diff --git a/src/io/file_output.ts b/src/io/file_output.ts
index e970a07..890253b 100644
--- a/src/io/file_output.ts
+++ b/src/io/file_output.ts
@@ -1,28 +1,25 @@
 import { BufferedOutput } from "./buffered_output"
-//import { IFileSystem } from "../file_system"
+import { IFileSystem } from "../file_system"
 
 export class FileOutput extends BufferedOutput {
-  //constructor(fs: IFileSystem, path: string, append: boolean) {
-  constructor(path: string, append: boolean) {
+  constructor(readonly fileSystem: IFileSystem, readonly path: string, readonly append: boolean) {
     super()
-    //this.fs = fs
-    this.path = path
-    this.append = append
+  }
 
-    console.log(this.path)
+  override async flush(): Promise<void> {
+    const { FS } = this.fileSystem
+    let content = this.data.join("")
 
     if (this.append) {
-      throw Error("FileOutput in append mode not implemented")
+      try {
+        const prevContent = FS.readFile(this.path, { "encoding": "utf8" })
+        content = prevContent + content
+      } catch (e) {
+        // If file does not exist, fallback to write (non-append) behaviour.
+      }
     }
-  }
 
-  override async flush(): Promise<void> {
-    //const all_data = this.data.join()
-    //this.fs.write(this.path, all_data)
+    FS.writeFile(this.path, content)
     this.clear()
   }
-
-  //private readonly fs: IFileSystem
-  private readonly path: string
-  private readonly append: boolean  // or replace
 }
diff --git a/src/parse.ts b/src/parse.ts
index cff09aa..e09d264 100644
--- a/src/parse.ts
+++ b/src/parse.ts
@@ -78,12 +78,12 @@ function _createCommandNode(tokens: Token[]) {
   let args = tokens.slice(1)
 
   // Handle redirects.
-  const index = args.findIndex((token) => token.value == ">")
+  const index = args.findIndex((token) => token.value.startsWith(">"))
   if (index >= 0) {
     // Must support multiple redirects for a single command.
     if (args.length != index + 2) {
       // Need better error handling here.
-      throw Error("Redirect should be followed by file to redirect to")
+      throw new Error("Redirect should be followed by file to redirect to")
     }
     const redirect = new RedirectNode(args[index], args[index+1])
     args = args.slice(0, index)
diff --git a/src/shell.ts b/src/shell.ts
index 0d5cf58..8ff4d2f 100644
--- a/src/shell.ts
+++ b/src/shell.ts
@@ -1,7 +1,7 @@
 import { CommandRegistry } from "./command_registry"
 import { Context } from "./context"
 import { IFileSystem } from "./file_system"
-import { TerminalOutput } from "./io"
+import { FileOutput, Output, TerminalOutput } from "./io"
 import { IOutputCallback } from "./output_callback"
 import { CommandNode, parse } from "./parse"
 import * as FsModule from './wasm/fs'
@@ -93,23 +93,40 @@ export class Shell {
 
   // Keeping this public for tests.
   async _runCommands(cmdText: string): Promise<void> {
-    const cmdNodes = parse(cmdText)
-    const ncmds = cmdNodes.length
     const stdout = new TerminalOutput(this._outputCallback)
     try {
+      const cmdNodes = parse(cmdText)
+      const ncmds = cmdNodes.length
+
       for (let i = 0; i < ncmds; ++i) {
         const command = cmdNodes[i] as CommandNode
         const cmdName = command.name.value
 
-        const commands = CommandRegistry.instance().get(cmdName)
-        if (commands === null) {
+        const runner = CommandRegistry.instance().get(cmdName)
+        if (runner === null) {
           // Give location of command in input?
           throw new Error(`Unknown command: '${cmdName}'`)
         }
 
+        let output: Output = stdout
+        if (command.redirects) {
+          // Support single redirect only, write or append to file.
+          if (command.redirects.length > 1) {
+            throw new Error("Only implemented a single redirect per command")
+          }
+          const redirect = command.redirects[0]
+          const redirectChars = redirect.token.value
+          if (!(redirectChars == ">" || redirectChars == ">>")) {
+            throw new Error("Only implemented redirect write to file, not " + redirectChars)
+          }
+
+          const path = redirect.target.value
+          output = new FileOutput(this._fileSystem!, path, redirectChars == ">>")
+        }
+
         const args = command.suffix.map((token) => token.value)
-        const context = new Context(args, this._fileSystem!, this._mountpoint, stdout)
-        await commands.run(cmdName, context)
+        const context = new Context(args, this._fileSystem!, this._mountpoint, output)
+        await runner.run(cmdName, context)
 
         await context.flush()
       }
diff --git a/src/tokenize.ts b/src/tokenize.ts
index db02972..60313ee 100644
--- a/src/tokenize.ts
+++ b/src/tokenize.ts
@@ -13,28 +13,29 @@ export function tokenize(source: string): Token[] {
   let offset: number = -1  // Offset of start of current token, -1 if not in token.
   const n = source.length
 
