/Lib.scala b/scalalib/src/mill/scalalib/Lib.scala
index 17eeba3e..80723637 100644
--- a/scalalib/src/mill/scalalib/Lib.scala
+++ b/scalalib/src/mill/scalalib/Lib.scala
@@ -7,7 +7,6 @@ import java.lang.reflect.Modifier
 import java.util.zip.ZipInputStream
 import javax.tools.ToolProvider
 
-import ammonite.ops._
 import ammonite.util.Util
 import coursier.{Cache, Dependency, Fetch, Repository, Resolution}
 import Dep.isDotty
@@ -23,8 +22,8 @@ object CompilationResult {
   implicit val jsonFormatter: upickle.default.ReadWriter[CompilationResult] = upickle.default.macroRW
 }
 
-// analysisFile is represented by Path, so we won't break caches after file changes
-case class CompilationResult(analysisFile: Path, classes: PathRef)
+// analysisFile is represented by os.Path, so we won't break caches after file changes
+case class CompilationResult(analysisFile: os.Path, classes: PathRef)
 
 object Lib{
   private val ReleaseVersion = raw"""(\d+)\.(\d+)\.(\d+)""".r
@@ -40,7 +39,7 @@ object Lib{
     }
   }
 
-  def grepJar(classPath: Agg[Path], name: String, version: String, sources: Boolean = false) = {
+  def grepJar(classPath: Agg[os.Path], name: String, version: String, sources: Boolean = false) = {
     val suffix = if (sources) "-sources" else ""
     val mavenStylePath = s"$name-$version$suffix.jar"
     val ivyStylePath = {
@@ -111,22 +110,22 @@ object Lib{
     ivy"$scalaOrganization:scala-library:$scalaVersion".forceVersion()
   )
 
-  def listClassFiles(base: Path): Iterator[String] = {
-    if (base.isDir) ls.rec(base).toIterator.filter(_.ext == "class").map(_.relativeTo(base).toString)
+  def listClassFiles(base: os.Path): Iterator[String] = {
+    if (os.isDir(base)) os.walk(base).toIterator.filter(_.ext == "class").map(_.relativeTo(base).toString)
     else {
       val zip = new ZipInputStream(new FileInputStream(base.toIO))
       Iterator.continually(zip.getNextEntry).takeWhile(_ != null).map(_.getName).filter(_.endsWith(".class"))
     }
   }
 
-  def discoverTests(cl: ClassLoader, framework: Framework, classpath: Agg[Path]) = {
+  def discoverTests(cl: ClassLoader, framework: Framework, classpath: Agg[os.Path]) = {
 
     val fingerprints = framework.fingerprints()
 
     val testClasses = classpath.flatMap { base =>
       // Don't blow up if there are no classfiles representing
       // the tests to run Instead just don't run anything
-      if (!exists(base)) Nil
+      if (!os.exists(base)) Nil
       else listClassFiles(base).flatMap { path =>
         val cls = cl.loadClass(path.stripSuffix(".class").replace('/', '.'))
         val publicConstructorCount =
diff --git a/scalalib/src/mill/scalalib/MiscModule.scala b/scalalib/src/mill/scalalib/MiscModule.scala
index 02a6ebf9..c6449d6e 100644
--- a/scalalib/src/mill/scalalib/MiscModule.scala
+++ b/scalalib/src/mill/scalalib/MiscModule.scala
@@ -1,13 +1,12 @@
 package mill
 package scalalib
 
-import ammonite.ops.{Path, RelPath}
 import mill.define.Cross.Resolver
 import mill.define.{Cross, Task}
 import mill.eval.{PathRef, Result}
 import mill.util.Loose.Agg
 object CrossModuleBase{
-  def scalaVersionPaths(scalaVersion: String, f: String => Path) = {
+  def scalaVersionPaths(scalaVersion: String, f: String => os.Path) = {
     for(segments <- scalaVersion.split('.').inits.filter(_.nonEmpty))
     yield PathRef(f(segments.mkString(".")))
   }
diff --git a/scalalib/src/mill/scalalib/PublishModule.scala b/scalalib/src/mill/scalalib/PublishModule.scala
index 5c567452..a3d0856f 100644
--- a/scalalib/src/mill/scalalib/PublishModule.scala
+++ b/scalalib/src/mill/scalalib/PublishModule.scala
@@ -1,7 +1,6 @@
 package mill
 package scalalib
 
-import ammonite.ops._
 import mill.define.{ExternalModule, Task}
 import mill.eval.PathRef
 import mill.scalalib.publish.{Artifact, SonatypePublisher}
@@ -29,14 +28,14 @@ trait PublishModule extends JavaModule { outer =>
   def pom = T {
     val pom = Pom(artifactMetadata(), publishXmlDeps(), artifactId(), pomSettings())
     val pomPath = T.ctx().dest / s"${artifactId()}-${publishVersion()}.pom"
-    write.over(pomPath, pom)
+    os.write.over(pomPath, pom)
     PathRef(pomPath)
   }
 
   def ivy = T {
     val ivy = Ivy(artifactMetadata(), publishXmlDeps())
     val ivyPath = T.ctx().dest / "ivy.xml"
-    write.over(ivyPath, ivy)
+    os.write.over(ivyPath, ivy)
     PathRef(ivyPath)
   }
 
@@ -103,7 +102,7 @@ object PublishModule extends ExternalModule {
                  sonatypeSnapshotUri: String = "https://oss.sonatype.org/content/repositories/snapshots",
                  signed: Boolean = true) = T.command {
 
-    val x: Seq[(Seq[(Path, String)], Artifact)] = Task.sequence(publishArtifacts.value)().map{
+    val x: Seq[(Seq[(os.Path, String)], Artifact)] = Task.sequence(publishArtifacts.value)().map{
       case PublishModule.PublishData(a, s) => (s.map{case (p, f) => (p.path, f)}, a)
     }
     new SonatypePublisher(
diff --git a/scalalib/src/mill/scalalib/ScalaModule.scala b/scalalib/src/mill/scalalib/ScalaModule.scala
index 3c058013..80caf6a9 100644
--- a/scalalib/src/mill/scalalib/ScalaModule.scala
+++ b/scalalib/src/mill/scalalib/ScalaModule.scala
@@ -1,7 +1,6 @@
 package mill
 package scalalib
 
-import ammonite.ops._
 import coursier.Repository
 import mill.define.{Target, Task, TaskModule}
 import mill.eval.{PathRef, Result}
@@ -171,7 +170,7 @@ trait ScalaModule extends JavaModule { outer =>
     val outDir = T.ctx().dest
 
     val javadocDir = outDir / 'javadoc
-    mkdir(javadocDir)
+    os.makeDir.all(javadocDir)
 
     val files = allSourceFiles().map(_.path.toString)
 
