Here's a neat one by edan, that ought to work for you.

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

# by edan of perlmonks, works great
spawn(5, "xterm");
spawn(5, "xterm");
spawn(5, "xterm");
spawn(5, "xterm");

print "Hit enter to quit\n";
<>;


sub spawn
{
  my ($timeout, @cmd) = @_;
  defined( my $child_pid = fork ) or die "fork: $!";

   if ($child_pid)
      {
       # parent
         eval
             {
              local $SIG{ALRM} = sub { timeout($child_pid); };
              alarm $timeout;
              waitpid $child_pid, 0;
              alarm 0;
      };

       if ($@){print "oops: $@";}

   }else{
     # child
     exec @cmd or die "exec: $!";
    }
}

sub timeout
{
  my ($pid) = @_;
  kill 'TERM' => $pid;
  waitpid $pid, 0;
  die "reaped $pid\n";
}
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