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Input highlighter / visual grep

by Aristotle (Chancellor)
on Dec 17, 2004 at 02:40 UTC ( #415533=sourcecode: print w/ replies, xml ) Need Help??

Category: Utility Scripts
Author/Contact Info /msg Aristotle
Description:

Inspired by pudge over at use.perl, here's a short little script you can use to highlight pattern matches in input data.

usage: hl [ -c colour ] [ -x ] pattern [ file... ] [ < input ]

You can use capturing parens in your pattern. In that case, you can supply multiple attributes separated by commas, which will be used to individually colour the submatches.

-x will supress lines without matches.

Update: fixed massive offset calculation bug, hugely simplified the colourizing routine.

Due to the semantics of the @- and @+ arrays, my first stab was a horrible monster and incredibly difficult to debug, far harder to write than it promised to be. The special entries at index 0 indicating the start and end of the entire match required terrible contortions to take into account.

And, surprise surprise, the code was buggy.

In fixing my bug, I realized that the proper special case looked almost like a common case. And then I realized that by appending a phantom zero-length match and changing index 0 to instead signify a phantom zero-length 0th match, both special cases disappear.

Lesson: when implementing the semantics turns your brain to mush, change the semantics.

For a history of the code, look at aforementioned use.perl thread.

#!/usr/bin/perl
use strict;
use warnings;

use Term::ANSIColor;
use List::Util qw( min );
use Getopt::Std;

getopts( 'c:x' );
my @color = split /,/, our $opt_c || 'bold red';

@ARGV or die <<"END_USAGE";
usage: @{[ colored( 'hl [ -c colour ] [ -x ] pattern [ file... ] [ < i
+nput ]', 'bold' ) ]}
       You can use capturing parens in your pattern. In that case,
       you can supply multiple attributes separated by commas,
       which will be used to individually colour the submatches.
       @{[ colored( '-x', 'bold' ) ]} will supress lines without match
+es.
END_USAGE

my $rx = shift;
$rx = qr/$rx/;

while ( <> ) {
    s{ $rx }{ colored_match() }gex or not( our $opt_x ) or next;
    print;
}

sub colored_match {
    my @START = @-;
    my @END = @+;
    my $last = min( $#color, $#START );

    if ( $last ) {
        push @START, $END[ 0 ];
        push @END, $END[ 0 ];
        $END[ 0 ] = $START[ 0 ];
        my $str;
        for my $i ( 0 .. $last ) {
            $str .= colored(
                substr( $_, $START[ $i ], $END[ $i ] - $START[ $i ] ),
                $color[ $i ],
            ) unless $i == 0;
            $str .= colored(
                substr( $_, $END[ $i ], $START[ $i + 1 ] - $END[ $i ] 
+),
                $color[ 0 ],
            );
        }
        return $str;
    }
    else {
        return colored(
            substr( $_, $START[ 0 ], $END[ 0 ] - $START[ 0 ] ),
            $color[ 0 ],
        );
    }
}

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