As every body suggest, I think regex will help you a lot. Here is short version perlrequick and the complete one perlre.

A few months ago I implemented something similar, here is what I did. I hope it helps for me worked just fine based on my needs. I have included some information to help you understand the process, just in case that something is a bit more complicated just let me know I will try to explain more.

#!/usr/bin/perl
use warnings;   # it warns about undefined values
use strict;     # it's a lexical scoped declaration
use Data::Dumper;
use constant ARGUMENTS => scalar 3;

$| = 1; #flushing output
my $filename; 
my $Counting = 0;
my $Characters = 0;
my $source = $ARGV[0];
my $patern = $ARGV[1];
my $target = $ARGV[2];
my $elements;
my $value;
my $lines;
my @found;
my @word;

#my $path_source = "/path/".$source."";
#my $path_destination = "/path/".$target."";

open(READ, ,"<", $source) 
    or die "Can not open ".$source.": $!\n"; # < read mode

open(WRITE, ,">", $target)
    or die "Can not open ".$target.": $!\n"; # > write mode

if (@ARGV > ARGUMENTS) {
    print "Too many argument inputs\nCorrect syntax ".$source." ".$pat
+ern." name of the file to store the data.\n";
}
elsif (@ARGV < ARGUMENTS) {
    print "Need more argument inputs\nCorrect syntax ".$source." ".$pa
+tern." name of the file to store the data.\n";
}
else {
    while ($lines = <READ>) {
    chomp ($lines); # chomp avoid \n on last field
    @word = split ((/\s+/), $lines); #\s+ = 1 or more white-space char
+acters # \d+ matches one or more integer numbers

    foreach $value (@word) {
        if ($value eq $patern) {
        push (@found, $value);
        print "I have found one matching pattern: $value\n";
        }
    }
    }
    $elements = scalar(@found);
    print "I found number of occurrences: ".$elements."\n";
    print WRITE "I found pattern: $patern, number of occurrences: $ele
+ments\n";
}

close (READ) or die "READ did not close: $!\n";
close (WRITE) or die "WRITE did not close: $!\n";

$| = 1; #flushing output
[download]

You can modified it to meet your needs in sub loop or print error conditions etc.