my $str = 'TEST:foo:bar:123:A:B';

print 'split:  ', (split ':', $str)[1],        $/;
print 'substr: ', substr($str, 5, 3),          $/;
print 'regex:  ', $str =~ /:([a-z]+)/,         $/;
print 'grep:   ', grep(/^f/, split /:/, $str), $/;

__output__

split:  foo
substr: foo
regex:  foo
grep:   foo