It's time for everyone's favorite "i love my hammer, everything looks like a nail" post :) I have sung the praises of POE numerous times, and I am here once again to do so. POE is an event driven framework, you my friend, have events... so, I think that this sample code might be the kind of thing that you are looking for.

#!/usr/bin/perl -w

use strict;

use POE;
use POE::Session;
use POE::Wheel::FollowTail;

sub usage {
    "test.pl file_to_watch timeout [debug]\n";
}

my $file_name = shift(@ARGV) or die usage();
my $time_out  = shift(@ARGV) or die usage();
my $debug     = shift(@ARGV) || 0;

my $to_match  = "I AM LOOKING FOR THIS";

my $session = POE::Session->create(
    inline_states => {
        #Called upon POE Kernel initialization, this method
        #is what we use to set up our environment.

        _start => sub {
            my ($heap, $session) = @_[ HEAP, SESSION ];

            print "Starting parent session ".$session->ID."\n"
                if ($debug >= 1);

            #POE::Wheel::FollowTail is one of those great POE
            #modules.  It basically will sit there and emit an
            #event every time that a "record" has been added to the
            #file.  Since I did not give it a Filter, it is just
            #going to read line by line, but you could do some crazy
            #things with it :)

            $heap->{tail} = POE::Wheel::FollowTail->new(
                Filename => $file_name,
                PollInterval => 1,
                InputEvent => "input_event",
            );
        },

        #This is the event that will be called every time the wheel
        #emits an InputEvent.  It's just a cheesy skeleton, but it
        #should give you a good idea as to what *you* need to do.
        input_event => sub {
            my ($kernel, $heap, $input) = @_[ KERNEL, HEAP, ARG0 ];

            print "Input: $input" if ($debug >= 2);

            if ($input =~ /$to_match/o) {
                #IMPORTANT: this is where I'm setting the delay event
                $kernel->delay(do_action => $time_out);
                print "input matched in P::W::F::InputEvent\n"
                    if $debug;
            } else {
                print "input did not match in P::W::F::InputEvent\n"
                    if $debug;
            }
        },

        #After every line that matches, I will be called after
        #$time_out time :)
        do_action => sub {
            print "I am doing some action!\n" if $debug;
        },
    },
);

$poe_kernel->run();
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