@@ -215,7 +214,7 @@ trait ScalaModule extends JavaModule { outer =>
             "scala.tools.nsc.MainGenericRunner",
         classPath = runClasspath().map(_.path) ++ scalaCompilerClasspath().map(_.path),
         mainArgs = Seq("-usejavacp"),
-        workingDir = pwd
+        workingDir = os.pwd
       )
       Result.Success()
     }
@@ -246,7 +245,7 @@ trait ScalaModule extends JavaModule { outer =>
         mainClass = "ammonite.Main",
         classPath = ammoniteReplClasspath().map(_.path),
         mainArgs = replOptions,
-        workingDir = pwd
+        workingDir = os.pwd
       )
       Result.Success()
     }
diff --git a/scalalib/src/mill/scalalib/TestRunner.scala b/scalalib/src/mill/scalalib/TestRunner.scala
index 0b9c897f..42e65d63 100644
--- a/scalalib/src/mill/scalalib/TestRunner.scala
+++ b/scalalib/src/mill/scalalib/TestRunner.scala
@@ -1,5 +1,4 @@
 package mill.scalalib
-import ammonite.ops.Path
 import ammonite.util.Colors
 import mill.Agg
 import mill.modules.Jvm
@@ -40,12 +39,12 @@ object TestRunner {
           System.in,
           debugEnabled = false
         )
-        val home = Path(homeStr)
+        val home = os.Path(homeStr)
       }
       val result = runTests(
         frameworkInstances = TestRunner.frameworks(frameworks),
-        entireClasspath = Agg.from(classpath.map(Path(_))),
-        testClassfilePath = Agg(Path(testCp)),
+        entireClasspath = Agg.from(classpath.map(os.Path(_))),
+        testClassfilePath = Agg(os.Path(testCp)),
         args = arguments
       )(ctx)
 
@@ -53,7 +52,7 @@ object TestRunner {
       // dirtied the thread-interrupted flag and forgot to clean up. Otherwise
       // that flag causes writing the results to disk to fail
       Thread.interrupted()
-      ammonite.ops.write(Path(outputPath), upickle.default.write(result))
+      ammonite.ops.write(os.Path(outputPath), upickle.default.write(result))
     }catch{case e: Throwable =>
       println(e)
       e.printStackTrace()
@@ -65,8 +64,8 @@ object TestRunner {
   }
 
   def runTests(frameworkInstances: ClassLoader => Seq[sbt.testing.Framework],
-               entireClasspath: Agg[Path],
-               testClassfilePath: Agg[Path],
+               entireClasspath: Agg[os.Path],
+               testClassfilePath: Agg[os.Path],
                args: Seq[String])
               (implicit ctx: Ctx.Log with Ctx.Home): (String, Seq[mill.scalalib.TestRunner.Result]) = {
     //Leave the context class loader set and open so that shutdown hooks can access it
diff --git a/scalalib/src/mill/scalalib/ZincWorkerApi.scala b/scalalib/src/mill/scalalib/ZincWorkerApi.scala
index 8e95eb29..dbcaa6da 100644
--- a/scalalib/src/mill/scalalib/ZincWorkerApi.scala
+++ b/scalalib/src/mill/scalalib/ZincWorkerApi.scala
@@ -1,7 +1,5 @@
 package mill.scalalib
 
-
-import ammonite.ops.Path
 import coursier.Cache
 import coursier.maven.MavenRepository
 import mill.Agg
@@ -60,30 +58,30 @@ trait ZincWorkerModule extends mill.Module{
 trait ZincWorkerApi {
   /** Compile a Java-only project */
   def compileJava(upstreamCompileOutput: Seq[CompilationResult],
-                  sources: Agg[Path],
-                  compileClasspath: Agg[Path],
+                  sources: Agg[os.Path],
+                  compileClasspath: Agg[os.Path],
                   javacOptions: Seq[String])
                  (implicit ctx: mill.util.Ctx): mill.eval.Result[CompilationResult]
 
   /** Compile a mixed Scala/Java or Scala-only project */
   def compileMixed(upstreamCompileOutput: Seq[CompilationResult],
-                   sources: Agg[Path],
-                   compileClasspath: Agg[Path],
+                   sources: Agg[os.Path],
+                   compileClasspath: Agg[os.Path],
                    javacOptions: Seq[String],
                    scalaVersion: String,
                    scalacOptions: Seq[String],
-                   compilerBridgeSources: Path,
-                   compilerClasspath: Agg[Path],
-                   scalacPluginClasspath: Agg[Path])
+                   compilerBridgeSources: os.Path,
+                   compilerClasspath: Agg[os.Path],
+                   scalacPluginClasspath: Agg[os.Path])
                   (implicit ctx: mill.util.Ctx): mill.eval.Result[CompilationResult]
 
   def discoverMainClasses(compilationResult: CompilationResult)
                          (implicit ctx: mill.util.Ctx): Seq[String]
 
   def docJar(scalaVersion: String,
-             compilerBridgeSources: Path,
-             compilerClasspath: Agg[Path],
-             scalacPluginClasspath: Agg[Path],
+             compilerBridgeSources: os.Path,
+             compilerClasspath: Agg[os.Path],
+             scalacPluginClasspath: Agg[os.Path],
              args: Seq[String])
             (implicit ctx: mill.util.Ctx): Boolean
 }
diff --git a/scalalib/src/mill/scalalib/dependency/versions/VersionsFinder.scala b/scalalib/src/mill/scalalib/dependency/versions/VersionsFinder.scala
index abe6e012..b1033688 100644
--- a/scalalib/src/mill/scalalib/dependency/versions/VersionsFinder.scala
+++ b/scalalib/src/mill/scalalib/dependency/versions/VersionsFinder.scala
@@ -1,6 +1,5 @@
 package mill.scalalib.dependency.versions
 
-import ammonite.ops.pwd
 import mill.define.{BaseModule, Task}
 import mill.eval.Evaluator
 import mill.scalalib.dependency.metadata.MetadataLoaderFactory
@@ -13,7 +12,7 @@ private[dependency] object VersionsFinder {
   def findVersions(ctx: Log with Home,
                    rootModule: BaseModule): Seq[ModuleDependenciesVersions] = {
     val evaluator =
-      new Evaluator(ctx.home, pwd / 'out, pwd / 'out, rootModule, ctx.log)
+      new Evaluator(ctx.home, os.pwd / 'out, os.pwd / 'out, rootModule, ctx.log)
 
     val javaModules = rootModule.millInternal.modules.collect {
       case javaModule: JavaModule => javaModule
diff --git a/scalalib/src/mill/scalalib/publish/LocalPublisher.scala b/scalalib/src/mill/scalalib/publish/LocalPublisher.scala
index a8a703fc..d9839831 100644
--- a/scalalib/src/mill/scalalib/publish/LocalPublisher.scala
+++ b/scalalib/src/mill/scalalib/publish/LocalPublisher.scala
@@ -1,16 +1,15 @@
 package mill.scalalib.publish
 
-import ammonite.ops._
 
 object LocalPublisher {
 
-  private val root: Path = home / ".ivy2" / "local"
+  private val root: os.Path = os.home / ".ivy2" / "local"
 
-  def publish(jar: Path,
-              sourcesJar: Path,
-              docJar: Path,
-              pom: Path,
-              ivy: Path,
+  def publish(jar: os.Path,
+              sourcesJar: os.Path,
+              docJar: os.Path,
+              pom: os.Path,
+              ivy: os.Path,
               artifact: Artifact): Unit = {
     val releaseDir = root / artifact.group / artifact.id / artifact.version
     writeFiles(
@@ -22,11 +21,11 @@ object LocalPublisher {
     )
   }
 
-  private def writeFiles(fromTo: (Path, Path)*): Unit = {
+  private def writeFiles(fromTo: (os.Path, os.Path)*): Unit = {
     fromTo.foreach {
       case (from, to) =>
-        mkdir(to / up)
-        cp.over(from, to)
+        os.makeDir.all(to / os.up)
+        os.copy.over(from, to)
     }
   }
 
diff --git a/scalalib/src/mill/scalalib/publish/SonatypePublisher.scala b/scalalib/src/mill/scalalib/publish/SonatypePublisher.scala
index 47ec8dbf..5e596618 100644
--- a/scalalib/src/mill/scalalib/publish/SonatypePublisher.scala
+++ b/scalalib/src/mill/scalalib/publish/SonatypePublisher.scala
@@ -3,7 +3,6 @@ package mill.scalalib.publish
 import java.math.BigInteger
 import java.security.MessageDigest
 
