Killing a child process

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

My script uses the SoX package to play a (long) sound file.

exec 'play "/home/myname/soundfile.wav" &';

I need to be able to stop the sound before reaching the end of the sound file. The SoX documentation says:

...it can be terminated earlier by sending an interrupt signal to the process (usually by pressing the keyboard interrupt key which is normally Ctrl-C)...

I tried this code to generate a child process, play the sound in that process, and kill the child process after a few seconds:

my $pid = fork || exec 'play "/home/myname/soundfile.wav" &';
sleep 5;
kill $pid;
[download]

It doesn't work, of course. What am I doing wrong?

Comment on Killing a child process Select or Download Code

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Re: Killing a child process by ikegami (Patriarch) on Oct 03, 2017 at 07:36 UTC
You're not executing `play`; you're executing a shell that forks and executes `play` and immediately exits. You are sending the signal to the zombie shell instead of `play`. Replace `exec 'play "/home/myname/soundfile.wav" &';` [download] with `exec 'play', '/home/myname/soundfile.wav';` [download]	[reply] [d/l] [select]
Re^2: Killing a child process by Anonymous Monk on Oct 03, 2017 at 07:47 UTC
Changing the code in that way also doesn't work. `my $pid = fork \|\| exec 'play', '/home/myname/soundfile.wav'; sleep 5; kill $pid;` [download]	[reply] [d/l]
Re^3: Killing a child process by ikegami (Patriarch) on Oct 03, 2017 at 07:51 UTC
What's not working? What error did it return?	[reply]
Re^4: Killing a child process by Anonymous Monk on Oct 03, 2017 at 08:11 UTC
Re^5: Killing a child process by hippo (Archbishop) on Oct 03, 2017 at 08:20 UTC
Re: Killing a child process by haukex (Archbishop) on Oct 03, 2017 at 08:09 UTC
I need to be able to stop the sound before reaching the end of the sound file. SoX also has the `trim` operation: `$ play "/home/myname/soundfile.wav" trim 0 5` [download] Should play only the first 5 seconds of your file.	[reply] [d/l] [select]
Re^2: Killing a child process by Anonymous Monk on Oct 03, 2017 at 08:13 UTC
I checked the SoX documentation for stuff like that, but I need to stop the sound playback 'on demand'; I don't know in advance when the playback will be stopped.	[reply]
Re^3: Killing a child process by haukex (Archbishop) on Oct 03, 2017 at 08:30 UTC
Ah, I see. I like offloading things like this to modules, in this case I think IPC::Run would be appropriate, the following works for me. If you think the child might misbehave and not terminate on SIGINT, see the IPC::Run doc section "Timeouts and Timers" on how to time out the kill operation. `use IPC::Run qw/start/; my $h = start ['play','-q','/home/myname/soundfile.wav']; sleep 5; $h->signal('INT'); $h->finish;` [download]	[reply] [d/l]
Re^4: Killing a child process by Anonymous Monk on Oct 04, 2017 at 08:56 UTC
Re^5: Killing a child process (updated) by haukex (Archbishop) on Oct 04, 2017 at 10:50 UTC
Re^4: Killing a child process by Anonymous Monk on Oct 04, 2017 at 14:01 UTC
Re^5: Killing a child process by haukex (Archbishop) on Oct 04, 2017 at 15:25 UTC
Re: Killing a child process by Anonymous Monk on Oct 03, 2017 at 08:34 UTC
The corrected code snippet, with the usual thanks to all commenters. `#!/usr/bin/perl use strict; use diagnostics; use warnings; my $pid = fork \|\| exec 'play', '/home/ra/Desktop/trek2.mp3'; print "My PID is $pid\n"; sleep 5; kill 'KILL', $pid;` [download]	[reply] [d/l]
Re^2: Killing a child process by ikegami (Patriarch) on Oct 03, 2017 at 15:37 UTC
The approach recommended above is actually the less violent `kill INT => $pid;` [download]	[reply] [d/l]