I'm trying to create 2 separate regexes for strings that have these two patterns

STTSHP.COM

• uppercase
• one letter repeats ONLY twice
• no digits
• only ever 6 letters before the .com

YNGFUV.COM

• uppercase
• no letter repeats
• no digits
• only ever 6 letters before the .com

I came up with this regex, but it doesn't seem to be working. What about it is wrong?

^(?=(?:[A-Z\D]*[A-Z]{6})(?:([A-Z\D])(?!.*\1)){6}\.COM$

CodePudding user response：

Based on my understanding of the problem here is a regex that would fulfil all conditions:

^([A-Z])(?![A-Z]*\1)(?:([A-Z])\2(?!\2)(?:([A-Z])(?![A-Z]*\3)){3}|(?:([A-Z])(?![A-Z]*\4)){5})\.COM$

RegEx Demo

RegEx Details:

• ^: Start
• ([A-Z]): Match an uppercase letter and capture in group #1
• (?!\1): Make sure first letter is not repeated
• (?:: Stare non-capture group
  • ([A-Z])\2: Match an uppercase letter and capture in group #2. Match same letter again using \2.
  • (?!\2): Make sure same letter is not repeated again 3rd time
  • (?:([A-Z])(?!\3)){3}: Match any 3 letters ensure there are no adjacent repeats
  • |: OR
  • (?:([A-Z])(?!\4)){5}: Match 5 uppercase letter that don't allow any adjacent repeats
• ): End non-capture group
• \.COM: Match .COM
• $: End

CodePudding user response：

You can assert that there are no 3 of the same uppercase chars.

^(?![A-Z]*([A-Z])[A-Z]*\1[A-Z]*\1)[A-Z]{6}\.COM$

The pattern in parts matches:

• ^ Start of string
• (?! Negative lookahead, assert what to the right is not
  • [A-Z]*([A-Z])[A-Z]*\1[A-Z]*\1 Match 3 of the same uppercase chars
• ) Close the lookahead
• [A-Z]{6}
• \.COM$ Match .COM at the end of the string

See a regex 101 demo.