[Python-bugs-list] [ python-Bugs-601077 ] bug in new execvpe

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Bugs item #601077, was opened at 2002-08-27 21:03
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=601077&group_id=5470

Category: Python Library
Group: Python 2.2
Status: Open
Resolution: None
Priority: 5
Submitted By: Guido van Rossum (gvanrossum)
Assigned to: Nobody/Anonymous (nobody)
Summary: bug in new execvpe

Initial Comment:
From: "Steve M. Robbins" <steven.robbins@videotron.ca>


I think the patch associated with this thread has an
unintended
consequence.

In
http://mail.python.org/pipermail/python-dev/2002-August/027229.html
Zack pointed out three flaws in the original code:

    [...]
    Third, if an error other than the expected one
comes back, the
    loop clobbers the saved exception info and keeps
going.  Consider
    the situation where PATH=/bin:/usr/bin, /bin/foobar
exists but is
    not executable by the invoking user, and
/usr/bin/foobar does not
    exist.  The exception thrown will be 'No such file
or directory',
    not the expected 'Permission denied'.

The patch, as I understand it, changes the behaviour so
as to raise
the exception "Permission denied" in this case.

Consider a similar situation in which both /bin/foobar
(not executable
by the user) and /usr/bin/foobar (executable by the
user) exist.
Given the command "foobar", the shell will execute
/usr/bin/foobar.
If I understand the patch correctly, python will give
up when it
encounters /bin/foobar and raise the "Permission
denied" exception.

I believe this just happened to me today.  I had a
shell script named
"gcc" in ~/bin (first on my path) some months back. 
When I was
finished with it, I just did "chmod -x ~/bin/gcc" and
forgot about it.
Today was the first time since this patch went in that
I ran gcc via
python (using scipy's weave).  Boy was I surprised at
the message
"unable to execute gcc: Permission denied"!

I guess the fix is to save the EPERM exception and keep
going
in case there is an executable later in the path.


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