Python subprocess.Popen() error (No such file or d

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

Answer 1

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"]

Answer 2

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.