Proc::Pidfile is a very simple OO interface which manages a pidfile
for the current process.  You can pass the path to a pidfile to use as
an argument to the constructor, or you can let Proc::Pidfile choose
one (basically, "/var/run/$basename", if you can write to /var/run,
otherwise "/$tmpdir/$basename").

WWW: http://search.cpan.org/dist/Proc-Pidfile/