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 letter I am looking for ahead of time.

This is a question I was asked in interviews and then asked in interviews. Not so many people get it correct.

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'