How to use `subprocess` command with pipes
PythonLinuxSubprocessPipePython Problem Overview
I want to use subprocess.check_output()
with ps -A | grep 'process_name'
.
I tried various solutions but so far nothing worked. Can someone guide me how to do it?
Python Solutions
Solution 1 - Python
To use a pipe with the subprocess
module, you have to pass shell=True
.
However, this isn't really advisable for various reasons, not least of which is security. Instead, create the ps
and grep
processes separately, and pipe the output from one into the other, like so:
ps = subprocess.Popen(('ps', '-A'), stdout=subprocess.PIPE)
output = subprocess.check_output(('grep', 'process_name'), stdin=ps.stdout)
ps.wait()
In your particular case, however, the simple solution is to call subprocess.check_output(('ps', '-A'))
and then str.find
on the output.
Solution 2 - Python
Or you can always use the communicate method on the subprocess objects.
cmd = "ps -A|grep 'process_name'"
ps = subprocess.Popen(cmd,shell=True,stdout=subprocess.PIPE,stderr=subprocess.STDOUT)
output = ps.communicate()[0]
print(output)
The communicate method returns a tuple of the standard output and the standard error.
Solution 3 - Python
See the documentation on setting up a pipeline using subprocess: http://docs.python.org/2/library/subprocess.html#replacing-shell-pipeline
I haven't tested the following code example but it should be roughly what you want:
query = "process_name"
ps_process = Popen(["ps", "-A"], stdout=PIPE)
grep_process = Popen(["grep", query], stdin=ps_process.stdout, stdout=PIPE)
ps_process.stdout.close() # Allow ps_process to receive a SIGPIPE if grep_process exits.
output = grep_process.communicate()[0]
Solution 4 - Python
Using subprocess.run
import subprocess
ps = subprocess.run(['ps', '-A'], check=True, capture_output=True)
processNames = subprocess.run(['grep', 'process_name'],
input=ps.stdout, capture_output=True)
print(processNames.stdout)
Solution 5 - Python
You can try the pipe functionality in sh.py:
import sh
print sh.grep(sh.ps("-ax"), "process_name")
Solution 6 - Python
Also, try to use 'pgrep'
command instead of 'ps -A | grep 'process_name'
Solution 7 - Python
JKALAVIS solution is good, however I would add an improvement to use shlex instead of SHELL=TRUE. below im grepping out Query times
#!/bin/python
import subprocess
import shlex
cmd = "dig @8.8.4.4 +notcp www.google.com|grep 'Query'"
ps = subprocess.Popen(cmd,shell=True,stdout=subprocess.PIPE,stderr=subprocess.STDOUT)
output = ps.communicate()[0]
print(output)
Solution 8 - Python
command = "ps -A | grep 'process_name'"
output = subprocess.check_output(["bash", "-c", command])
Solution 9 - Python
After Python 3.5 you can also use:
import subprocess
f = open('test.txt', 'w')
process = subprocess.run(['ls', '-la'], stdout=subprocess.PIPE, universal_newlines=True)
f.write(process.stdout)
f.close()
The execution of the command is blocking and the output will be in process.stdout.