RegEx for matching everything except a repeating char at start and end

Question

I have a string pattern and the examples are below.

AA4grgrsragrga4334grAA

AAA4323425AAA

AAAAAA%%%AAAAAA

Leading 'A's and trailing As always appear in pair.

I have tried:

A+.+A+

No idea how to pair up the leading As and trailing As in REGEX.

Answer 1

If you als want to match paired A's at the start and the end for strings like AA, or AAAAAA but also AAteAstAA you could use an alternation:

^(A+)(?:[^A].*[^A]|[^A])?\1$

About the pattern

• ^ Start of string
• (A+) Capture in the first group matching 1+ A's
• (?: Non capturing group
  • [^A].*[^A] Match not A, 0+ times any char except newline, then again not A
  • | Or
  • [^A] Match not A
• )? Close non capturing group and make it optional
• \1 Back reference to group 1
• $ End of string

Regex demo

If AAA can also match you can use

^(A+)(?:[^A].*[^A]|.)?\1$

Regex demo