Here's a simple fork/exec with an alarm. It won't cleanup multiple processes so it must use the >1 arg version of exec. I think you might already know that exec with more than 1 argument avoids using sh.

#!/usr/bin/env perl
use warnings;
use strict;

my $ksecs = 5;
my $csecs = 10;
my $sig = 2;

my $pid = fork;
die "fork: $!" unless(defined $pid);

if($pid == 0){
    exec 'sleep', $csecs; # >1 arg exec to avoid using sh
    die "failed to spawn command: $!";
}

local $SIG{'ALRM'} = sub { kill $sig, $pid };
alarm $ksecs;
waitpid $pid, 0; # waitpid sets $?
alarm 0; # turn off alarm in case child finished before parent

if($? == $sig){
    # we killed it (or someone else sent the same signal)
}elsif($?){
    # child had another error or signal
}
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