#!/usr/bin/perl -w

use strict;

my $logfile = "/path/to/logfile";
my $outfile = "/path/to/outfile";
my $find    = "hello";

my $second  = '';
my $first   = '';
my $line    = 0;

# allow regex unfriendly chars in $find
$find = quotemeta $find; 

open (FILE, "<$logfile") or die "Oops perl says $!";
while (<FILE>) {
    chomp;
    $line++;
    &print_found if /$find/;
    $second = $first;
    $first  = $_;
}

sub print_found {
    open (OUT, ">>$outfile") or die "Oops perl says $!";
    print OUT "Line: $line\n";
    print OUT "$second\n$first\n$_\n\n";
    close OUT;
}