-import ammonite.ops._
 import mill.util.Logger
 
 import scalaj.http.HttpResponse
@@ -17,10 +16,10 @@ class SonatypePublisher(uri: String,
 
   private val api = new SonatypeHttpApi(uri, credentials)
 
-  def publish(fileMapping: Seq[(Path, String)], artifact: Artifact, release: Boolean): Unit = {
+  def publish(fileMapping: Seq[(os.Path, String)], artifact: Artifact, release: Boolean): Unit = {
     publishAll(release, fileMapping -> artifact)
   }
-  def publishAll(release: Boolean, artifacts: (Seq[(Path, String)], Artifact)*): Unit = {
+  def publishAll(release: Boolean, artifacts: (Seq[(os.Path, String)], Artifact)*): Unit = {
 
     val mappings = for ((fileMapping0, artifact) <- artifacts) yield {
       val publishPath = Seq(
@@ -36,7 +35,7 @@ class SonatypePublisher(uri: String,
 
       artifact -> (fileMapping ++ signedArtifacts).flatMap {
         case (file, name) =>
-          val content = read.bytes(file)
+          val content = os.read.bytes(file)
 
           Seq(
             name -> content,
@@ -136,16 +135,17 @@ class SonatypePublisher(uri: String,
   }
 
   // http://central.sonatype.org/pages/working-with-pgp-signatures.html#signing-a-file
-  private def poorMansSign(file: Path, maybePassphrase: Option[String]): Path = {
+  private def poorMansSign(file: os.Path, maybePassphrase: Option[String]): os.Path = {
     val fileName = file.toString
-    import ammonite.ops.ImplicitWd._
     maybePassphrase match {
       case Some(passphrase) =>
-        %("gpg", "--passphrase", passphrase, "--batch", "--yes", "-a", "-b", fileName)
+        os.proc("gpg", "--passphrase", passphrase, "--batch", "--yes", "-a", "-b", fileName)
+          .call(stdin = os.Inherit, stdout = os.Inherit, stderr = os.Inherit)
       case None =>
-        %("gpg", "--batch", "--yes", "-a", "-b", fileName)
+        os.proc("gpg", "--batch", "--yes", "-a", "-b", fileName)
+          .call(stdin = os.Inherit, stdout = os.Inherit, stderr = os.Inherit)
     }
-    Path(fileName + ".asc")
+    os.Path(fileName + ".asc")
   }
 
   private def md5hex(bytes: Array[Byte]): Array[Byte] =
diff --git a/scalalib/src/mill/scalalib/scalafmt/ScalafmtModule.scala b/scalalib/src/mill/scalalib/scalafmt/ScalafmtModule.scala
index 74f64e28..6a81d975 100644
--- a/scalalib/src/mill/scalalib/scalafmt/ScalafmtModule.scala
+++ b/scalalib/src/mill/scalalib/scalafmt/ScalafmtModule.scala
@@ -1,6 +1,5 @@
 package mill.scalalib.scalafmt
 
-import ammonite.ops.{exists, ls, pwd}
 import mill._
 import mill.define._
 import mill.scalalib._
@@ -19,7 +18,7 @@ trait ScalafmtModule extends JavaModule {
 
   def scalafmtVersion: T[String] = "1.5.1"
 
-  def scalafmtConfig: Sources = T.sources(pwd / ".scalafmt.conf")
+  def scalafmtConfig: Sources = T.sources(os.pwd / ".scalafmt.conf")
 
   def scalafmtDeps: T[Agg[PathRef]] = T {
     Lib.resolveDependencies(
@@ -31,8 +30,8 @@ trait ScalafmtModule extends JavaModule {
 
   protected def filesToFormat(sources: Seq[PathRef]) = {
     for {
-      pathRef <- sources if exists(pathRef.path)
-      file <- ls.rec(pathRef.path) if file.isFile && file.ext == "scala"
+      pathRef <- sources if os.exists(pathRef.path)
+      file <- os.walk(pathRef.path) if os.isFile(file) && file.ext == "scala"
     } yield PathRef(file)
   }
 
diff --git a/scalalib/src/mill/scalalib/scalafmt/ScalafmtWorker.scala b/scalalib/src/mill/scalalib/scalafmt/ScalafmtWorker.scala
index d9921e9d..41fad45b 100644
--- a/scalalib/src/mill/scalalib/scalafmt/ScalafmtWorker.scala
+++ b/scalalib/src/mill/scalalib/scalafmt/ScalafmtWorker.scala
@@ -1,6 +1,5 @@
 package mill.scalalib.scalafmt
 
-import ammonite.ops.{Path, exists}
 import mill._
 import mill.define.{Discover, ExternalModule, Worker}
 import mill.modules.Jvm
@@ -15,12 +14,12 @@ object ScalafmtWorkerModule extends ExternalModule {
 }
 
 private[scalafmt] class ScalafmtWorker {
-  private val reformatted: mutable.Map[Path, Int] = mutable.Map.empty
+  private val reformatted: mutable.Map[os.Path, Int] = mutable.Map.empty
   private var configSig: Int = 0
 
   def reformat(input: Seq[PathRef],
                scalafmtConfig: PathRef,
-               scalafmtClasspath: Agg[Path])(implicit ctx: Ctx): Unit = {
+               scalafmtClasspath: Agg[os.Path])(implicit ctx: Ctx): Unit = {
     val toFormat =
       if (scalafmtConfig.sig != configSig) input
       else
@@ -43,11 +42,11 @@ private[scalafmt] class ScalafmtWorker {
 
   private val cliFlags = Seq("--non-interactive", "--quiet")
 
-  private def reformatAction(toFormat: Seq[Path],
-                             config: Path,
-                             classpath: Agg[Path])(implicit ctx: Ctx) = {
+  private def reformatAction(toFormat: Seq[os.Path],
+                             config: os.Path,
+                             classpath: Agg[os.Path])(implicit ctx: Ctx) = {
     val configFlags =
-      if (exists(config)) Seq("--config", config.toString) else Seq.empty
+      if (os.exists(config)) Seq("--config", config.toString) else Seq.empty
     Jvm.subprocess(
       "org.scalafmt.cli.Cli",
       classpath,
diff --git a/scalalib/test/src/mill/scalalib/GenIdeaTests.scala b/scalalib/test/src/mill/scalalib/GenIdeaTests.scala
index db70a325..d4a8cabd 100644
--- a/scalalib/test/src/mill/scalalib/GenIdeaTests.scala
+++ b/scalalib/test/src/mill/scalalib/GenIdeaTests.scala
@@ -1,6 +1,5 @@
 package mill.scalalib
 
-import ammonite.ops._
 import coursier.Cache
 import mill._
 import mill.util.{TestEvaluator, TestUtil}
@@ -8,7 +7,7 @@ import utest._
 
 object GenIdeaTests extends TestSuite {
 
-  val millSourcePath = pwd / 'target / 'workspace / "gen-idea"
+  val millSourcePath = os.pwd / 'target / 'workspace / "gen-idea"
 
   trait HelloWorldModule extends scalalib.ScalaModule {
     def scalaVersion = "2.12.4"
@@ -31,7 +30,7 @@ object GenIdeaTests extends TestSuite {
         HelloWorld,
         ("JDK_1_8", "1.8 (1)"), fetchMillModules = false)
       for((relPath, xml) <- layout){
-        write.over(millSourcePath/ "generated"/ relPath, pp.format(xml))
+        os.write.over(millSourcePath/ "generated"/ relPath, pp.format(xml))
       }
 
