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.

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;
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I wonder if there's any way to check that the sound file is still playing?

I checked $h{STATE}, but its value only changes from 2 to 3 once we apply the $h->signal('INT')

I also considered piping the output into a text file, and checking it periodically, since SoX displays a nice 'Done' when the sound file finishes playing. However, that won't help us if the end user specifies an audio package other than SoX.

(This is a reply to Re^5)

Your suggestions have provided the right answer! Here are two scripts; the first hangs until the sound file stops playing, and then displays a confirmation message.

#!/usr/bin/perl

use strict;
use diagnostics;
use warnings;

use IPC::Run qw/start/;
use POSIX ":sys_wait_h";

my ($h, $pid, $result);

# Play the sound file
$h = start ['play','-q','/home/ra/Desktop/trek3.mp3'];

# Get the process ID (there's only one)
foreach my $kid (@{ $h->{KIDS} }) {

    $pid = $kid->{PID};
}

# Wait for the sound file to stop playing, and then display a message

# Option 1: scripts hangs, and then correctly displays a message 
#   as soon as the sound file stops playing
sleep 5;
waitpid($pid, 0);
print "finished!\n";

# Tidy up
$h->signal('INT');
$h->finish;
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The second checks once a second, and prints a confirmation message within a second of the sound file stopping.

#!/usr/bin/perl

use strict;
use diagnostics;
use warnings;

use IPC::Run qw/start/;
use POSIX ":sys_wait_h";

my ($h, $pid, $result);

# Play the sound file
$h = start ['play','-q','/home/ra/Desktop/trek3.mp3'];

# Get the process ID (there's only one)
foreach my $kid (@{ $h->{KIDS} }) {

    $pid = $kid->{PID};
}

# Wait for the sound file to stop playing, and then display a message

# Option 2: correctly displays a message within a second of the sound 
#   file stopping playing
do {
    sleep 1;
    waitpid($pid, WNOHANG);
    print "waiting...\n";
} until (! (kill 0, $pid));
print "finished!\n";

# Tidy up
$h->signal('INT');
$h->finish;
[download]