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  • Re: Find the path of a shell command (shutil.which)

    From Weatherby,Gerard@21:1/5 to Paulo da Silva on Wed Oct 12 21:44:19 2022
    Not going to do any good if its not on the PATH in the first place:

    https://docs.python.org/3/library/shutil.html

    shutil.which(cmd, mode=os.F_OK | os.X_OK, path=None)
    Return the path to an executable which would be run if the given cmd was called. If no cmd would be called, return None.
    mode is a permission mask passed to os.access()<https://docs.python.org/3/library/os.html#os.access>, by default determining if the file exists and executable.
    When no path is specified, the results of os.environ()<https://docs.python.org/3/library/os.html#os.environ> are used, returning either the PATH value or a fallback of os.defpath<https://docs.python.org/3/library/os.html#os.defpath>.


    From: Python-list <python-list-bounces+gweatherby=uchc.edu@python.org> on behalf of Thomas Passin <list1@tompassin.net>
    Date: Wednesday, October 12, 2022 at 5:39 PM
    To: python-list@python.org <python-list@python.org>
    Subject: Re: Find the path of a shell command
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    On 10/12/2022 12:00 AM, Paulo da Silva wrote:
    Hi!

    The simple question: How do I find the full path of a shell command
    (linux), i.e. how do I obtain the corresponding of, for example,
    "type rm" in command line?

    The reason:
    I have python program that launches a detached rm. It works pretty well
    until it is invoked by cron! I suspect that for cron we need to specify
    the full path.
    Of course I can hardcode /usr/bin/rm. But, is rm always in /usr/bin?
    What about other commands?

    Thanks for any comments/responses.
    Paulo


    Python has a command that usually does the job:

    import shutil, os
    executable_path = shutil.which(exename, os.X_OK)

    If you know that the executable you want is on some non-standard path,
    you can or them together:

    executable_path = shutil.which(exename, os.X_OK)\
    or shutil.which(exename, os.X_OK, other_path)

    Presumably the shutil command uses which behind the scenes, but that
    doesn't matter.

    Now you can include this location when you run the executable from
    Python. If you need to run a system command from a batch file and not
    from Python, you will either need to have the right path in effect when
    the batch file is run, or manually include the full path to the file in
    the batch file.

    BTW, on Linux Mint, which is derived from Ubuntu and Debian, rm is at

    $ which rm
    /bin/rm



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  • From Eryk Sun@21:1/5 to Gerard on Wed Oct 12 17:14:45 2022
    On 10/12/22, Weatherby,Gerard <gweatherby@uchc.edu> wrote:

    When no path is specified, the results of os.environ()<https://docs.python.org/3/library/os.html#os.environ> are used, returning either the “PATH” value or a fallback of os.defpath<https://docs.python.org/3/library/os.html#os.defpath>.

    The documentation is out of sync with what the code actually does.
    os.defpath is hard coded in posixpath and ntpath, but shutil.which()
    actually prefers to query the system's default path to use via
    os.confstr(), if it's supported:

    if path is None:
    path = os.environ.get("PATH", None)
    if path is None:
    try:
    path = os.confstr("CS_PATH")
    except (AttributeError, ValueError):
    # os.confstr() or CS_PATH is not available
    path = os.defpath

    As documented by POSIX, the CS_PATH string "can be used as a value of
    the PATH environment variable that accesses all of the standard
    utilities of POSIX.1-2017, that are provided in a manner accessible
    via the exec family of functions".

    https://pubs.opengroup.org/onlinepubs/9699919799/functions/confstr.html

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