       Seq(
@@ -49,7 +48,7 @@ object GenIdeaTests extends TestSuite {
           millSourcePath / "generated" / ".idea" / "misc.xml"
       ).foreach { case (resource, generated) =>
           val resourceString = scala.io.Source.fromResource(resource).getLines().mkString("\n")
-          val generatedString = normaliseLibraryPaths(read! generated)
+          val generatedString = normaliseLibraryPaths(os.read(generated))
 
           assert(resourceString == generatedString)
         }
diff --git a/scalalib/test/src/mill/scalalib/HelloJavaTests.scala b/scalalib/test/src/mill/scalalib/HelloJavaTests.scala
index 7e044475..ff0de5a6 100644
--- a/scalalib/test/src/mill/scalalib/HelloJavaTests.scala
+++ b/scalalib/test/src/mill/scalalib/HelloJavaTests.scala
@@ -2,8 +2,6 @@ package mill
 package scalalib
 
 
-import ammonite.ops.{%, %%, cp, ls, mkdir, pwd, rm, up}
-import ammonite.ops.ImplicitWd._
 import mill.eval.Result
 import mill.util.{TestEvaluator, TestUtil}
 import utest._
@@ -27,14 +25,14 @@ object HelloJavaTests extends TestSuite {
       object test extends Tests with JUnitTests
     }
   }
-  val resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-java"
+  val resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-java"
 
   def init()(implicit tp: TestPath) = {
     val eval = new TestEvaluator(HelloJava)
-    rm(HelloJava.millSourcePath)
-    rm(eval.outPath)
-    mkdir(HelloJava.millSourcePath / up)
-    cp(resourcePath, HelloJava.millSourcePath)
+    os.remove.all(HelloJava.millSourcePath)
+    os.remove.all(eval.outPath)
+    os.makeDir.all(HelloJava.millSourcePath / os.up)
+    os.copy(resourcePath, HelloJava.millSourcePath)
     eval
   }
   def tests: Tests = Tests {
@@ -49,10 +47,10 @@ object HelloJavaTests extends TestSuite {
         res1 == res2,
         n1 != 0,
         n2 != 0,
-        ls.rec(res1.classes.path).exists(_.last == "Core.class"),
-        !ls.rec(res1.classes.path).exists(_.last == "Main.class"),
-        ls.rec(res3.classes.path).exists(_.last == "Main.class"),
-        !ls.rec(res3.classes.path).exists(_.last == "Core.class")
+        os.walk(res1.classes.path).exists(_.last == "Core.class"),
+        !os.walk(res1.classes.path).exists(_.last == "Main.class"),
+        os.walk(res3.classes.path).exists(_.last == "Main.class"),
+        !os.walk(res3.classes.path).exists(_.last == "Core.class")
       )
     }
     'docJar  - {
@@ -62,8 +60,8 @@ object HelloJavaTests extends TestSuite {
       val Right((ref2, _)) = eval.apply(HelloJava.app.docJar)
 
       assert(
-        %%("jar", "tf", ref1.path).out.lines.contains("hello/Core.html"),
-        %%("jar", "tf", ref2.path).out.lines.contains("hello/Main.html")
+        os.proc("jar", "tf", ref1.path).call().out.lines.contains("hello/Core.html"),
+        os.proc("jar", "tf", ref2.path).call().out.lines.contains("hello/Main.html")
       )
     }
     'test - {
diff --git a/scalalib/test/src/mill/scalalib/HelloWorldTests.scala b/scalalib/test/src/mill/scalalib/HelloWorldTests.scala
index 1839e275..67c4b433 100644
--- a/scalalib/test/src/mill/scalalib/HelloWorldTests.scala
+++ b/scalalib/test/src/mill/scalalib/HelloWorldTests.scala
@@ -1,8 +1,8 @@
 package mill.scalalib
 
+import java.io.ByteArrayOutputStream
 import java.util.jar.JarFile
 
-import ammonite.ops._
 import mill._
 import mill.define.Target
 import mill.eval.Result.Exception
@@ -265,7 +265,7 @@ object HelloWorldTests extends TestSuite {
      }
   }
 
-  val resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world"
+  val resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world"
 
   def jarMainClass(jar: JarFile): Option[String] = {
     import java.util.jar.Attributes._
@@ -279,10 +279,12 @@ object HelloWorldTests extends TestSuite {
 
   def readFileFromJar(jar: JarFile, name: String): String = {
     val is = jar.getInputStream(jar.getEntry(name))
-    read(is)
+    val baos = new ByteArrayOutputStream()
+    os.Internals.transfer(is, baos)
+    new String(baos.toByteArray)
   }
 
-  def compileClassfiles = Seq[RelPath](
+  def compileClassfiles = Seq[os.RelPath](
     "Main.class",
     "Main$.class",
     "Main0.class",
@@ -292,14 +294,14 @@ object HelloWorldTests extends TestSuite {
     "Person$.class"
   )
 
-  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: Path = resourcePath)
+  def workspaceTest[T](m: TestUtil.BaseModule, resourcePath: os.Path = resourcePath)
                       (t: TestEvaluator => T)
                       (implicit tp: TestPath): T = {
     val eval = new TestEvaluator(m)
-    rm(m.millSourcePath)
-    rm(eval.outPath)
-    mkdir(m.millSourcePath / up)
-    cp(resourcePath, m.millSourcePath)
+    os.remove.all(m.millSourcePath)
+    os.remove.all(eval.outPath)
+    os.makeDir.all(m.millSourcePath / os.up)
+    os.copy(resourcePath, m.millSourcePath)
     t(eval)
   }
 
@@ -371,29 +373,29 @@ object HelloWorldTests extends TestSuite {
       // make sure options are passed during ScalaDoc generation
       'docJarWithTitle - workspaceTest(
         HelloWorldDocTitle,
-        resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world"
+        resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world"
       ){ eval =>
         val Right((_, evalCount)) = eval.apply(HelloWorldDocTitle.core.docJar)
         assert(
           evalCount > 0,
-          read(eval.outPath / 'core / 'docJar / 'dest / 'javadoc / "index.html").contains("<span id=\"doc-title\">Hello World")
+          os.read(eval.outPath / 'core / 'docJar / 'dest / 'javadoc / "index.html").contains("<span id=\"doc-title\">Hello World")
         )
       }
       'docJarWithVersion - workspaceTest(
         HelloWorldWithDocVersion,
-        resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world"
+        resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world"
       ){ eval =>
         // scaladoc generation fails because of "-Xfatal-warnings" flag
         val Left(Result.Failure("docJar generation failed", None)) = eval.apply(HelloWorldWithDocVersion.core.docJar)
       }
       'docJarOnlyVersion - workspaceTest(
         HelloWorldOnlyDocVersion,
-        resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world"
+        resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world"
       ){ eval =>
         val Right((_, evalCount)) = eval.apply(HelloWorldOnlyDocVersion.core.docJar)
         assert(
           evalCount > 0,
-          read(eval.outPath / 'core / 'docJar / 'dest / 'javadoc / "index.html").contains("<span id=\"doc-version\">1.2.3")
+          os.read(eval.outPath / 'core / 'docJar / 'dest / 'javadoc / "index.html").contains("<span id=\"doc-version\">1.2.3")
         )
       }
     }
@@ -426,13 +428,13 @@ object HelloWorldTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(HelloWorld.core.compile)
 
         val analysisFile = result.analysisFile
-        val outputFiles = ls.rec(result.classes.path)
+        val outputFiles = os.walk(result.classes.path)
         val expectedClassfiles = compileClassfiles.map(
           eval.outPath / 'core / 'compile / 'dest / 'classes / _
         )
         assert(
           result.classes.path == eval.outPath / 'core / 'compile / 'dest / 'classes,
-          exists(analysisFile),
+          os.exists(analysisFile),
           outputFiles.nonEmpty,
           outputFiles.forall(expectedClassfiles.contains),
           evalCount > 0
@@ -447,13 +449,13 @@ object HelloWorldTests extends TestSuite {
         val Right((_, freshCount)) = eval.apply(HelloWorld.core.compile)
         assert(freshCount > 0)
 
