shebang strange thing...

Michael Coleman mkc at stowers-institute.org
Thu Jun 26 00:34:43 CEST 2003


brian_l at yahoo.com (Brian Lenihan) writes:
> If you have two or more Python installations, the first one in
> your path gets invoked no matter what the shebang line says.
> 
> If the first line of a script is #!/usr/local/bin/python, I expect the
> interpreter located in /usr/local/bin to execute the script, not the
> one in /usr/bin, or the one in /sw/bin, but that is what you get if
> you run the script as an executable.
> 
> The process list shows why - python is called without a path, e.g. as
> "python".  The same behavior occurs if the shell is bash or tcsh.
> As far as I know, OS X is the only "modern" Unix to behave this way.

Tru64 (5.1) also shows this behavior (which recently bit me too), but
it's arguably a bug in Python rather than in the OS.  If you look
carefully, I think you'll find that the correct binary (e.g.,
/usr/local/bin/python) is in fact being invoked, but that that binary
then uses the libraries associated with the first python in your PATH.
The reason this is happening is that python determines where all of
its libraries live by examining argv[0], if a more suitable method is
not available.  If this gives the full path, everything is fine, but
if only the basename is given ("python"), then the startup code walks
to the PATH to guess.  As you've noticed, in some cases, this guess is
wrong.

Mike

-- 
Mike Coleman, Scientific Programmer, +1 816 926 4419
Stowers Institute for Biomedical Research
1000 E. 50th St., Kansas City, MO  64110




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