use Fcntl qw(LOCK_EX LOCK_NB);
my $scriptname = $0; # assuming that all script instances will be invoked the same way

open my $script, $scriptname
    or die "Couldn't find myself?! Looked for '$script', but got $!";
if( !flock $script, LOCK_EX | LOCK_NB ) {
    print "We are already running\n";
    exit 1;
};

sleep 60