subprocess.Popen() error (No such file or directory) when calling command with arguments as a string

Question

I am trying to count the number of lines in a file using Python functions. Within the current directory, while os.system("ls") finds the file, the command subprocess.Popen(["wc -l filename"], stdout=subprocess.PIPE) does not work.

Here is my code:

>>> import os >>> import subprocess >>> os.system("ls") sorted_list.dat 0 >>> p = subprocess.Popen(["wc -l sorted_list.dat"], stdout=subprocess.PIPE)File "<stdin>", line 1, in <module> File "/Users/a200/anaconda/lib/python2.7/subprocess.py", line 710, in __init__ errread, errwrite) File "/Users/a200/anaconda/lib/python2.7/subprocess.py", line 1335, in _execute_child raise child_exception OSError: [Errno 2] No such file or directory

bakkal · Accepted Answer · 2023-09-05 11:32:53Z

You should pass the arguments as a list (recommended):

subprocess.Popen(["wc", "-l", "sorted_list.dat"], stdout=subprocess.PIPE)

Otherwise, you need to pass shell=True if you want to use the whole "wc -l sorted_list.dat" string as a command (not recommended, can be a security hazard).

subprocess.Popen("wc -l sorted_list.dat", shell=True, stdout=subprocess.PIPE)

Read more about shell=True security issues here.

In this case, to use the command as a whole string and avoid the security issues of shell=True you can use shlex

import subprocess import shlex command = "wc -l sorted_list.dat" subprocess.Popen(shlex.split(command), stdout=subprocess.PIPE)

I am getting error : "python3: can't open file '$SDE/install/lib/python3.6/site-packages/p4testutils/bf_switchd_dev_status.py': [Errno 2] No such file or directory" even if shell=True. The same script runs properly on shell but gives error when called by subprocess. What may be the issue?
@Nagmat Is $SDE an env var or really the folder name? I think you may have to expand the value of $SDE in your python string first?
it is an environmental variable. I resolved the issue by writing the long path.

Antti Haapala · Accepted Answer · 2017-01-23 14:50:20Z

The error occurs because you are trying to run a command named wc -l sorted_list.dat, that is, it is trying to find a file named like "/usr/bin/wc -l sorted dat".

Split your arguments:

["wc", "-l", "sorted_list.dat"]

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