Question

I have a large word list file with one word per line. I would like to filter out the words with repeating alphabets.

INPUT:
  abducts
  abe
  abeam
  abel
  abele

OUTPUT:
  abducts
  abe
  abel

I’d like to do this using Regex (grep or perl or python). Is that possible?

Answer 1

It’s much easier to write a regex that matches words that do have repeating letters, and then negate the match:

my @input = qw(abducts abe abeam abel abele);
my @output = grep { not /(\w).*\1/ } @input;

(This code assumes that @input contains one word per entry.) But this problem isn’t necessarily best solved with a regex.

I’ve given the code in Perl, but it could easily be translated into any regex flavor that supports backreferences, including grep (which also has the -v switch to negate the match).