-        write.append(HelloWorld.millSourcePath / 'core / 'src / "Main.scala", "\n")
+        os.write.append(HelloWorld.millSourcePath / 'core / 'src / "Main.scala", "\n")
 
         val Right((_, incCompileCount)) = eval.apply(HelloWorld.core.compile)
         assert(incCompileCount > 0, incCompileCount < freshCount)
       }
       'failOnError - workspaceTest(HelloWorld){eval =>
-        write.append(HelloWorld.millSourcePath / 'core / 'src / "Main.scala", "val x: ")
+        os.write.append(HelloWorld.millSourcePath / 'core / 'src / "Main.scala", "val x: ")
 
         val Left(Result.Failure("Compilation failed", _)) = eval.apply(HelloWorld.core.compile)
 
@@ -464,13 +466,13 @@ object HelloWorldTests extends TestSuite {
         )
 
         assert(
-          ls.rec(paths.dest / 'classes).isEmpty,
-          !exists(paths.meta)
+          os.walk(paths.dest / 'classes).isEmpty,
+          !os.exists(paths.meta)
         )
         // Works when fixed
-        write.over(
+        os.write.over(
           HelloWorld.millSourcePath / 'core / 'src / "Main.scala",
-          read(HelloWorld.millSourcePath / 'core / 'src / "Main.scala").dropRight("val x: ".length)
+          os.read(HelloWorld.millSourcePath / 'core / 'src / "Main.scala").dropRight("val x: ".length)
         )
 
         val Right((result, evalCount)) = eval.apply(HelloWorld.core.compile)
@@ -489,8 +491,8 @@ object HelloWorldTests extends TestSuite {
         assert(evalCount > 0)
 
         assert(
-          exists(runResult),
-          read(runResult) == "hello rockjam, your age is: 25"
+          os.exists(runResult),
+          os.read(runResult) == "hello rockjam, your age is: 25"
         )
       }
       'runCross - {
@@ -506,8 +508,8 @@ object HelloWorldTests extends TestSuite {
 
 
           assert(
-            exists(runResult),
-            read(runResult) == expectedOut
+            os.exists(runResult),
+            os.read(runResult) == expectedOut
           )
         }
         'v210 - TestUtil.disableInJava9OrAbove(workspaceTest(CrossHelloWorld)(cross(_, "2.10.6", "2.10.6 rox")))
@@ -522,7 +524,7 @@ object HelloWorldTests extends TestSuite {
         val Left(Result.Failure("subprocess failed", _)) = eval.apply(HelloWorld.core.runMain("Invalid"))
       }
       'notRunWhenCompileFailed - workspaceTest(HelloWorld){eval =>
-        write.append(HelloWorld.millSourcePath / 'core / 'src / "Main.scala", "val x: ")
+        os.write.append(HelloWorld.millSourcePath / 'core / 'src / "Main.scala", "val x: ")
 
         val Left(Result.Failure("Compilation failed", _)) = eval.apply(HelloWorld.core.runMain("Main"))
 
@@ -540,13 +542,13 @@ object HelloWorldTests extends TestSuite {
 
 
         assert(
-          exists(runResult),
-          read(runResult) == "hello rockjam, your age is: 25"
+          os.exists(runResult),
+          os.read(runResult) == "hello rockjam, your age is: 25"
         )
       }
       'notRunWithoutMainClass - workspaceTest(
         HelloWorldWithoutMain,
-        pwd / 'scalalib / 'test / 'resources / "hello-world-no-main"
+        os.pwd / 'scalalib / 'test / 'resources / "hello-world-no-main"
       ){eval =>
         val Left(Result.Failure(_, None)) = eval.apply(HelloWorldWithoutMain.core.run())
       }
@@ -563,8 +565,8 @@ object HelloWorldTests extends TestSuite {
 
 
         assert(
-          exists(runResult),
-          read(runResult) == "hello rockjam, your age is: 25"
+          os.exists(runResult),
+          os.read(runResult) == "hello rockjam, your age is: 25"
         )
       }
     }
@@ -580,8 +582,8 @@ object HelloWorldTests extends TestSuite {
 
 
         assert(
-          exists(runResult),
-          read(runResult) == "hello rockjam, your age is: 25"
+          os.exists(runResult),
+          os.read(runResult) == "hello rockjam, your age is: 25"
         )
       }
       'runWithDefaultMain - workspaceTest(HelloWorldDefaultMain){eval =>
@@ -594,13 +596,13 @@ object HelloWorldTests extends TestSuite {
 
 
         assert(
-          exists(runResult),
-          read(runResult) == "hello rockjam, your age is: 25"
+          os.exists(runResult),
+          os.read(runResult) == "hello rockjam, your age is: 25"
         )
       }
       'notRunWithoutMainClass - workspaceTest(
         HelloWorldWithoutMain,
-        pwd / 'scalalib / 'test / 'resources / "hello-world-no-main"
+        os.pwd / 'scalalib / 'test / 'resources / "hello-world-no-main"
       ){eval =>
         val Left(Result.Failure(_, None)) = eval.apply(HelloWorldWithoutMain.core.runLocal())
 
@@ -612,15 +614,15 @@ object HelloWorldTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(HelloWorldWithMain.core.jar)
 
         assert(
-          exists(result.path),
+          os.exists(result.path),
           evalCount > 0
         )
 
         val jarFile = new JarFile(result.path.toIO)
         val entries = jarFile.entries().asScala.map(_.getName).toSet
 
-        val otherFiles = Seq[RelPath](
-          "META-INF" / "MANIFEST.MF",
+        val otherFiles = Seq[os.RelPath](
+          os.rel / "META-INF" / "MANIFEST.MF",
           "reference.conf"
         )
         val expectedFiles = compileClassfiles ++ otherFiles
@@ -639,7 +641,7 @@ object HelloWorldTests extends TestSuite {
         eval.apply(HelloWorld.core.compile)
 
         val logFile = outPath / 'core / 'compile / 'log
-        assert(exists(logFile))
+        assert(os.exists(logFile))
       }
     }
 
@@ -647,7 +649,7 @@ object HelloWorldTests extends TestSuite {
       'assembly - workspaceTest(HelloWorldWithMain){ eval =>
         val Right((result, evalCount)) = eval.apply(HelloWorldWithMain.core.assembly)
         assert(
-          exists(result.path),
+          os.exists(result.path),
           evalCount > 0
         )
         val jarFile = new JarFile(result.path.toIO)
@@ -687,7 +689,7 @@ object HelloWorldTests extends TestSuite {
             )
           }
 
-        val helloWorldMultiResourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world-multi"
+        val helloWorldMultiResourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world-multi"
 
         def checkAppendMulti[M <: TestUtil.BaseModule](
             module: M,
@@ -734,7 +736,7 @@ object HelloWorldTests extends TestSuite {
 
         def checkExclude[M <: TestUtil.BaseModule](module: M,
                                                    target: Target[PathRef],
-                                                   resourcePath: Path = resourcePath
+                                                   resourcePath: os.Path = resourcePath
                                                   ) =
           workspaceTest(module, resourcePath) { eval =>
             val Right((result, _)) = eval.apply(target)
@@ -814,16 +816,16 @@ object HelloWorldTests extends TestSuite {
         val Right((result, evalCount)) = eval.apply(HelloWorldWithMain.core.assembly)
 
         assert(
-          exists(result.path),
+          os.exists(result.path),
           evalCount > 0
         )
         val runResult = eval.outPath / "hello-mill"
 
