Obligatory Tie::File solution. I haven't done any benchmarks, but I would guess it's as fast as the other Perl solutions while being less memory-intensive.

As others have said, /bin/grep is the way to go here. 

#!/usr/bin/perl 

use strict;
use warnings;
use Tie::File;
use Fcntl 'O_RDONLY';

my $DEBUG = 0;
my $text = qr/c9391b56-b174-441b-921c-7d63/;
my $file = 'GWSvc.log';
my $context = 3;

sub dprint { print @_ if $DEBUG };

my @lines;
tie @lines, 'Tie::File', $file, mode => O_RDONLY 
    or die "tie failed: $!";

for (my $i = 0; $i <= $#lines; $i++) {
    dprint "SCAN: line $i\n";
    if ($lines[$i] =~ /$text/) {
        dprint "MATCH at line $i\n";
        my $start = $i - $context;
        if ($start < 0) {
            $start = 0;
        };
        my $end = $i + $context;
        for my $j ($start .. $end) {
            dprint "$j: ";
            print "$lines[$j]\n";
        };
        print "\n";
        $i += $context;
    };
};

[download]

In reply to Re: grab 'n' lines from a file above and below a /match/ by mrpeabody
in thread grab 'n' lines from a file above and below a /match/ by barathbr

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