use Mutex;

my $mutex = Mutex->new( path => $0 );  # choose $0 or tmp path
my $mutex = Mutex->new( path => "/tmp/db.lock" );
 
# The script terminates after some time if a previous
# instance is still running with a held lock.

exit unless $mutex->timedwait( 5 );    # seconds

# Has exclusive lock at this point. Due to using flock,
# the lock is released no matter how the process dies,
# even if omitting $mutex->unlock.

# Do DB insert here.

$mutex->unlock;

# Do other things, optionally.

...