-        %%("java", "-jar", result.path, runResult)(wd = eval.outPath)
+        os.proc("java", "-jar", result.path, runResult).call(cwd = eval.outPath)
 
         assert(
-          exists(runResult),
-          read(runResult) == "hello rockjam, your age is: 25"
+          os.exists(runResult),
+          os.read(runResult) == "hello rockjam, your age is: 25"
         )
       }
     }
@@ -866,7 +868,7 @@ object HelloWorldTests extends TestSuite {
       // make sure macros are applied when compiling/running
       'runMain - workspaceTest(
         HelloWorldMacros,
-        resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world-macros"
+        resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world-macros"
       ){ eval =>
         val Right((_, evalCount)) = eval.apply(HelloWorldMacros.core.runMain("Main"))
         assert(evalCount > 0)
@@ -874,7 +876,7 @@ object HelloWorldTests extends TestSuite {
       // make sure macros are applied when compiling during scaladoc generation
       'docJar - workspaceTest(
         HelloWorldMacros,
-        resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world-macros"
+        resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world-macros"
       ){ eval =>
         val Right((_, evalCount)) = eval.apply(HelloWorldMacros.core.docJar)
         assert(evalCount > 0)
@@ -885,7 +887,7 @@ object HelloWorldTests extends TestSuite {
       // make sure flags are passed when compiling/running
       'runMain - workspaceTest(
         HelloWorldFlags,
-        resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world-flags"
+        resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world-flags"
       ){ eval =>
         val Right((_, evalCount)) = eval.apply(HelloWorldFlags.core.runMain("Main"))
         assert(evalCount > 0)
@@ -893,7 +895,7 @@ object HelloWorldTests extends TestSuite {
       // make sure flags are passed during ScalaDoc generation
       'docJar - workspaceTest(
         HelloWorldFlags,
-        resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-world-flags"
+        resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-world-flags"
       ){ eval =>
         val Right((_, evalCount)) = eval.apply(HelloWorldFlags.core.docJar)
         assert(evalCount > 0)
@@ -902,7 +904,7 @@ object HelloWorldTests extends TestSuite {
 
     'scalacheck - workspaceTest(
       HelloScalacheck,
-      resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-scalacheck"
+      resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-scalacheck"
     ){ eval =>
       val Right((res, evalCount)) = eval.apply(HelloScalacheck.foo.test.test())
       assert(
@@ -918,7 +920,7 @@ object HelloWorldTests extends TestSuite {
 
     'dotty - workspaceTest(
       HelloDotty,
-      resourcePath = pwd / 'scalalib / 'test / 'resources / "hello-dotty"
+      resourcePath = os.pwd / 'scalalib / 'test / 'resources / "hello-dotty"
     ){ eval =>
       if (isJavaAtLeast("9")) {
         // Skip the test because Dotty does not support Java >= 9 yet
diff --git a/scalalib/test/src/mill/scalalib/scalafmt/ScalafmtTests.scala b/scalalib/test/src/mill/scalalib/scalafmt/ScalafmtTests.scala
index 89d549ff..dcbdb769 100644
--- a/scalalib/test/src/mill/scalalib/scalafmt/ScalafmtTests.scala
+++ b/scalalib/test/src/mill/scalalib/scalafmt/ScalafmtTests.scala
@@ -1,6 +1,5 @@
 package mill.scalalib.scalafmt
 
-import ammonite.ops._
 import mill.main.Tasks
 import mill.scalalib.ScalaModule
 import mill.util.{TestEvaluator, TestUtil}
@@ -20,17 +19,17 @@ object ScalafmtTests extends TestSuite {
     }
   }
 
-  val resourcePath = pwd / 'scalalib / 'test / 'resources / 'scalafmt
+  val resourcePath = os.pwd / 'scalalib / 'test / 'resources / 'scalafmt
 
   def workspaceTest[T](
       m: TestUtil.BaseModule,
-      resourcePath: Path = resourcePath)(t: TestEvaluator => T)(
+      resourcePath: os.Path = resourcePath)(t: TestEvaluator => T)(
       implicit tp: TestPath): T = {
     val eval = new TestEvaluator(m)
-    rm(m.millSourcePath)
-    rm(eval.outPath)
-    mkdir(m.millSourcePath / up)
-    cp(resourcePath, m.millSourcePath)
+    os.remove.all(m.millSourcePath)
+    os.remove.all(eval.outPath)
+    os.makeDir.all(m.millSourcePath / os.up)
+    os.copy(resourcePath, m.millSourcePath)
     t(eval)
   }
 
@@ -68,7 +67,7 @@ object ScalafmtTests extends TestSuite {
           )
 
           // reformat after change
-          write.over(cached("Main.scala").path,
+          os.write.over(cached("Main.scala").path,
                      cached("Main.scala").content + "\n object Foo")
 
           val Right(_) = eval.apply(reformatCommand)
@@ -89,16 +88,16 @@ object ScalafmtTests extends TestSuite {
     }
   }
 
-  case class FileInfo(content: String, modifyTime: Long, path: Path)
+  case class FileInfo(content: String, modifyTime: Long, path: os.Path)
 
   def getProjectFiles(m: ScalaModule, eval: TestEvaluator) = {
     val Right((sources, _)) = eval.apply(m.sources)
     val Right((resources, _)) = eval.apply(m.resources)
 
-    val sourcesFiles = sources.flatMap(p => ls.rec(p.path))
-    val resourcesFiles = resources.flatMap(p => ls.rec(p.path))
+    val sourcesFiles = sources.flatMap(p => os.walk(p.path))
+    val resourcesFiles = resources.flatMap(p => os.walk(p.path))
     (sourcesFiles ++ resourcesFiles).map { p =>
-      p.name -> FileInfo(read(p), p.mtime.toMillis, p)
+      p.last -> FileInfo(os.read(p), os.mtime(p), p)
     }.toMap
   }
 
diff --git a/scalalib/worker/src/mill/scalalib/worker/ZincWorkerImpl.scala b/scalalib/worker/src/mill/scalalib/worker/ZincWorkerImpl.scala
index 78595b14..d494760e 100644
--- a/scalalib/worker/src/mill/scalalib/worker/ZincWorkerImpl.scala
+++ b/scalalib/worker/src/mill/scalalib/worker/ZincWorkerImpl.scala
@@ -3,7 +3,6 @@ package mill.scalalib.worker
 import java.io.File
 import java.util.Optional
 
-import ammonite.ops.{Path, exists, ls, mkdir}
 import ammonite.util.Colors
 import mill.Agg
 import mill.eval.PathRef
@@ -50,9 +49,9 @@ class ZincWorkerImpl(ctx0: mill.util.Ctx,
   @volatile var mixedCompilersCache = Option.empty[(Long, Compilers)]
 
   def docJar(scalaVersion: String,
-             compilerBridgeSources: Path,
-             compilerClasspath: Agg[Path],
-             scalacPluginClasspath: Agg[Path],
+             compilerBridgeSources: os.Path,
+             compilerClasspath: Agg[os.Path],
+             scalacPluginClasspath: Agg[os.Path],
              args: Seq[String])
             (implicit ctx: mill.util.Ctx): Boolean = {
     val compilers: Compilers = prepareCompilers(
@@ -69,16 +68,16 @@ class ZincWorkerImpl(ctx0: mill.util.Ctx,
    *  TODO: Proper invalidation, see #389
    */
   def compileZincBridgeIfNeeded(scalaVersion: String,
-                                sourcesJar: Path,
-                                compilerJars: Array[File]): Path = {
+                                sourcesJar: os.Path,
+                                compilerJars: Array[File]): os.Path = {
     val workingDir = ctx0.dest / scalaVersion
     val compiledDest = workingDir / 'compiled
-    if (!exists(workingDir)) {
+    if (!os.exists(workingDir)) {
 
       ctx0.log.info("Compiling compiler interface...")
 
