Python Which/Where - Find executable

find_executable.py

#!/usr/bin/env python

# https://gist.github.com/4368898
# Public domain code by anatoly techtonik <techtonik@gmail.com>
# AKA Linux `which` and Windows `where`

# For Python 3 you probably want
# https://docs.python.org/dev/library/shutil.html#shutil.which

import os
import sys

def find_executable(executable, path=None):
    """Find if 'executable' can be run. Looks for it in 'path'
    (string that lists directories separated by 'os.pathsep';
    defaults to os.environ['PATH']). Checks for all executable
    extensions. Returns full path or None if no command is found.
    """
    if path is None:
        path = os.environ['PATH']
    paths = path.split(os.pathsep)
    extlist = ['']
    if os.name == 'os2':
        (base, ext) = os.path.splitext(executable)
        # executable files on OS/2 can have an arbitrary extension, but
        # .exe is automatically appended if no dot is present in the name
        if not ext:
            executable = executable + ".exe"
    elif sys.platform == 'win32':
        pathext = os.environ['PATHEXT'].lower().split(os.pathsep)
        (base, ext) = os.path.splitext(executable)
        if ext.lower() not in pathext:
            extlist = pathext
        # Windows looks for binaries in current dir first
        paths.insert(0, '')

    for ext in extlist:
        execname = executable + ext
        for p in paths:
            f = os.path.join(p, execname)
            if os.path.isfile(f):
                return f
    else:
        return None

if __name__ == '__main__':
    if sys.argv[1:]:
        print(find_executable(sys.argv[1]))
    else:
        print('usage: find_executable.py <progname>')

Hi! Can I suggest a patch?

0a1,2
> #!/usr/bin/env python
> 
41c43,44
< # print find_executable('hg')
---
> if __name__ == '__main__':
>     print(find_executable('git'))

You should not automatically check for executable in the current working directory. This makes it too easy for the user to accidentally execute a trojan. Users who really really trust their environment can explicitly add "." to their search PATH if they wish but it is a bad idea.

In short, remove "if os.path.isfile(execname)" and use only the contents of the else block.

As of Python 3.3 there is also shutil.which.

For python 2 there is from distutils.spawn.find_executable, the only weirdness is that on windows it will capitalize the extension.

is there any way to make it look in deeper paths? so it would check the whole C DRIVE?

@phdru thanks for the suggestion. Added shebang and command line argument for easy testing with different names.

@KeithHanlan good catch. I was probably writing it from Windows, where it was the default system behavior. There is no point to port this insecurity to Linux.

@KeithHanlan the security issue is now fixed. The old behavior is preserved only for Windows.

@sergio44k you need a standard code for recursive directory search. https://stackoverflow.com/questions/2186525/how-to-use-glob-to-find-files-recursively should help.

@rth
As of Python 3.3 there is also shutil.which.

The most valuable comment for me. The entire solution is just to call shutil.which.

Added a link to shutil.which for Python 3 users.