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Python non-blocking reading from stdout and stderr of subprocess.popen process using os.pipe and select.select
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| #!/usr/bin/env python | |
| # File: log_exec.py | |
| # Author: McKay Davis | |
| # Date: Jun 23, 2014 | |
| # Non-blocking stdout and stderr read from a | |
| # Popen process | |
| import os | |
| import subprocess | |
| import select | |
| def log_exec(args, env = None, log = None): | |
| ''' | |
| execute command and log process stdout and stderr | |
| to file-object 'log' while simultaneously logging to stdout | |
| ''' | |
| exec_env = {} | |
| exec_env.update(os.environ) | |
| # copy the OS environment into our local environment | |
| if env is not None: | |
| exec_env.update(env) | |
| # create a pipe to receive stdout and stderr from process | |
| (pipe_r, pipe_w) = os.pipe() | |
| p = subprocess.Popen(args, | |
| shell = False, | |
| env = exec_env, | |
| stdout = pipe_w, | |
| stderr = pipe_w) | |
| # Loop while the process is executing | |
| while p.poll() is None: | |
| # Loop long as the selct mechanism indicates there | |
| # is data to be read from the buffer | |
| while len(select.select([pipe_r], [], [], 0)[0]) == 1: | |
| # Read up to a 1 KB chunk of data | |
| buf = os.read(pipe_r, 1024) | |
| # Stream data to our stdout's fd of 0 | |
| os.write(0, buf) | |
| if log is not None: | |
| log.write(buf) | |
| # cleanup | |
| os.close(pipe_r) | |
| os.close(pipe_w) | |
| # return the result of the process | |
| return p.returncode | |
| # Test by running 'log_exec.py log.txt <cmd>' | |
| if __name__ == "__main__": | |
| import sys | |
| log_exec(sys.argv[2:], log=open(sys.argv[1], "wb")) |
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