+  let prevChar: string = ""
+  let prevCharType: CharType = CharType.None
   for (let i = 0; i < n; i++) {
     const char = source[i]
+    const charType = _getCharType(char)
     if (offset >= 0) {  // In token.
-      if (whitespace.includes(char)) {
+      if (charType == CharType.Whitespace) {
         // Finish current token.
         tokens.push({offset, value: source.slice(offset, i)})
         offset = -1
-      } else if (delimiters.includes(char)) {
-        // Finish current token and create new one for delimiter.
+      } else if (charType != prevCharType || (charType == CharType.Delimiter && char != prevChar)) {
+        // Finish current token and start new one.
         tokens.push({offset, value: source.slice(offset, i)})
-        tokens.push({offset: i, value: source.slice(i, i+1)})
-        offset = -1
+        offset = i
       }
     } else {  // Not in token.
-      if (delimiters.includes(char)) {
-        // Single character delimiter.
-        tokens.push({offset: i, value: source.slice(i, i+1)})
-      } else if (!whitespace.includes(char)) {
+      if (charType != CharType.Whitespace) {
         // Start new token.
         offset = i
       }
     }
+    prevChar = char
+    prevCharType = charType
   }
 
   if (offset >= 0) {
@@ -44,3 +45,20 @@ export function tokenize(source: string): Token[] {
 
   return tokens
 }
+
+enum CharType {
+  None,
+  Delimiter,
+  Whitespace,
+  Other,
+}
+
+function _getCharType(char: string): CharType {
+  if (whitespace.includes(char)) {
+    return CharType.Whitespace
+  } else if (delimiters.includes(char)) {
+    return CharType.Delimiter
+  } else {
+    return CharType.Other
+  }
+}
diff --git a/tests/commands/cat.test.ts b/tests/commands/cat.test.ts
index 00e7d02..8135db8 100644
--- a/tests/commands/cat.test.ts
+++ b/tests/commands/cat.test.ts
@@ -1,6 +1,6 @@
 import { shell_setup_simple } from "../shell_setup"
 
-describe("echo command", () => {
+describe("cat command", () => {
   it("should write to stdout", async () => {
     const { shell, output } = await shell_setup_simple()
     await shell._runCommands("cat file1")
diff --git a/tests/commands/grep.test.ts b/tests/commands/grep.test.ts
new file mode 100644
index 0000000..152b605
--- /dev/null
+++ b/tests/commands/grep.test.ts
@@ -0,0 +1,27 @@
+import { shell_setup_simple } from "../shell_setup"
+
+describe("grep command", () => {
+  it("should write to stdout", async () => {
+    const { shell, output } = await shell_setup_simple()
+    await shell._runCommands("grep cond file2")
+    expect(output.text).toEqual("Second line\r\n")
+  })
+
+  it("should support ^ and $", async () => {
+    const { shell, output, FS } = await shell_setup_simple()
+    const line0 = " hello"
+    const line1 = "hello "
+    FS.writeFile("file3", line0 + "\n" + line1)
+
+    await shell._runCommands("grep hello file3")
+    expect(output.text).toEqual(line0 + "\r\n" + line1 + "\r\n")
+    output.clear()
+
+    await shell._runCommands("grep ^hello file3")
+    expect(output.text).toEqual(line1 + "\r\n")
+    output.clear()
+
+    await shell._runCommands("grep hello$ file3")
+    expect(output.text).toEqual(line0 + "\r\n")
+  })
+})
diff --git a/tests/file_system_setup.ts b/tests/file_system_setup.ts
deleted file mode 100644
index 5ddffba..0000000
--- a/tests/file_system_setup.ts
+++ /dev/null
@@ -1,15 +0,0 @@
-import { ContentsManagerMock } from "@jupyterlab/services/lib/testutils"
-import { IFileSystem } from "../src"
-import { JupyterFileSystem } from "../src/jupyter_file_system"
-
-export async function file_system_setup(name: string): Promise<IFileSystem> {
-  if (name == "jupyter") {
-    const cm = new ContentsManagerMock()
-    await cm.save("file1", {content: "Contents of file1"})
-    await cm.save("file2")
-    await cm.save("dirA", { type: "directory" })
-    return new JupyterFileSystem(cm)
-  } else {
-    throw Error("No other IFileSystem-derived classes supported")
-  }
-}
diff --git a/tests/parse.test.ts b/tests/parse.test.ts
index f7b5412..85dfa16 100644
--- a/tests/parse.test.ts
+++ b/tests/parse.test.ts
@@ -69,4 +69,9 @@ describe("parse", () => {
         [new RedirectNode({offset: 5, value: ">"}, {offset: 6, value: "file"})])
     ])
   })
+
+  it("should raise on redirect without target file", () => {
+    expect(() => parse("ls >")).toThrow("file to redirect to")
+    expect(() => parse("ls >>")).toThrow("file to redirect to")
+  })
 })
diff --git a/tests/shell.test.ts b/tests/shell.test.ts
index 018f1da..8e825e6 100644
--- a/tests/shell.test.ts
+++ b/tests/shell.test.ts
@@ -13,6 +13,17 @@ describe("Shell", () => {
       await shell._runCommands("   ls")
       expect(output.text).toEqual("dirA  file1  file2\r\n")
     })
+
+    it("should output to file", async () => {
+      const { shell, output, FS } = await shell_setup_simple()
+      await shell._runCommands("echo Hello > out")
+      expect(output.text).toEqual("")
+      expect(FS.readFile("out", { "encoding": "utf8" })).toEqual("Hello\n")
+
+      await shell._runCommands("echo Goodbye >> out")
+      expect(output.text).toEqual("")
+      expect(FS.readFile("out", { "encoding": "utf8" })).toEqual("Hello\nGoodbye\n")
+    })
   })
 
