pcre2 - Regex match to distinct letters only

Question

I am trying to create a regex that matches the following criteria below

first letter is uppercase
remaining 5 letters following the first letter are lowercase
ends in ".com"
no letter repeats only before the ".com"
no digits
there are only 5 lowercase letters before the .com, with only the first letter being uppercase

The above criteria should match to strings such as: Amipsa.com Ipsamo.com

I created this regex below, but the regex seem to capture repeating letters - examples here: https://regex101.com/r/wwJBmc/1

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

Would appreciate any insight.

user_5424988 · Answer

You might use

^(?i)[a-z]*?([a-z])[a-z]*?\1(?-i)(*SKIP)(*F)|[A-Z][a-z]{5}\.com$

Regex demo

Explanation

^ Start of string
(?i) Case insensitive match
[a-z]*?([a-z])[a-z]*?\1 Match 2 of the same chars a-z A-Z
(?-i) Turn of case insenstive
(*SKIP)(*F) Skip the match
[A-Z][a-z]{5} Match A-Z and 5 chars a-z
\.com Match .com
$ End of string

Another idea if you are using Javascript and you can not use (?i) is to use 2 patterns, 1 for checking not a repeated character with a case insensitive flag /i and 1 for the full match.

const rFullMatch = /^[A-Z][a-z]{5}\.com$/;
const rRepeatedChar = /^[a-z]*([a-z])[a-z]*\1/i;
[
  "Regxas.com",
  "Ipsamo.com",
  "Plpaso.com",
  "Amipsa.com",
  "Ipsama.com",
  "Ipsima.com",
  "IPszma.com",
  "Ipsamo&.com",
  "abcdef.com"
].forEach(s => {
  if (!rRepeatedChar.test(s) && rFullMatch.test(s)) {
    console.log(`Match: ${s}`);
  }
});

user_548225 · Answer

You may use this regex in PCRE with a negative lookahead:

^(?!(?i)[a-z]*([a-z])[a-z]*\1)[A-Z][a-z]{5}\.com$

Updated RegEx Demo

RegEx Details:

^: Start
(?!: Start negative lookahead
- (?i): Enable ignore case modifier
- [a-z]*: Match 0 or more letters
- ([a-z]): Match a letter and capture in group #1
- [a-z]*: Match 0 or more letters
- \1: Match same letter as in capture group #1
): End negative lookahead
[A-Z][a-z]{5}: Match 5 lowercase letters
\.com: Match .com
$: End

pcre2 - Regex match to distinct letters only

2 Answers