[Rob Wolfe]
| Hari Sekhon wrote:
| > I am writing a wrapper to a binary command to run it and then do
| > something with the xml output from it.
| >
| > What is the best way of making sure that the command is
| installed on the
| > system before I try to execute it, like the python equivalent of the
| > unix command "which"?
| >
| > Otherwise I'd have to do something like:
| >
| > if os.system('which somecommand') != 0:
| > print "you don't have %s installed" % somecommand
| > sys.exit(1)
| >
| > I know that isn't portable which is why a python solution would be
| > better (although this will run on unix anyway, but it'd be
| nice if it
| > ran on windows too).
|
| IMHO this is pretty portable:
|
| >>> def is_on_path(fname):
| ... for p in os.environ['PATH'].split(os.pathsep):
| ... if os.path.isfile(os.path.join(p, fname)):
| ... return True
| ... return False
|
Depends on how "fname" is specified: on Win32, the filename
itself will have one of the PATHEXT extensions, even though you
conventionally don't specify it (and if you're after
portability you certainly won't). On *nix, tho', you almost
certainly won't have the extension.
As it happens I wrote a script similar to yours this morning
which takes account of the PATHEXT, but because of that, it's
obviously win-specific. Maybe it could be made a bit smarter
to account for the possible absence of the env var.
(This is a cut-down version)
<code>
import os, sys
class x_finished (Exception): pass
paths = ["."] + os.environ.get ("PATH", "").split (";")
exts = [e.lower () for e in os.environ.get ("PATHEXT", ".exe").split
(";")]
if __name__ == '__main__':
if len (sys.argv) > 1:
search_for = sys.argv[1]
else:
search_for = raw_input ("Search for:")
base, ext = os.path.splitext (search_for)
if ext:
exts = [ext]
try:
for path in paths:
for ext in exts:
filepath = os.path.join (path, "%s%s" % (base, ext))
if os.path.isfile (filepath):
print filepath
raise x_finished
except x_finished:
pass
</code>
TJG
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