-      mkdir(workingDir)
-      mkdir(compiledDest)
+      os.makeDir.all(workingDir)
+      os.makeDir.all(compiledDest)
 
       val sourceFolder = mill.modules.Util.unpackZip(sourcesJar)(workingDir)
       val classloader = mill.util.ClassLoader.create(compilerJars.map(_.toURI.toURL), null)(ctx0)
@@ -91,7 +90,7 @@ class ZincWorkerImpl(ctx0: mill.util.Ctx,
       val argsArray = Array[String](
         "-d", compiledDest.toString,
         "-classpath", (compilerJars ++ compilerBridgeClasspath).mkString(File.pathSeparator)
-      ) ++ ls.rec(sourceFolder.path).filter(_.ext == "scala").map(_.toString)
+      ) ++ os.walk(sourceFolder.path).filter(_.ext == "scala").map(_.toString)
 
       compilerMain.getMethod("process", classOf[Array[String]])
         .invoke(null, argsArray)
@@ -116,8 +115,8 @@ class ZincWorkerImpl(ctx0: mill.util.Ctx,
   }
 
   def compileJava(upstreamCompileOutput: Seq[CompilationResult],
-                  sources: Agg[Path],
-                  compileClasspath: Agg[Path],
+                  sources: Agg[os.Path],
+                  compileClasspath: Agg[os.Path],
                   javacOptions: Seq[String])
                  (implicit ctx: mill.util.Ctx): mill.eval.Result[CompilationResult] = {
     compileInternal(
@@ -131,14 +130,14 @@ class ZincWorkerImpl(ctx0: mill.util.Ctx,
   }
 
   def compileMixed(upstreamCompileOutput: Seq[CompilationResult],
-                   sources: Agg[Path],
-                   compileClasspath: Agg[Path],
+                   sources: Agg[os.Path],
+                   compileClasspath: Agg[os.Path],
                    javacOptions: Seq[String],
                    scalaVersion: String,
                    scalacOptions: Seq[String],
-                   compilerBridgeSources: Path,
-                   compilerClasspath: Agg[Path],
-                   scalacPluginClasspath: Agg[Path])
+                   compilerBridgeSources: os.Path,
+                   compilerClasspath: Agg[os.Path],
+                   scalacPluginClasspath: Agg[os.Path])
                   (implicit ctx: mill.util.Ctx): mill.eval.Result[CompilationResult] = {
     val compilers: Compilers = prepareCompilers(
       scalaVersion,
@@ -158,9 +157,9 @@ class ZincWorkerImpl(ctx0: mill.util.Ctx,
   }
 
   private def prepareCompilers(scalaVersion: String,
-                               compilerBridgeSources: Path,
-                               compilerClasspath: Agg[Path],
-                               scalacPluginClasspath: Agg[Path])
+                               compilerBridgeSources: os.Path,
+                               compilerClasspath: Agg[os.Path],
+                               scalacPluginClasspath: Agg[os.Path])
                               (implicit ctx: mill.util.Ctx)= {
     val combinedCompilerClasspath = compilerClasspath ++ scalacPluginClasspath
     val combinedCompilerJars = combinedCompilerClasspath.toArray.map(_.toIO)
@@ -170,11 +169,11 @@ class ZincWorkerImpl(ctx0: mill.util.Ctx,
       compilerBridgeSources,
       compilerClasspath.toArray.map(_.toIO)
     )
-    val compilerBridgeSig = compilerBridge.mtime.toMillis
+    val compilerBridgeSig = os.mtime(compilerBridge)
 
     val compilersSig =
       compilerBridgeSig +
-        combinedCompilerClasspath.map(p => p.toString().hashCode + p.mtime.toMillis).sum
+        combinedCompilerClasspath.map(p => p.toString().hashCode + os.mtime(p)).sum
 
     val compilers = mixedCompilersCache match {
       case Some((k, v)) if k == compilersSig => v
@@ -205,13 +204,13 @@ class ZincWorkerImpl(ctx0: mill.util.Ctx,
   }
 
   private def compileInternal(upstreamCompileOutput: Seq[CompilationResult],
-                              sources: Agg[Path],
-                              compileClasspath: Agg[Path],
+                              sources: Agg[os.Path],
+                              compileClasspath: Agg[os.Path],
                               javacOptions: Seq[String],
                               scalacOptions: Seq[String],
                               compilers: Compilers)
                              (implicit ctx: mill.util.Ctx): mill.eval.Result[CompilationResult] = {
-    mkdir(ctx.dest)
+    os.makeDir.all(ctx.dest)
 
     val logger = {
       val consoleAppender = MainAppender.defaultScreen(ConsoleOut.printStreamOut(
diff --git a/scalanativelib/src/mill/scalanativelib/ScalaNativeModule.scala b/scalanativelib/src/mill/scalanativelib/ScalaNativeModule.scala
index c8d9abda..d8a282de 100644
--- a/scalanativelib/src/mill/scalanativelib/ScalaNativeModule.scala
+++ b/scalanativelib/src/mill/scalanativelib/ScalaNativeModule.scala
@@ -3,7 +3,6 @@ package scalanativelib
 
 import java.net.URLClassLoader
 
-import ammonite.ops.Path
 import coursier.Cache
 import coursier.maven.MavenRepository
 import mill.define.{Target, Task}
@@ -71,7 +70,7 @@ trait ScalaNativeModule extends ScalaModule { outer =>
     val workerKey = "MILL_SCALANATIVE_WORKER_" + scalaNativeBinaryVersion().replace('.', '_').replace('-', '_')
     val workerPath = sys.props(workerKey)
     if (workerPath != null)
-      Result.Success(Agg(workerPath.split(',').map(p => PathRef(Path(p), quick = true)): _*))
+      Result.Success(Agg(workerPath.split(',').map(p => PathRef(os.Path(p), quick = true)): _*))
     else
       Lib.resolveDependencies(
         Seq(Cache.ivy2Local, MavenRepository("https://repo1.maven.org/maven2")),
diff --git a/scalanativelib/src/mill/scalanativelib/ScalaNativeWorkerApi.scala b/scalanativelib/src/mill/scalanativelib/ScalaNativeWorkerApi.scala
index 05c3f7d7..be834e89 100644
--- a/scalanativelib/src/mill/scalanativelib/ScalaNativeWorkerApi.scala
+++ b/scalanativelib/src/mill/scalanativelib/ScalaNativeWorkerApi.scala
@@ -3,7 +3,6 @@ package mill.scalanativelib
 import java.io.File
 import java.net.URLClassLoader
 
-import ammonite.ops.Path
 import mill.define.{Discover, Worker}
 import mill.{Agg, T}
 import sbt.testing.Framework
@@ -12,8 +11,8 @@ import sbt.testing.Framework
 class ScalaNativeWorker {
   private var scalaInstanceCache = Option.empty[(Long, ScalaNativeWorkerApi)]
 
