I’m running into a problem with this regex for TCP Flag validation.
Here is my current version (I’ve been though many, all are wrong in some way):
^([AFPRSU](?![0-9]))(?!1)|((?<![A-z])[1-9]+[0-9]*)$
So, the value can either be any non-repeating combination of TCP Flags (A,F,P,R,S,U) or the integer equivalent.
Valid:
A,
AFP,
FPURA,
18,
1,
40
Invalid:
empty/null/whitespace,
AA,
aFP,
a100,
100a,
XFP
The problem with my current regex is the lookaheads/behinds only check one character +/- so AFPx100 will be a valid value since “F” after “A” is valid. I had similar issues with different iterations, but ultimately it boils down to ignorance. I’ve been using trial and error on regexr.com but not really getting anywhere, been about 8 hours of effort so far.
I’m unfortunately bound to Regex or I would solve this a different way. At this point I’m desperate for any pointers/advice. Thanks.