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Anyone know this? I've never been able to find an answer.

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    not a ton. i'm on osx and the env manpage is rather ambiguous there. Commented Aug 30, 2009 at 2:37
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    @S.Lott: Have you read it lately? On my Debian box, it's one of the most unhelpful man pages I've ever seen, and that's saying something. (Here's the whole "Description": Set each NAME to VALUE in the environment and run COMMAND. Yup, that would clear him right up.) Commented Aug 30, 2009 at 2:42
  • @Telemachus: Yes, I did read it. It's why I found the Wikipedia entry. Commented Aug 30, 2009 at 2:44
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    One problem with env is that you can't add -u or any other option to be passed to the python executable Commented Aug 30, 2009 at 2:56
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    Also a very good answer on a very related Unix SE question is here. Commented Nov 28, 2012 at 0:46

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If you're prone to installing python in various and interesting places on your PATH (as in $PATH in typical Unix shells, %PATH on typical Windows ones), using /usr/bin/env will accomodate your whim (well, in Unix-like environments at least) while going directly to /usr/bin/python won't. But losing control of what version of Python your scripts run under is no unalloyed bargain... if you look at my code you're more likely to see it start with, e.g., #!/usr/local/bin/python2.5 rather than with an open and accepting #!/usr/bin/env python -- assuming the script is important I like to ensure it's run with the specific version I have tested and developed it with, NOT a semi-random one;-).

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Of course, you can always use #!/usr/bin/env python2.5 to constrain the set of semi-random choices :=)
+1 Great explanation, thanks! I hadn't come across that usage of "env" before...now I have something to add to my scripting bag-of-tricks.
+1 for justification of NOT using "env python". Made me realize that if I want to use "env python", I'd better be coding for the lowest common denominator, since I'd have no control over the version of python the user has first in the PATH.
-1 for several reasons: /usr/local/bin is not a standard path for python, would work only for locally compiled installs; Enforcing minor version at shebang a bad idea: may protect from 2.4, but it also claims your script is incompatible with, say, 2.6 or 2.7. Minor version restrain is a task for distutils/setup.py, package management system, or conditional imports, not shebang; Also, as @Ned said, you should not hardcode paths or prevent user for having his python 2.5 in ~/bin if the system does not provide one. So, bad future-proof and abysmal portability.
Be aware also of the fact that using #!/usr/bin/env python and virtualenvs will execute the script in current venv! This may or may not be a good thing, depends on your use case.
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From wikipedia

Shebangs specify absolute paths to system executables; this can cause problems on systems which have non-standard file system layouts

Often, the program /usr/bin/env can be used to circumvent this limitation

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it finds the python executable in your environment and uses that. it's more portable because python may not always be in /usr/bin/python. env is always located in /usr/bin.

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env is not always there, but we are increasing the probability of the script finding python on more machines. :)
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It finds 'python' also in /usr/local/bin, ~/bin, /opt/bin, ... or wherever it may hide.

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thanks! it actually caused a problem for me because, for some reason, env didn't' exist.
That's a bit misleading. It's only going to find the first "python" on your current $PATH and Python instances on OS X can be pretty good at hiding. In particular, the standard framework builds from python.org and others have "bin" subdirectories within the framework where "python" and other executables and scripts are stored. It's very easy to end up with multiple instances which may or may not have symlinks to them in the usual places, like /usr/local/bin et al. Managing $PATH on OS X in this case is not as straightforward as on systems without framework-style builds.
@KennethReitz: if /usr/bin/env does not exist, your system is broken. envis a required tool by POSIX standard.
@MestreLion, POSIX is not a requirement for running python.
@KennethReitz: true, but shebangs are used only in POSIX environments. Windows (and python) ignores them, so I assumed you were on *nix environment, otherwise your original question is moot.
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You may find this post to be of interest: http://mail.python.org/pipermail/python-list/2008-May/661514.html

This may be a better explanation: http://mail.python.org/pipermail/tutor/2007-June/054816.html

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