#Check the frequency!

#!/usr/bin/perl

use warnings;
use strict;

sub frequency {
    my $text = join('', @_);
    my %letters;
    foreach (split //, $text) {
        $letters{$_}++;
    }
    return %letters;
}

my $text = "this is a test";

my %count = frequency($text);

foreach (sort keys %count) {
    print "\t", $count{$_}, " '$_", ($count{$_} == 1)? "'": "'s", "\n";
}

   
    
 #Match zero or one characters!

$p = "This is a pattern test.";

if ($p =~ /(\w)?/){ print "$1\n"; }

   
    
#To specify a maximum number of occurrences, use 0 as the lower bound.!

/de{0,3}f/ matches d, followed by no more than three es, followed by f. 

   
    
 #To specify a minimum number of occurrences, leave off the upper bound.!

/de{3,}f/ matches d, followed by at least three es, followed by f. 

   
    
#Checking for multiple occurrences!

Pattern     Interpretation
/a{1,4}/    Matches one, two, three, or four as.
/a{2}/      Matches two as.
/a{0,2}/    Matches one or two as.