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Running shell command from Python and capturing the output

I want 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'

Answer

**I had a slightly different flavor of the same problem with the following requirements:**

1. Capture and return STDOUT messages as they accumulate in the STDOUT buffer (i.e. in realtime). 
   - *@vartec solved this Pythonically with his use of generators and the 'yield'  
    keyword above*
2. Print all STDOUT lines (*even if process exits before STDOUT buffer can be fully read*)
2. Don't waste CPU cycles polling the process at high-frequency
2. Check the return code of the subprocess
3. Print STDERR (separate from STDOUT) if we get a non-zero error return code.

**I've combined and tweaked previous answers to come up with the following:**

def run_command(command):
        p = subprocess.Popen(command,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE,
                             shell=True)
        # Read stdout from subprocess until the buffer is empty !
        for line in iter(p.stdout.readline, b''):
            if line: # Don't print blank lines
                yield line
        # This ensures the process has completed, AND sets the 'returncode' attr
        while p.poll() is None:                                                                                                                                        
            sleep(.1) #Don't waste CPU-cycles
        # Empty STDERR buffer
        err = p.stderr.read()
        if p.returncode != 0:
           # The run_command() function is responsible for logging STDERR 
           print "Error: " + err

**This code would be executed the same as previous answers:**

for line in run_command(cmd):
        print line

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Running shell command from Python and capturing the output

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