use strict;
use warnings;

my $five10 = $] > 5.010 ? 1 : 0;

while (<DATA>) {
    my $regex = '\b' . substr $_,0,1;
    foreach my $letter (split //, substr($_,1)) {
        $regex .= '(?:' . $letter;
    }
    $regex .= (')?' . '+' x $five10) x ((length)-1) . '\b';
    print $regex;
}

__DATA__
hello