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.

This is a fork of the original which module that I wrote in 2011, because that became the property of npm, and I wanted a hybrid CommonJS/ESM typescript implementation, which doesn't align with the npm team's needs.

I'm ok with the fork continuing to exist. It is fine for different parties to have different priorities. This is a small module, and it does no harm to have multiple copies in the world.

import { which, whichSync } from '@isaacs/which'

// async usage
// rejects if not found
const resolved = await which('node')

// if nothrow option is used, returns null if not found
const resolvedOrNull = await which('node', { nothrow: true })

// sync usage
// throws if not found
const resolved = whichSync('node')

// if nothrow option is used, returns null if not found
const resolvedOrNull = whichSync('node', { nothrow: true })

// Pass options to override the PATH and PATHEXT environment vars.
await which('node', { path: someOtherPath, pathExt: somePathExt })

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.