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Andrés Muñoz
Asked: 2020-02-11 17:21:04 +0800 CST 2020-02-11 17:21:04 +0800 CST

What is the difference between #!/usr/bin/python and #!/usr/bin/env python?

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I have seen that many times these lines are used #!/usr/bin/pythonand #!/usr/bin/env pythonat the beginning of the scripts and I was wondering if there was any difference, if there is, which one is more recommended to use?

python

1 Answers

  1. Best Answer

    #!/usr/bin/env python

    I would say that this is the most recommended as it makes use of the environment to look for the first occurrence of the Python executable. If you read the documentation for the command env:

    $ man env
ENV(1)

NAME
       env - run a program in a modified environment
...

    It is understood that you execute a command in a modified environment. Let's see what's in it $PATH:

    $ env
...
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/home/cesar/Development/Android/android-sdk-linux/platform_tools:/home/cesar/Development/Android/android-sdk-linux/tools
...

    Then when using it #!/usr/bin/env pythonwill search for the executable of the command pythonaccording to the paths defined in $PATHyour environment, this is good since it is possible that you have several versions of Python installed (in Linux you usually have version 2 and 3).

    If we try this in the terminal (result may vary):

    $ env python
Python 2.7.6 (default, Jun 22 2015, 18:00:18) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>

    To demonstrate the operation of envwe are going to do some tests. We create a symbolic link from python3a /usr/local/bin:

    $ sudo ln -s /usr/bin/python3 /usr/local/bin/python

    You can notice above that in my $PATH, the path /usr/local/binis before the path /usr/binso if I run again:

    $ env python
Python 3.4.3 (default, Oct 14 2015, 20:33:09) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

    Now I get version 3 of Python. Observe what happens if I modify the $PATHfor test purposes:

    • With /usr/binas first route:

      $ PATH="/usr/bin/:/usr/local/bin"
$ env python
Python 2.7.6 (default, Jun 22 2015, 18:00:18) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>

    • With /usr/local/binas first route:

      $ PATH="/usr/local/bin:/usr/bin"
$ env python
Python 3.4.3 (default, Oct 14 2015, 20:33:09) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

    I hope this is clear, I think it is an advantage to use this way but sometimes it may not work as you expect if the Python paths have been manipulated, although it is also possible to be a bit more specific and use for example one of these in your script:

    • #!/usr/bin/env python2
    • #!/usr/bin/env python3

    #!/usr/bin/python

    This is also valid, you are simply calling the path of the Python executable:

    $ which python
/usr/bin/python

    I have run into some problems with this way, I seem to remember that in some Linux distributions the Python executable was not found in the /usr/bin/python.

    final notes

    • The use of characters at the beginning of scripts is known as shebang .#!
    • The shebang is recognized on Unix-like systems (Linux, Mac), on Windows it is simply ignored
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