squish-squash/src/sh-overrider.js

overrides a system or user command for for all child processes

var CMD_OVERRIDE_BASE = 'SQUISH_SQUASH'
var CMD_OVERRIDE_COUNT = 0
var ss = require('child_process').spawnSync
var path = require('path')
var assign = require('lodash.assign')
var ostmpdir = require('os-tmpdir')
var crypto = require('crypto')
var fs = require('fs')

/**
 * temporarily squash some other command.
 * this is similar to using a bash `alias`, but doesn't modify the user's env,
 * instead, just the process' env
 * @ref http://stackoverflow.com/questions/34100700/temporary-alias-a-cmd-to-squash-an-existing-command-then-expire-upon-script-exi
 * @param {object}  opts
 * @param {object}  opts.squash  name of command to squash, e.g. `ls`
 * @param {string=} opts.syscmd  command to squash with, available in the
 *                               existing env. e.g. `ls -al`
 * @param {string=} opts.cmdpath /path/to/binary to use instead of the `squash`ed binary
 * @return {undefined}
 */
module.exports = function (opts) {
  var CMD_OVERRIDE_DIR = CMD_OVERRIDE_BASE + '_' + CMD_OVERRIDE_COUNT.toString()
  ++CMD_OVERRIDE_COUNT
  var cmdpath

  if (!opts.squash) {
    throw new ReferenceError('`squash` property must be provided')
  }
  if (typeof opts.cmdpath === 'string') {
    cmdpath = opts.cmdpath
  } else if (typeof opts.syscmd === 'string') {
    cmdpath = ss('which', [opts.syscmd])
    cmdpath = cmdpath.stdout.toString().match(/.*[a-zA-Z]/)[0]
  } else {
    throw new ReferenceError('expected cmdpath or syscmd props')
  }

  // build temp dir that we will make a sym link to our desired squash cmd
  var tmpdir = path.join(
    ostmpdir(),
    CMD_OVERRIDE_DIR + '_' + crypto.randomBytes(5).toString('hex')
  )
  fs.mkdirSync(tmpdir)

  // update env with new PATH to our temporary binary squashing dir
  process.env = assign({}, process.env, { 'PATH': tmpdir + ':' + process.env.PATH })

  var linkSrc = path.resolve(cmdpath)
  var linkTarget = path.resolve(tmpdir, opts.squash)
  var linkResult = ss('ln', ['-s', linkSrc, linkTarget], { stdio: 'inherit' })

  // assert that the temp dir and link will be removed when our child process exits
  var tidyup = function () {
    fs.unlinkSync(path.join(tmpdir, opts.squash))
    fs.rmdirSync(tmpdir)
  }
  process.on('exit', tidyup)

  return {
    src: linkSrc,
    target: linkTarget
  }
}