This will match each occurence of a string inside a file:

#!/usr/bin/perl -w

use strict;
use IO::File;

use constant FILE => 'search.txt';
use constant FIND => 'string to find';

IO::File->input_record_separator(FIND);

my $fh = IO::File->new(FILE, O_RDONLY)
  or die 'Could not open file ', FILE, ": $!";

$fh->getline;  #fast forward to the first match

#print each occurence in the file
print IO::File->input_record_separator
  while $fh->getline;

$fh->close;
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Explanation: The input record seperator, $/ has been set to your search string. When perl reads the file line by line, it actually is scanning the file until it finds the search string, printing the string each time it finds it. To my knowledge this is the fastest way to do brute force exact text matches in a file with pure perl.