Hello BlueStarry, and welcome to the Monastery!

If the entire file will fit in memory, a variation on kennethk’s solution is to simply delete the newlines before searching:

#! perl
use strict;
use warnings;

my $target = 'kitten';
my $string =  do { local $/; <DATA>; };
   $string =~ s/\n//g;
my $count  = () = $string =~ /\Q$target/g;

print "The target string '$target' occurs $count times in the file\n";

__DATA__
sushikitten
ilovethekit
tensushithe
kittenisthe
[download]

Output:

14:28 >perl 1474_SoPW.pl
The target string 'kitten' occurs 3 times in the file

14:28 >
[download]

However, as your input file is 5 GB, this approach is probably impractical. In which case you’re going to have to bite the bullet and implement a solution with “strange buffers” — such as a sliding window technique. Maybe have a look at Data::Iterator::SlidingWindow.

Hope that helps,

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