Regex - alternating character matching pattern

Question

I want to match patterns of alternating lowercase characters.

ababababa -> match 

I tried this

 ([az][az])+[az] 

but it will also be a match

 ababxyaba 

Answer 1

You can use this regex with 2 backlinks to match alternating lowercase letters:

 ^([az])(?!\1)([az])(?:\1\2)*\1?$ 

RegEx Demo

RegEx Distribution:

• ^ : Start
• ([az]) : match the first letter in capture group # 1
• (?!\1) : Lookahead to make sure we don't repeat the same letter.
• ([az]) : match the second letter in capture group # 3
• (?:\1\2)* : match zero or more pairs of the first and second letters
• \1? : Match the optional first letter to the end
• $ : End