I'm trying to match a pair of special characters, while excluding the enclosed content from the match. For example, ~some enclosed content~ should match only the pair of ~ and leave out some enclosed content entirely. I can only use vanilla PCRE, and capture groups aren't an option.
My match criteria for the entire string is ~([^\s].*?(?<!\s))~. Matching the first and second ~ separately would also be acceptable.
Looking at your pattern, you want a non whitespace char right after the opening ~ and a non whitespace char right before the closing ~
As those are the delimiters, and the non whitespace char should also not be ~ itself, you might use:
~(?=[^~\s](?:[^~\r\n]*[^\s~])?~)|(?<=~)[^\s~](?:[^~\r\n]*[^\s~])?\K~
Explanation
~ Match literally(?= Positive lookahead, assert that to the right is
[^~\s] Match a non whitespace char except for ~(?: Non capture group
[^~\r\n]*[^\s~] Match repeating any char other than a newline or ~ followed by a non whitespace char except for ~)? Close non capture group and make it optional (to also match a single char ~a~)~ Match literally) Close the lookahead| Or(?<=~) Positive lookbehind, assert ~ to the left[^\s~] Match a non whitespace char except for ~(?:[^~\r\n]*[^\s~])? Same optional pattern as in the lookahead\K Forget what is matched so far~ Match literally