How can I find repeated letters with a Perl regex?

Question

I am looking for a regex that will find repeating letters. So any letter twice or more, for example:

booooooot or abbott

I won\'t know the

Answer 1

You can find any letter, then use \1 to find that same letter a second time (or more). If you only need to know the letter, then $1 will contain it. Otherwise you can concatenate the second match onto the first.

my $str = "Foooooobar";

$str =~ /(\w)(\1+)/;

print $1;
# prints 'o'
print $1 . $2;
# prints 'oooooo'

Answer 2

I think you actually want this rather than the "\w" as that includes numbers and the underscore.

([a-zA-Z])\1+

Ok, ok, I can take a hint Leon. Use this for the unicode-world or for posix stuff.

([[:alpha:]])\1+

Answer 3

Just for kicks, a completely different approach:

if ( ($str ^ substr($str,1) ) =~ /\0+/ ) {
    print "found ", substr($str, $-[0], $+[0]-$-[0]+1), " at offset ", $-[0];
}

Answer 4

The following code will return all the characters, that repeat two or more times:

my $str = "SSSannnkaaarsss";

print $str =~ /(\w)\1+/g;

Answer 5

/(.)\\1{2,}+/u

'u' modifier matching with unicode

Answer 6

I Think using a backreference would work:

(\w)\1+

\w is basically [a-zA-Z_0-9] so if you only want to match letters between A and Z (case insensitively), use [a-zA-Z] instead.

(EDIT: or, like Tanktalus mentioned in his comment (and as others have answered as well), [[:alpha:]], which is locale-sensitive)