$SIG{ALRM} = sub { exit; };

alarm 60 * 60 * 2;

##</code><code>##

open(F, ">$wherever/myscript.pid") or warn "myscript.pid: $!\n";
print F "$$\n";
close(F);

$SIG{TERM} = sub { exit; };

END {
   unlink "$wherever/myscript.pid";
}

##</code><code>##

[ -r $wherever/myscript.pid ] && kill `cat $wherever/myscript.pid`