|                                                      |  | # which
Like the unix `which` utility.
Finds the first instance of a specified executable in the PATHenvironment variable.  Does not cache the results, so `hash -r` is notneeded when the PATH changes.
## USAGE
```javascriptvar which = require('which')
// async usagewhich('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 promisewhich('node').then(resolvedPath => { ... }).catch(er => { ... not found ... })
// sync usage// throws if not foundvar resolved = which.sync('node')
// if nothrow option is used, returns null if not foundresolved = 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.
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