Python: Check existence of shell command before execution
Solution 1
You can use the subprocess module under Python 3 or the commands module for Python 2 as follow :
status, result = subprocess.getstatusoutput("ls -al")
status, result = commands.getstatusoutput("ls -al")
Then test the value of status
.
Examples from the website :
>>> import subprocess >>> subprocess.getstatusoutput('ls /bin/ls') (0, '/bin/ls') >>> subprocess.getstatusoutput('cat /bin/junk') (256, 'cat: /bin/junk: No such file or directory') >>> subprocess.getstatusoutput('/bin/junk') (256, 'sh: /bin/junk: not found')
Solution 2
couldn't you use the "which" command somehow? the which command automatically performs a lookup for an application in the paths. I think you would merely need to call this command and pass the name of the command you want to look up, then parse the results.
Solution 3
For situations like this, I use:
def find_program(prog_filename, error_on_missing=False):
bdirs = ['$HOME/Environment/local/bin/',
'$HOME/bin/',
'/share/apps/bin/',
'/usr/local/bin/',
'/usr/bin/']
paths_tried = []
for d in bdirs:
p = os.path.expandvars(os.path.join(d, prog_filename))
paths_tried.append(p)
if os.path.exists(p):
return p
if error_on_missing:
raise Exception("*** ERROR: '%s' not found on:\n %s\n" % (prog_filename, "\n ".join(paths_tried)))
else:
return None
Then you can do something like:
grep_path = find_program('ack_grep', False)
if grep_path is None:
# default to standard system grep
grep_path = 'grep'
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Gabriel L. Oliveira
Updated on September 17, 2022Comments
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Gabriel L. Oliveira over 1 year
I'm trying to find a way to check the existence of a shell command before its execution.
For example, I'll execute the command ack-grep. So, I'm trying to do:
import subprocess
from subprocess import PIPE
cmd_grep = subprocess.Popen(["ack-grep", "--no-color", "--max-count=1", "--no-group", "def run_main", "../cgedit/"], stdout=PIPE, stderr=PIPE)Than, if I execute
cmd_grep.stderr.read()
I receive '' like the output. But I don't have the command ack-grep on my path. So, why Popen is not putting the error message on my .stderr variable?
Also, is there a easyer way to do what I'm trying to do?
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trolle3000 almost 14 yearsYou should probably ask this on stackoverflow
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Scott - Слава Україні over 5 yearsThis would be a better answer if you (1) used a more plausible (useful) example of commands, like the OP’s example of
ack-grep
versusgrep
, and (2) showed the code for using the command you want to use versus using the fallback.