Here's an improved version.

• The old version always waited for at least the timeout period, even if the command completed early.

  This one returns as soon as the external command terminates.

• The old version returned nothing if the process timed out.

  This version will return as much as was available before the process was killed.

• It also addresses a potential "Uninitialised" warning if the system is heavily loaded and the thread takes a while to start.

  If the thread or process was slow starting due to system load or other factors, the old version could try to use $pid before it was set. This corrects that error.

#! perl -slw
use strict;
use threads;
use threads::shared;

$|++;

our $N ||= 11;
my $TIMEOUT = 10;
my $extApp = q[ perl -lwe"$|++; print $_ and sleep 1 for 1 .. $ARGV[0]
+" ];

my @results :shared;
my $pid :shared;

async {
    $pid = open my $fh, "$extApp $N |" or die "$!, $^E";
    push @results, $_ while <$fh>;
}->detach;

sleep 1 until $pid;
sleep 1 while kill 0, $pid and $TIMEOUT--;
kill 3, $pid and warn 'Command timed out' if $TIMEOUT;

print "command return \n'@results'";
__END__
C:\test>timeoutcmd -N=1
command return
'1
'

C:\test>timeoutcmd -N=10
command return
'1
 2
 3
 4
 5
 6
 7
 8
 9
 10
'

C:\test>timeoutcmd -N=11
Command timed out at C:\test\timeoutcmd.pl line 21.
command return
'1
 2
 3
 4
 5
 6
 7
 8
 9
 10
 11
'
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