The 'which' npm package is a simple utility to locate a command in the user's path, similar to the Unix 'which' command. It is used to find the first instance of a specified executable in the system path, which can be useful for ensuring that a required command-line tool is available and for invoking system commands from Node.js scripts.

What are which's main functionalities?

Synchronous command search

This feature allows you to synchronously find the path to an executable in the system's PATH. The 'sync' method returns the path to the specified executable if it exists.

const which = require('which');
const cmdPath = which.sync('node');
console.log(`Node.js is located at: ${cmdPath}`);

Asynchronous command search

This feature allows you to asynchronously find the path to an executable in the system's PATH. The 'which' function takes a callback that receives the path to the specified executable if it exists.

const which = require('which');
which('node', function (err, cmdPath) {
  if (err) throw err;
  console.log(`Node.js is located at: ${cmdPath}`);
});

Throw on not found

This feature allows you to specify whether the 'which' method should throw an error if the command is not found. By default, or when 'nothrow' is set to false, it will throw an error.

const which = require('which');
try {
  const cmdPath = which.sync('unknown-command', {nothrow: false});
} catch (e) {
  console.error('Command not found');
}

Other packages similar to which

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Source

which

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.

USAGE

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
})

// or promise
which('node').then(resolvedPath => { ... }).catch(er => { ... not found ... })

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

// if nothrow option is used, returns null if not found
resolved = which.sync('node', {nothrow: true})

// 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)
})

CLI USAGE

Same as the BSD which(1) binary.

usage: which [-as] program ...

OPTIONS

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.

FAQs

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Last updated on 18 Nov 2019

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