#!/usr/bin/perl -w
use strict;

$| = 1;

use Getopt::Std;

my %opts;
getopts( 'p:f:s:h', \%opts );
my $pattern = $opts{p} || "pdf";
my $sleep = $opts{'s'} || 5;
my $logfile = shift || "/tmp/a.log";

my $fh = select( STDOUT ); $|=1; select( $fh );

print "watching file '$logfile' for pattern '$pattern'\n";

open(LOGFILE, "<" . $logfile) or die "not readable: '$logfile'$!\n";

seek(LOGFILE, 0, 2);
while (1) {
    while (<LOGFILE>) {
        print if /$pattern/o;
    }
    sleep $sleep;
    seek(LOGFILE, 0, 1);
}