Here's a filter version (read from stdin, write to stdout) of this, um, filter. I've also added the before/after context parameters as program options. (Consistent with the grep utility.)

Note the use of a small queue (@lines) to buffer the before-context. And notice the versatility of the splice function.

#!/usr/bin/env perl

use strict;
use warnings;
use Getopt::Std;

my @patterns = (
    qr/error/i,
    qr/FATAL/,
    qr/Critical/,
    qr/exception/,
);
my $re = join '|', @patterns;

my %opt = ( B => 5, A => 5 );
getopts('B:A:', \%opt);

my $window = $opt{B} + $opt{A} + 1;
my $emit = 0;
my @lines;

while (<>) {
    $emit = $window if /$re/;
    splice(@lines, 0, 0, $_);
    --$emit < 0 ? splice(@lines, $opt{B}) : print splice(@lines, -1);
}

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Edit: above code is deficient both at the start and end of the stream. See if you can fix it...

In reply to Re: Print 5 lines before and after pattern match from a list by oiskuu
in thread Print 5 lines before and after pattern match from a list by jayu_rao

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