Regular expression to match character repeated three times

Question

I need to simplify the following regular expression to include all the letters of the alphabet:

(a{3})|(b{3})|(c{3})|(z{3})|(A{3})|(B{3})|(C{3})|(Z{3})
         


        

Answer 1

Use backreferences. Eg. in sed:

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

or in PERL regular expressions

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