1.0.16 • Public • Published


    Shell Harness provides an easy way to interact with shell commands and scripts. Benefits:

    • an initial script can be run to set context for all subsequent commands
    • all commands run in a long-running Child Processes vs. a Child Processes for each command. This can be significantly faster than spawning new processes for each command. 36 times faster in one benchmark.
    • Multiple shells can be spawned to run commands in parallel
    • Commands are queued in a FIFO manner


    npm install @trevthedev/shell-harness

    How To

    Launch a shell(s)

    import ShellHarness from '@trevthedev/shell-harness'
    const shell = new ShellHarness()

    Send a command

    const cmd = await shell.createCommand('printf HELLO ;')
    console.log(cmd.output) // HELLO

    All shell commands or scripts must terminate with a semi-colon ;

    All stderr output is redirected to stdout via 2>&1 and not command should send data to stderr (required as Node does not process stdout and stderr sequentially)

    Send a command to all shells

    const cmd = await shell.createCommand('cd / ;', undefined, undefined, true)

    returns a promise that will resolve once the command has been executed on all shells ;

    Interact with the shell

    const cmdline = shell.interact('echo "what is your name?" ; read name;\n')
    cmdline.on('data', stdout => {
      if (stdout === 'what is your name?\n') {
        cmdline.stdin.write('Bob\necho $name\n ')
        cmdline.sendDoneMarker() // required to indicate that this interaction is completed
      } else {
        console.log(stdout) // `Bob\n`
    const outcome = await cmdline
    console.log(outcome.output) // `what is your name?\nBob\n`

    Get a root or other user shell

    const rootShell = new ShellHarness({
      user: 'root', // or other user
      rootPassword: process.env.RPASSWORD
    const cmd = await rootShell.createCommand('whoami;')
    console.log(cmd.output) // 'root\n'
    console.log(rootShell.config.rootPassword) // undefined

    This will switch to another user via sudo and a sudo'er password is required - unfortunately shell does not allow one to su without sudo.

    Intercept and replace output

    The output from a command can be intercepted in two ways and different result substituted if required.

    const cb = (cmdX, cbData) => {
      console.log(cbData) // 'HIT'
      return true
    const cmd = await shell.createCommand('printf HELLO ;', 'HIT', cb)
    console.log(cmd) // true


    const cb = (cmdX, cbData) => {
      console.log(cbData) // 'HIT'
      return true
    const cbShell = new ShellHarness({
      doneCallback: cb
    const cmd = await cbShell.createCommand('printf HELLO ;', 'HIT')
    console.log(cmd) // true

    Receive data via IPC

    const cmd = shell.interact(
      'printf "{\\"ipc\\": \\"true\\"}\\n" 1>&$NODE_CHANNEL_FD ; printf HELLO ; \n'
    cmd.on('message', data => {
      console.log(data) // { ipc: "true" }
      cmd.sendDoneMarker() // required to finished command
    const res = await cmd
    console.log(res.output) // `HELLO`

    Send data via IPC

    const cmd = shell.interact('echo ; \n')
    cmd.on('data', stdout => {
      if (stdout === '\n') {
        cmd.stdin.write('read -r line <&3 ; printf $line ; \n')
      } else cmd.sendDoneMarker() // required to finished command
    const res = await cmd
    console.log(res.output) // \n"HELLOBOB"`

    Node formats messages sent via IPC


      shell: '/bin/sh',        // shell to use
      initScript: undefined,   // script to run when shell is first launched
      doneCallback: undefined, // callback before any command is completed
      user: undefined,         // user to switch to via sudo then su
      rootPassword: undefined, // root password to switch user
      numberOfProcesses: 1,    // number of shells to spawn
      concurrentCmds: 100,     // max number of commands to send to the shell at a time per shell
      doneMarker: '__done__',  // unique identifier to determine whether command is completed - a sequential number is also added
      log: true                // produce a log


    const shell = new ShellHarness(optionalConfig)
    const cmd = shell.createCommand(
    const cmd = shell.interact(
    cmd.on('data', data => {})
    cmd.on('message', message => {})
    // other events include: created, enqueued, executing, cancelled, failed and finished
    const result = await cmd
    // result = {
    //  error: whether shell exited in error,
    //  command: the command sent,
    //  output: string result }


    npm i @trevthedev/shell-harness

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