Running shell command and capturing the output

0 votes

How to write a function that will execute a shell command and return its output as a string, no matter, is it an error or success message. I just want to get the same result that I would have gotten with the command line.

What would be a code example that would do such a thing?

For example:

def run_command(cmd):
    # ??????

print run_command('mysqladmin create test -uroot -pmysqladmin12')
# Should output something like:
# mysqladmin: CREATE DATABASE failed; error: 'Can't create database 'test'; database exists'
Dec 28, 2020 in Python by anonymous
• 10,520 points
2,864 views

1 answer to this question.

0 votes

Modern versions of Python (3.5 or higher): run

If you're using Python 3.5+, and do not need backwards compatibility, the new run function is recommended by the official documentation for most tasks. It provides a very general, high-level API for the subprocess module. To capture the output of a program, pass the subprocess.PIPE flag to the stdout keyword argument. Then access the stdout attribute of the returned CompletedProcess object:

>>> import subprocess
>>> result = subprocess.run(['ls', '-l'], stdout=subprocess.PIPE)
>>> result.stdout
b'total 0\n-rw-r--r--  1 memyself  staff  0 Mar 14 11:04 files\n'

The return value is a bytes object, so if you want a proper string, you'll need to decode it. Assuming the called process returns a UTF-8-encoded string:

>>> result.stdout.decode('utf-8')
'total 0\n-rw-r--r--  1 memyself  staff  0 Mar 14 11:04 files\n'

This can all be compressed to a one-liner if desired:

>>> subprocess.run(['ls', '-l'], stdout=subprocess.PIPE).stdout.decode('utf-8')
'total 0\n-rw-r--r--  1 memyself  staff  0 Mar 14 11:04 files\n'

If you want to pass input to the process's stdin, you can pass a bytes object to the input keyword argument:

>>> cmd = ['awk', 'length($0) > 5']
>>> ip = 'foo\nfoofoo\n'.encode('utf-8')
>>> result = subprocess.run(cmd, stdout=subprocess.PIPE, input=ip)
>>> result.stdout.decode('utf-8')
'foofoo\n'

You can capture errors bypassing stderr=subprocess.PIPE (capture to result.stderr) or stderr=subprocess.STDOUT (capture to result.stdout along with regular output). If you want to be run to throw an exception when the process returns a nonzero exit code, you can pass check=True. (Or you can check the return code attribute of the result above.) When security is not a concern, you can also run more complex shell commands by passing shell=True as described at the end of this answer.

Later versions of Python streamline the above further. In Python 3.7+, the above one-liner can be spelled like this:

>>> subprocess.run(['ls', '-l'], capture_output=True, text=True).stdout
'total 0\n-rw-r--r--  1 memyself  staff  0 Mar 14 11:04 files\n'

Using run this way adds just a bit of complexity, compared to the old way of doing things. But now you can do almost anything you need to do with the run function alone.

Get output from shell command using subprocess

Launch the shell command that we want to execute using subprocess. Popen function. The arguments to this command is the shell command as a list and specify output and error. The output from subprocess.

To capture the output of the subprocessrun method, use an additional argument named “capture_output=True”. You can individually access stdout and stderr values by using “outputstdout” and “output.

answered Dec 28, 2020 by Gitika
• 65,890 points

Related Questions In Python

0 votes
1 answer

What is the output of and explanation?

It will print concatenated lists. Output would ...READ MORE

answered Jul 20, 2018 in Python by Priyaj
• 58,100 points
805 views
+1 vote
0 answers

Sum the values of column matching and not matching from a .txt file and write output to a two different files using Python

Name                                                    value DR_CNDAOFSZAPZP_GPFS_VOL.0 139264 DR_CNDAOFSZAPZP_GPFS_VOL.1 15657 DR_CNDAOFSZAPZP_GPFS_VOL.0 139264 DR_CNDAOFSZAPZP_GPFS_VOL.1 156579 DR_CNDAOFSZAPZP_GPFS_VOL.2 156579 DR_CNDAOFSZAPZP_GPFS_VOL.3 ...READ MORE

Nov 20, 2019 in Python by Sagar
• 130 points
1,138 views
0 votes
1 answer

Restart python script automatically even when it crashes in Linux

Maybe this would be more robust? 1) save ...READ MORE

answered Sep 11, 2018 in Python by Priyaj
• 58,100 points
2,999 views
0 votes
1 answer

Restart python script automatically even when it crashes in Linux

Maybe this would be more robust? 1) save ...READ MORE

answered Sep 21, 2018 in Python by Priyaj
• 58,100 points
3,972 views
0 votes
1 answer

External command in Python

you can check the subprocess module in ...READ MORE

answered Oct 1, 2018 in Python by SDeb
• 13,300 points
623 views
0 votes
1 answer
0 votes
1 answer

What will be the output of below code and why? x=[1,2,3,4,5] print(x.insert(2,3))

If you write x.insert(2,3) and then print x ...READ MORE

answered Oct 14, 2020 in Python by Gitika
• 65,890 points
4,231 views
0 votes
1 answer

why is the dcount and tcount 0 and 0 in the output?

Because the dcount and tcount variables you ...READ MORE

answered Nov 6, 2020 in Python by Gitika
• 65,890 points
646 views
webinar REGISTER FOR FREE WEBINAR X
REGISTER NOW
webinar_success Thank you for registering Join Edureka Meetup community for 100+ Free Webinars each month JOIN MEETUP GROUP