#!/usr/bin/perl 

use strict;
use warnings;

$_="four fifth two frog left leaf fred wolf foul"; 
my @F=m/\bf\w*/g; 
print "@F\n";
@F=m/\w*f\b/g; 
print "@F\n";
@F=m/\w+f\w+/g; 
print "@F\n";