#!/usr/bin/perl
use strict;
use warnings;
$_="four fifth two frog left leaf fred wolf foul";
my @F=m/\bf.*?\b/g;
print "@F";

##</code><code>##

$_="four fifth two frog left leaf fred wolf";
my @F=m/\b.*?f\b/g;
print "@F";

##</code><code>##

$_="four fifth two frog left leaf fred wolf";
my @F=m/\b[^f].*?f.*?\b/g;
print "@F";