How to store the result of an executed shell command in a variable in python?

Question

I need to store the result of a shell command that I executed in a variable, but I couldn't get it working. I tried like:

import os    

call = os.system("cat syscall_list.txt | grep f89e7000 | awk '{print $2}'")
print call

But it prints the result in terminal and prints the value of call as zero, possibly indicating as success. How to get the result stored in a variable?

Solution 1

Use the subprocess module instead:

import subprocess
output = subprocess.check_output("cat syscall_list.txt | grep f89e7000 | awk '{print $2}'", shell=True)

Edit: this is new in Python 2.7. In earlier versions this should work (with the command rewritten as shown below):

import subprocess
output = subprocess.Popen(['awk', '/f89e7000/ {print $2}', 'syscall_list.txt'], stdout=subprocess.PIPE).communicate()[0]

---

As a side note, you can rewrite

cat syscall_list.txt | grep f89e7000

To

grep f89e7000 syscall_list.txt

And you can even replace the entire statement with a single awk script:

awk '/f89e7000/ {print $2}' syscall_list.txt

Leading to:

import subprocess
output = subprocess.check_output(['awk', '/f89e7000/ {print $2}', 'syscall_list.txt'])

Solution 2

os.popen works for this. popen - opens a pipe to or from command. The return value is an open file object connected to the pipe, which can be read. split('\n') converts the output to list

import os
list_of_ls = os.popen("ls").read().split('\n')
print list_of_ls

import os
list_of_call = os.popen("cat syscall_list.txt | grep f89e7000 | awk '{print $2}'").read().split('\n')
print list_of_call

Solution 3

commands.getstatusoutput would work well for this situation. (Deprecated since Python 2.6)

import commands
print(commands.getstatusoutput("cat syscall_list.txt | grep f89e7000 | awk '{print $2}'"))

Solution 4

In python 3 you can use

import subprocess as sp
output = sp.getoutput('whoami --version')
print (output)

``

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Comments

[georg]

see here: stackoverflow.com/questions/1410976/…

[user567879]

I am using python 2.6.6 and it gives me error: AttributeError: 'module' object has no attribute 'check_output'

[Rob Wouters]

@user567879, You are right. This function was added in Python 2.7. I'll edit in a method for Python 2.6.

[user567879]

What if i need to pass a python variable as an argument to the executed shell command?

[Rob Wouters]

@user567879: Just do it how you would normally put a variable in a list, i.e. ['awk', '/f89e7000/ {print $2}', filename], and pass that to Popen().

[user3885927]

The link doesn't work any more and this is removed in 3.x See docs.python.org/2/library/commands.html