how to execute a bash command in a python script

Question

How can I launch a bash command with multiple args (for example "sudo apt update") from a python script?

Solution 1

@milne's answer works, but subprocess.call() gives you little feedback.

I prefer to use subprocess.check_output() so you can analyse what was printed to stdout:

 import subprocess
 res = subprocess.check_output(["sudo", "apt", "update"])
 for line in res.splitlines():
     # process the output line by line

check_output throws an error on on-zero exit of the invoked command

Please note that this doesn't invoke bash or another shell if you don't specify the shell keyword argument to the function (the same is true for subprocess.call(), and you shouldn't if not necessary as it imposes a security hazard), it directly invokes the command.

If you find yourself doing a lot of (different) command invocations from Python, you might want to look at plumbum. With that you can do the (IMO) more readable:

from plumbum.cmd import sudo, apt, echo, cut

res = sudo[apt["update"]]()
chain = echo["hello"] | cut["-c", "2-"]
chain()

Solution 2

It is possible you use the bash as a program, with the parameter -c for execute the commands:

Example:

bashCommand = "sudo apt update"
output = subprocess.check_output(['bash','-c', bashCommand])

Solution 3

The subprocess module is designed to do this:

import subprocess
subprocess.call(["sudo", "apt", "update"])

If you would like the script to terminate if the command fails, you might consider using check_call() instead of parsing the return code yourself:

subprocess.check_call(["sudo", "apt", "update"])

Solution 4

Also you can use 'os.popen'.

Example:

import os

command = os.popen('ls -al')
print(command.read())
print(command.close())

Output:

total 16
drwxr-xr-x 2 root root 4096 ago 13 21:53 .
drwxr-xr-x 4 root root 4096 ago 13 01:50 ..
-rw-r--r-- 1 root root 1278 ago 13 21:12 bot.py
-rw-r--r-- 1 root root   77 ago 13 21:53 test.py

None

Solution 5

For python 3.5 and more you can use:

import subprocess

try:        
    result = subprocess.run("sudo apt update", check=True, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
except subprocess.CalledProcessError as err:
    raise Exception(str(err.stderr.decode("utf-8")))
except Exception as err:
    raise Exception(err)
else:
    return result.stdout.decode("utf-8")

View more solutions

Comments

[don_crissti]

docs.python.org/3/library/subprocess.html

[Dremor]

this gave me the following traceback : Traceback (most recent call last): File "/home/Dremor/test.py", line 3, in <module> subprocess.call('sudo', 'yum', 'update') File "/usr/lib64/python3.4/subprocess.py", line 537, in call with Popen(*popenargs, **kwargs) as p: File "/usr/lib64/python3.4/subprocess.py", line 767, in __init__ raise TypeError("bufsize must be an integer") TypeError: bufsize must be an integer (I'm using yum as I'm using Fedora as main OS)

[Milind Dumbare]

You forgot the square brackets

[heemayl]

Also note that subprocess.call() is blocking while subprocess.Popen() is non-blocking..

[alper]

Is it recommended to use (os.popen or os.system), ex: res = os.popen('sudo apt update').read()? @Anthon

[alper]

I am using long complicated shell commands, hence using under os.system() is pretty easy, where I just need to give command line as input string. Why is it not recommend to be used? @Anthon

[Anthon]

It starts an extra shell just to execute the command, you don't get any feedback from os.system().

[alper]

How about following example: os.popen('my_command').read() which returns an output. But as I understand extra shell consumes additional time. @Anthob

[Anthon]

@alper Read 0324 python.org/dev/peps/pep-0324. That explains the rationale for making subprocess although os.system and os.popen already existed. Such PEPs are non-trivial to get accepted. Several people have given much more thought to that than you or I ever will. And subprocess has improved since 2003, the others are just still there for backward compatibility. Have you red the os.system manual page: The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function.

[alper]

Could I use as with shell=True option is it recommended way to use, example: subprocess.check_output('sudo apt update', shell=True).strip().decode('utf-8') @Anthon

[Anthon]

@alper Yes you could. As I indicated that is a potential security hazard, so I don't know why you think that is recommended. And invoking sudo is only going to make that more severe. Maybe using python-apt is a better solution (I have not looked into that myself).

[alper]

I will use it without providing sudo for general commands. I have to use | (pipe) on my commands, which I cannot able to use it via subprocess.run(). For example command(echo hello | cut -c 2-) => res = subprocess.check_output(["echo", "hello", "|", "cut -c 2-"]) does not see |. If you could extend your answer for pipe | usage under subprocess that will be so helpful.

[Anthon]

@alper in that case take a serious look at plumbum, it is worth getting up to speed with that.

[alper]

subprocess.check_output() returns byte stream (b''), I guess we need to add .decode('utf-8').strip() to end of subprocess.check_output(["sudo", "apt", "update"]) to convert it into character stream. Instead of doing this additional conversion, could we use subprocess.Popen with universal_newlines=True flag: res = subprocess.Popen(['sudo', 'apt', 'update'], stdout=subprocess.PIPE, universal_newlines=True).communicate()[0].strip() to increase its speed?

[Anthon]

@alper If you are on Python3 you need to do that, on Python2 you don't. Please don't use the commenting here as a chat system. If you have a question post it as such.

[alper]

What do you mean by "blocking"? @heemayl

[aquagremlin]

why am i getting an error when i use it

[aquagremlin]

subprocess.check_call(["sudo", "apt", "update"])

[aquagremlin]

CalledProcessError Traceback (most recent call last) <ipython-input-21-33ce645708e7> in <module>() ----> 1 subprocess.check_call(["sudo", "apt", "update"]) /usr/lib/python2.7/subprocess.pyc in check_call(*popenargs, **kwargs) 188 if cmd is None: 189 cmd = popenargs[0] --> 190 raise CalledProcessError(retcode, cmd) 191 return 0 192 CalledProcessError: Command '['sudo', 'apt', 'update']' returned non-zero exit status 1

[aquagremlin]

this error only happens when i run it in a jupyter notebook

[aquagremlin]

maybe i'll start a new question since this is ot