Question

I’m trying to get a few filenames by executing this command in os.popen :

ls /etc/tor/statistiekjes/ |egrep dns

But when I run my script I get :

<open file 'ls /etc/tor/statistiekjes/ |egrep dns', mode 'r' at 0xb7786860>
egrep: write error: Broken pipe

Code :

lscmd = "ls /etc/tor/statistiekjes/ |egrep "+FILE
print lscmd
inputList=os.popen(lscmd,'r')

File is an argument past to the script to grep on

Answer 1

For this particular problem, you could use native Python calls:

import os
import re
for name in (name for name in  os.listdir('/etc/tor/statistiekjes/')
             if re.search(FILE,name)):
    print(repr(name))

However, you are probably looking for a more general solution to calling external programs. In that case, use subprocess instead of os.popen, since os.popen is deprecated:

import subprocess
import shlex
proc1 = subprocess.Popen(shlex.split('ls /etc/tor/statistiekjes/'),
                         stdout=subprocess.PIPE)
proc2 = subprocess.Popen(shlex.split('egrep {pat}'.format(pat=FILE)),
                         stdin=proc1.stdout,
                         stdout=subprocess.PIPE,stderr=subprocess.PIPE)

proc1.stdout.close() # Allow proc1 to receive a SIGPIPE if proc2 exits.
out,err=proc2.communicate()
print(out)

See “Replacing shell pipeline”.

PS. subprocess.Popen has a shell=True parameter which could also be used. However, it is best to avoid using shell=True if possible. It is a security risk.