use strict;
use warnings;
use Data::Dumper;

# this is how far forward or back you need to read
my $width  = 200;

# this is your target string.  You can make it a regex if you prefer
my $target = 'search';

# file to search
my $file   = 'test.txt';
my $fsize  = -s $file;

# when you're done, this should contain the data you're looking for
my @chunks;


open FILE, "< $file" or die "Cannot open $file for reading: $!";

while (<FILE>)
{
    if ( /$target/g )
    {
        my $file_position = tell FILE;

        # backwards from end of string
        my $word_position = $file_position - (length( $_ ) - pos( $_ )
+);
        # to beginning of word.  It's separate so you can
        # pull it out if necessary.
        $word_position -= length $target;
        push @chunks, get_chunk( \*FILE, $word_position, $file_positio
+n, $width, $fsize );
    }
}

print Dumper \@chunks;

close FILE;

sub get_chunk
{
    my ( $fh, $word_position, $file_position, $width, $fsize ) = @_;

    # don't try to read before beginning of file
    my $start = $word_position >= $width
        ? $word_position - $width
        : 0;

    # don't try to read after end of file
    my $end   = $word_position + $width <= $fsize
        ? $word_position + $width
        : $fsize;

    # position to start of where we want to read
    seek $fh, $start, 0;
    my $chunk;

    # shouldn't fail unless I got my boundaries wrong
    read ( $fh, $chunk, $end-$start ) or die "Problem reading file: $!
+";

    # put us back to where we were
    seek $fh, $file_position, 0;
    return $chunk;
}
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.