Retrieving the full path of Unix apps

[Andrew Dalke]

Lorin Hochstein wrote:
> I'd like to retrieve the full path of an arbitrary program on a Unix 
> system (e.g. gcc). What's the nicest way to do this? Currently I'm 
> invoking the "which" program and parsing what it outputs to determine if 
> the output looks like a path.

Here's an incomplete implementation of 'which'

import os

def is_executable(filename):
      # Placeholder: not sure how to do this
      return 1

def which(app):
      dirnames = os.environ["PATH"].split(os.path.pathsep)
      for dirname in dirnames:
           filename = os.path.join(dirname, app)
           if (os.path.exists(filename) and
               os.path.isfile(filename) and
               is_executable(filename)):
                return filename
      return None

 >>> print which("ls")
/bin/ls
 >>> print which("qwerty")
None
 >>> print which("python")
/usr/local/bin/python
 >>>

				Andrew
				dalke at dalkescientific.com