my $str = 'aaa\bbb\ccc\ddd\eee\fff';
if ($str =~ /(\w+\\){3}(\w+)(\\\w+){2}/) {
    print $2;
}

my $str = 'aaa\bbb\ccc\ddd\eee\fff';
my $str_got = (split /\\/, $str)[3];
print $str_got;

'aaa\bbb\ccc\ddd\eee\fff' =~ /\bbbb\b/;
print "$&\n";

print ${\((split'\\\\','aaa\bbb\ccc\ddd\eee\fff')[1])};