my @matches;
....
while(<>) {
    my @matches    = $_ =~ m/$string/g;
    my $repetition = @matches;
    print "$string was encountered $repetition times.\n" if($repetition > 0); 
}

##</code><code>##

use strict;
use warnings;

my $text = "match other match not useful match sample word";
my $string = "match";
my @matches = $text =~ m/$string/g;
my $count = @matches;
print $count;