   describe("input", () => {
diff --git a/tests/tokenize.test.ts b/tests/tokenize.test.ts
index 6064d42..84cb87d 100644
--- a/tests/tokenize.test.ts
+++ b/tests/tokenize.test.ts
@@ -30,25 +30,22 @@ describe("Tokenize", () => {
     expect(tokenize("ls;")).toEqual([{offset: 0, value: "ls"}, {offset: 2, value: ";"}])
     expect(tokenize(";ls")).toEqual([{offset: 0, value: ";"}, {offset: 1, value: "ls"}])
     expect(tokenize(";ls;;")).toEqual([
-      {offset: 0, value: ";"}, {offset: 1, value: "ls"}, {offset: 3, value: ";"},
-      {offset: 4, value: ";"},
+      {offset: 0, value: ";"}, {offset: 1, value: "ls"}, {offset: 3, value: ";;"},
     ])
     expect(tokenize("ls ; ; pwd")).toEqual([
       {offset: 0, value: "ls"}, {offset: 3, value: ";"}, {offset: 5, value: ";"},
       {offset: 7, value: "pwd"},
     ])
     expect(tokenize("ls ;; pwd")).toEqual([
-      {offset: 0, value: "ls"}, {offset: 3, value: ";"}, {offset: 4, value: ";"},
-      {offset: 6, value: "pwd"},
+      {offset: 0, value: "ls"}, {offset: 3, value: ";;"}, {offset: 6, value: "pwd"},
     ])
     expect(tokenize("ls;pwd")).toEqual([
       {offset: 0, value: "ls"}, {offset: 2, value: ";"}, {offset: 3, value: "pwd"},
     ])
     expect(tokenize("ls;;pwd")).toEqual([
-      {offset: 0, value: "ls"}, {offset: 2, value: ";"}, {offset: 3, value: ";"},
-      {offset: 4, value: "pwd"},
+      {offset: 0, value: "ls"}, {offset: 2, value: ";;"}, {offset: 4, value: "pwd"},
     ])
-    expect(tokenize(" ;; ")).toEqual([{offset: 1, value: ";"}, {offset: 2, value: ";"}])
+    expect(tokenize(" ;; ")).toEqual([{offset: 1, value: ";;"}])
     expect(tokenize(" ; ; ")).toEqual([{offset: 1, value: ";"}, {offset: 3, value: ";"}])
   })
 
@@ -72,5 +69,17 @@ describe("Tokenize", () => {
       {offset: 0, value: "ls"}, {offset: 3, value: "-l"}, {offset: 5, value: ">"},
       {offset: 6, value: "somefile"},
     ])
+    expect(tokenize("ls >> somefile")).toEqual([
+      {offset: 0, value: "ls"}, {offset: 3, value: ">>"}, {offset: 6, value: "somefile"},
+    ])
+    expect(tokenize("ls>>somefile")).toEqual([
+      {offset: 0, value: "ls"}, {offset: 2, value: ">>"}, {offset: 4, value: "somefile"},
+    ])
+    expect(tokenize("ls >>somefile")).toEqual([
+      {offset: 0, value: "ls"}, {offset: 3, value: ">>"}, {offset: 5, value: "somefile"},
+    ])
+    expect(tokenize("ls>> somefile")).toEqual([
+      {offset: 0, value: "ls"}, {offset: 2, value: ">>"}, {offset: 5, value: "somefile"},
+    ])
   })
 })