#!/usr/bin/perl -w

use strict;

while (<DATA>) {
    next unless /trigger/;
    while (<DATA>) {
        if ( $_ =~ /timestamp/ ) {
            print "Found timestamp\n";
            last;
        }
    }
}

__DATA__
bar
baz
trigger
qux
timestamp
quux
quuux
trigger
quuuux
timestamp
bar