-  def impl(toolsClasspath: Agg[Path]): ScalaNativeWorkerApi = {
-    val classloaderSig = toolsClasspath.map(p => p.toString().hashCode + p.mtime.toMillis).sum
+  def impl(toolsClasspath: Agg[os.Path]): ScalaNativeWorkerApi = {
+    val classloaderSig = toolsClasspath.map(p => p.toString().hashCode + os.mtime(p)).sum
     scalaInstanceCache match {
       case Some((sig, bridge)) if sig == classloaderSig => bridge
       case _ =>
@@ -44,18 +43,18 @@ class ScalaNativeWorker {
 case class NativeConfig(config: Any)
 
 trait ScalaNativeWorkerApi {
-  def discoverClang: Path
-  def discoverClangPP: Path
-  def discoverTarget(clang: Path, workDir: Path): String
+  def discoverClang: os.Path
+  def discoverClangPP: os.Path
+  def discoverTarget(clang: os.Path, workDir: os.Path): String
   def discoverCompileOptions: Seq[String]
   def discoverLinkingOptions: Seq[String]
 
-  def config(nativeLibJar: Path,
+  def config(nativeLibJar: os.Path,
              mainClass: String,
-             classpath: Seq[Path],
-             nativeWorkdir: Path,
-             nativeClang: Path,
-             nativeClangPP: Path,
+             classpath: Seq[os.Path],
+             nativeWorkdir: os.Path,
+             nativeClang: os.Path,
+             nativeClangPP: os.Path,
              nativeTarget: String,
              nativeCompileOptions: Seq[String],
              nativeLinkingOptions: Seq[String],
@@ -65,7 +64,7 @@ trait ScalaNativeWorkerApi {
              logLevel: NativeLogLevel): NativeConfig
 
   def defaultGarbageCollector: String
-  def nativeLink(nativeConfig: NativeConfig, outPath: Path): Path
+  def nativeLink(nativeConfig: NativeConfig, outPath: os.Path): os.Path
 
   def newScalaNativeFrameWork(framework: Framework, id: Int, testBinary: File,
                               logLevel: NativeLogLevel, envVars: Map[String, String]): Framework
diff --git a/scalanativelib/test/src/mill/scalanativelib/HelloNativeWorldTests.scala b/scalanativelib/test/src/mill/scalanativelib/HelloNativeWorldTests.scala
index 4c67b98f..37fbfc80 100644
--- a/scalanativelib/test/src/mill/scalanativelib/HelloNativeWorldTests.scala
+++ b/scalanativelib/test/src/mill/scalanativelib/HelloNativeWorldTests.scala
@@ -2,7 +2,6 @@ package mill.scalanativelib
 
 import java.util.jar.JarFile
 
-import ammonite.ops._
 import mill._
 import mill.define.Discover
 import mill.eval.{Evaluator, Result}
@@ -73,7 +72,7 @@ object HelloNativeWorldTests extends TestSuite {
     override lazy val millDiscover = Discover[this.type]
   }
 
-  val millSourcePath = pwd / 'scalanativelib / 'test / 'resources / "hello-native-world"
+  val millSourcePath = os.pwd / 'scalanativelib / 'test / 'resources / "hello-native-world"
 
   val helloWorldEvaluator = TestEvaluator.static(HelloNativeWorld)
 
@@ -90,7 +89,7 @@ object HelloNativeWorldTests extends TestSuite {
           helloWorldEvaluator(HelloNativeWorld.helloNativeWorld(scalaVersion, scalaNativeVersion, mode).compile)
 
         val outPath = result.classes.path
-        val outputFiles = ls.rec(outPath).filter(_.isFile)
+        val outputFiles = os.walk(outPath).filter(os.isFile)
         val expectedClassfiles = compileClassfiles(outPath / 'hello)
         assert(
           outputFiles.toSet == expectedClassfiles,
@@ -185,7 +184,7 @@ object HelloNativeWorldTests extends TestSuite {
         helloWorldEvaluator.outPath,
         task.ctx.segments
       )
-      val log = read(paths.log)
+      val log = os.read(paths.log)
       assert(
         evalCount > 0,
         log.contains("Scala Native")
@@ -198,7 +197,7 @@ object HelloNativeWorldTests extends TestSuite {
     }
   }
 
-  def compileClassfiles(parentDir: Path) = Set(
+  def compileClassfiles(parentDir: os.Path) = Set(
     parentDir / "ArgsParser$.class",
     parentDir / "ArgsParser$.nir",
     parentDir / "ArgsParser.class",
@@ -210,8 +209,8 @@ object HelloNativeWorldTests extends TestSuite {
   )
 
   def prepareWorkspace(): Unit = {
-    rm(workspacePath)
-    mkdir(workspacePath / up)
-    cp(millSourcePath, workspacePath)
+    os.remove.all(workspacePath)
+    os.makeDir.all(workspacePath / os.up)
+    os.copy(millSourcePath, workspacePath)
   }
 }
diff --git a/scalanativelib/worker/0.3/src/mill/scalanativelib/worker/ScalaNativeWorkerImpl.scala b/scalanativelib/worker/0.3/src/mill/scalanativelib/worker/ScalaNativeWorkerImpl.scala
index 7e93fbd4..8c24a39e 100644
--- a/scalanativelib/worker/0.3/src/mill/scalanativelib/worker/ScalaNativeWorkerImpl.scala
+++ b/scalanativelib/worker/0.3/src/mill/scalanativelib/worker/ScalaNativeWorkerImpl.scala
@@ -4,7 +4,6 @@ import java.io.File
 import java.lang.System.{err, out}
 
 import scala.scalanative.build.{Build, Config, Discover, GC, Logger, Mode}
-import ammonite.ops.Path
 import mill.scalanativelib.{NativeConfig, NativeLogLevel, ReleaseMode}
 import sbt.testing.Framework
 
@@ -19,19 +18,19 @@ class ScalaNativeWorkerImpl extends mill.scalanativelib.ScalaNativeWorkerApi {
       warnFn  = msg => if (level >= NativeLogLevel.Warn)  out.println(msg),
       errorFn = msg => if (level >= NativeLogLevel.Error) err.println(msg))
 
-  def discoverClang: Path = Path(Discover.clang())
-  def discoverClangPP: Path = Path(Discover.clangpp())
-  def discoverTarget(clang: Path, workdir: Path): String = Discover.targetTriple(clang.toNIO, workdir.toNIO)
+  def discoverClang: os.Path = os.Path(Discover.clang())
+  def discoverClangPP: os.Path = os.Path(Discover.clangpp())
+  def discoverTarget(clang: os.Path, workdir: os.Path): String = Discover.targetTriple(clang.toNIO, workdir.toNIO)
   def discoverCompileOptions: Seq[String] = Discover.compileOptions()
   def discoverLinkingOptions: Seq[String] = Discover.linkingOptions()
   def defaultGarbageCollector: String = GC.default.name
 
-  def config(nativeLibJar: Path,
+  def config(nativeLibJar: os.Path,
              mainClass: String,
-             classpath: Seq[Path],
-             nativeWorkdir: Path,
-             nativeClang: Path,
-             nativeClangPP: Path,
+             classpath: Seq[os.Path],
+             nativeWorkdir: os.Path,
+             nativeClang: os.Path,
+             nativeClangPP: os.Path,
              nativeTarget: String,
              nativeCompileOptions: Seq[String],
              nativeLinkingOptions: Seq[String],
@@ -60,7 +59,7 @@ class ScalaNativeWorkerImpl extends mill.scalanativelib.ScalaNativeWorkerApi {
       NativeConfig(config)
     }
 
-  def nativeLink(nativeConfig: NativeConfig, outPath: Path): Path = {
+  def nativeLink(nativeConfig: NativeConfig, outPath: os.Path): os.Path = {
     val config = nativeConfig.config.asInstanceOf[Config]
     Build.build(config, outPath.toNIO)
     outPath