How can I use this bash test construct in Python?

Question

I have a bash snippet I would like to port over to Python. It finds where SVN is located and whether it is executable.

SVN=`which svn 2>&1` 
if [[ ! -x $SVN ]]; then
    echo "A subversion binary could not be found ($SVN)"        
fi

Here is my current attempt in Python using the subprocess module:

SVN = Popen('which svn 2>&1', shell=True, stdout=PIPE).communicate()[0]
Popen("if [[ ! -x SVN ]]; then echo 'svn could not be found or executed'; fi", shell=True)

This does not work because while I do have the location of SVN saved in the local namespace of Python, I can't access it from Popen.

I also tried combining into one Popen object:

Popen("if [[ ! -x 'which svn 2>&1']]; then echo 'svn could not be found'; fi", shell=True)

But I get this error (and needless to say, looks very unwieldy)

/bin/sh: -c: line 0: syntax error near `;'
/bin/sh: -c: line 0: `if [[ ! -x 'which svn 2>&1']]; then echo 'svn could not be found'; fi'

Is there a Python version of the test construct "-x"? I think that would be ideal. Other workarounds would be appreciated as well.

Thanks

[this site](http://ubuntuforums.org/showthread.php?t=1457094) provides a snippet that looks like `commands.getoutput("if [ -x myfile ]\nthen echo true\nfi")`. However this is hardly "porting to Python" since you're still invoking Bash. — Kos, Mar 11 '13 at 07:14
`os.stat` can give you some information about a given file, such as its permissions, but I think you'd still need to build up a "executable for current user" test on top of that. — Kos, Mar 11 '13 at 07:16
can you store the bash command as a string first, so that you can concatenate it with variable SVN? then pass that to Popen()... — Jeff, Mar 11 '13 at 07:16
Found it, the 'executable for current user' can be done using [`os.access`](http://docs.python.org/2/library/os.html#os.access). — Kos, Mar 11 '13 at 07:19

score 4 · Answer 1 · edited May 23 '17 at 10:25

4

This is the simplest solution:

path_to_svn = shutil.which('svn')
is_executable = os.access(path_to_svn, os.X_OK)

shutil.which is new in Python 3.3; there's a polyfill in this answer. You could grab the path from Popen too if you really want, but that's not necessary.

And here are the docs for os.access.

edited May 23 '17 at 10:25

Community

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answered Mar 11 '13 at 07:27

Kos

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`os.access()` is redundant. `shutil.which()` already checks `X_OK` by default. – jfs Mar 13 '13 at 04:11

Jeff · Accepted Answer · 2013-03-11T07:37:34.167

1

SVN = Popen('which svn 2>&1', shell=True, stdout=PIPE).communicate()[0]
str="if [[ ! -x " + SVN + " ]]; then echo 'svn could not be found or executed'; fi"
Popen(str, shell=True)

edited Mar 11 '13 at 07:37

answered Mar 11 '13 at 07:22

Jeff

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That's extremely inefficient, it forks a lot, and leaves zombie processes around. – LtWorf Mar 11 '13 at 08:08

score 1 · Answer 3 · answered Mar 11 '13 at 07:35

1

There is no need to use which, you can already try to run svn without parameters and if it works it means it's there.

try:
    SVN = subprocess.Popen('svn')
    SVN.wait()
    print "svn exists"
except OSError:
    print "svn does not exist"

answered Mar 11 '13 at 07:35

LtWorf

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How can I use this bash test construct in Python?

3 Answers3