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    <pre><code>#!/usr/bin/env python """Start process; wait 2 seconds; kill the process; print all process output.""" import subprocess import tempfile import time def main(): # open temporary file (it automatically deleted when it is closed) # `Popen` requires `f.fileno()` so `SpooledTemporaryFile` adds nothing here f = tempfile.TemporaryFile() # start process, redirect stdout p = subprocess.Popen(["top"], stdout=f) # wait 2 seconds time.sleep(2) # kill process #NOTE: if it doesn't kill the process then `p.wait()` blocks forever p.terminate() p.wait() # wait for the process to terminate otherwise the output is garbled # print saved output f.seek(0) # rewind to the beginning of the file print f.read(), f.close() if __name__=="__main__": main() </code></pre> <h1>Tail-like Solutions that print only the portion of the output</h1> <p>You could read the process output in another thread and save the required number of the last lines in a queue:</p> <pre><code>import collections import subprocess import time import threading def read_output(process, append): for line in iter(process.stdout.readline, ""): append(line) def main(): # start process, redirect stdout process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True) try: # save last `number_of_lines` lines of the process output number_of_lines = 200 q = collections.deque(maxlen=number_of_lines) # atomic .append() t = threading.Thread(target=read_output, args=(process, q.append)) t.daemon = True t.start() # time.sleep(2) finally: process.terminate() #NOTE: it doesn't ensure the process termination # print saved lines print ''.join(q) if __name__=="__main__": main() </code></pre> <p>This variant requires <code>q.append()</code> to be atomic operation. Otherwise the output might be corrupted.</p> <h2><a href="http://docs.python.org/library/signal.html#signal.alarm" rel="noreferrer"><code>signal.alarm()</code></a> solution</h2> <p>You could use <a href="http://docs.python.org/library/signal.html#signal.alarm" rel="noreferrer"><code>signal.alarm()</code></a> to call the <code>process.terminate()</code> after specified timeout instead of reading in another thread. Though it might not interact very well with the <code>subprocess</code> module. Based on <a href="https://stackoverflow.com/questions/1191374/subprocess-with-timeout/1191537#1191537">@Alex Martelli's answer</a>:</p> <pre><code>import collections import signal import subprocess class Alarm(Exception): pass def alarm_handler(signum, frame): raise Alarm def main(): # start process, redirect stdout process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True) # set signal handler signal.signal(signal.SIGALRM, alarm_handler) signal.alarm(2) # produce SIGALRM in 2 seconds try: # save last `number_of_lines` lines of the process output number_of_lines = 200 q = collections.deque(maxlen=number_of_lines) for line in iter(process.stdout.readline, ""): q.append(line) signal.alarm(0) # cancel alarm except Alarm: process.terminate() finally: # print saved lines print ''.join(q) if __name__=="__main__": main() </code></pre> <p>This approach works only on *nix systems. It might block if <code>process.stdout.readline()</code> doesn't return.</p> <h2><a href="http://docs.python.org/library/threading.html#threading.Timer" rel="noreferrer"><code>threading.Timer</code></a> solution</h2> <pre><code>import collections import subprocess import threading def main(): # start process, redirect stdout process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True) # terminate process in timeout seconds timeout = 2 # seconds timer = threading.Timer(timeout, process.terminate) timer.start() # save last `number_of_lines` lines of the process output number_of_lines = 200 q = collections.deque(process.stdout, maxlen=number_of_lines) timer.cancel() # print saved lines print ''.join(q), if __name__=="__main__": main() </code></pre> <p>This approach should also work on Windows. Here I've used <code>process.stdout</code> as an iterable; it might introduce an additional output buffering, you could switch to the <code>iter(process.stdout.readline, "")</code> approach if it is not desirable. if the process doesn't terminate on <code>process.terminate()</code> then the scripts hangs.</p> <h2>No threads, no signals solution</h2> <pre><code>import collections import subprocess import sys import time def main(): args = sys.argv[1:] if not args: args = ['top'] # start process, redirect stdout process = subprocess.Popen(args, stdout=subprocess.PIPE, close_fds=True) # save last `number_of_lines` lines of the process output number_of_lines = 200 q = collections.deque(maxlen=number_of_lines) timeout = 2 # seconds now = start = time.time() while (now - start) &lt; timeout: line = process.stdout.readline() if not line: break q.append(line) now = time.time() else: # on timeout process.terminate() # print saved lines print ''.join(q), if __name__=="__main__": main() </code></pre> <p>This variant use neither threads, no signals but it produces garbled output in the terminal. It will block if <code>process.stdout.readline()</code> blocks.</p>
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