#!/usr/bin/perl

use strict;
use warnings;

# use Tie::File;

my @lines = <DATA>;
my $last_idx = $#lines;

for (0 .. $last_idx) {
   print @lines[$_-1 .. $_+2] if $lines[$_] =~ /ggg/;
}

__DATA__
aaa
bbb
ccc
ddd
eee
fff
ggg
hhh
iii
jjj
kkk
lll
mmm