Re: Print 5 lines before and after pattern match from a list

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);
}
[download]

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

Comment on Re: Print 5 lines before and after pattern match from a list Select or Download Code

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Re^2: Print 5 lines before and after pattern match from a list by ww (Archbishop) on Mar 15, 2015 at 16:00 UTC
I don't think the attribute "deficient" applies so much to your code as to OP's imperfect spec. Clearly, if an element of `@patterns` occurs in first line of the log being read, lines `( -n .. 0 )` simply do NOT exist (for any value other than 0 of the prior lines desired). We can speculate, but OP alone knows (or 'should know') the complete spec. Similarly, if any element of `@patterns` occurs in the last line, the lines `( (last+1)..(last+5) )` are going to be a bit difficult to include in the output. BUT, far more important than the observations above, your code (Re: Print 5 lines before and after pattern match from a list) and that above same title, different node, by bitingduck are excellent examples of what Monks can do to help a Seeker, as is hdb's initial response re the looping mistake and Athanasius' note on regular expressions. ++ to all. Spirit of the Monastery	[reply] [d/l] [select]
Re^3: Print 5 lines before and after pattern match from a list by hdb (Monsignor) on Mar 15, 2015 at 17:19 UTC
The OPs code already implements a solution by cutting of at the beginning and the end of the array, so we can safely imply his desired spec!	[reply]