File manager

# 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

```javascript
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')

// 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.