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Like which(1) unix command. Find the first instance of an executable in the PATH.
Latest commit 3e04935 @isaacs isaacs doc cli


Like the unix which utility.

Finds the first instance of a specified executable in the PATH environment variable. Does not cache the results, so hash -r is not needed when the PATH changes.


var which = require('which')

// async usage
which('node', function (er, resolvedPath) {
  // er is returned if no "node" is found on the PATH
  // if it is found, then the absolute path to the exec is returned

// sync usage
// throws if not found
var resolved = which.sync('node')

// Pass options to override the PATH and PATHEXT environment vars.
which('node', { path: someOtherPath }, function (er, resolved) {
  if (er)
    throw er
  console.log('found at %j', resolved)


Same as the BSD which(1) binary.

usage: which [-as] program ...


You may pass an options object as the second argument.

  • path: Use instead of the PATH environment variable.
  • pathExt: Use instead of the PATHEXT environment variable.
  • all: Return all matches, instead of just the first one. Note that this means the function returns an array of strings instead of a single string.
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