preg_match_all匹配可选括号

Question

Trying to preg_match_all

#THING or [#THING]

This works for the first

/(#[A-Z]+)/ 

For the other with brackets, I thought something like this should work, but it doesn't.

/(\[?#[A-Z]+\]?)/  

Ultimately, I want to match any of these

#THING [(#THING)] or [anything(#THING)anything]

Answer 1

This seems to be a robust/reliable pattern:

~#[A-Z]+|\[[^#\]]*\(#[A-Z]+\)[^\]]*]~

Pattern Demo

~         #pattern delimiter
#[A-Z]+   #match hash symbol followed by one or more uppercase letters
|         #or
\[        #match an opening square bracket
[^#\]]*   #match zero or more non-hash/non-closing square bracket characters
\(        #match opening parenthesis
#[A-Z]+   #match hash symbol followed by one or more uppercase letters
\)        #match closing parenthesis
[^\]]*    #match zero or more non-closing square bracket characters
]         #match a closing square bracket
~         #pattern delimiter

This pattern is looking for a "hashtag" substring with no [()] characters in it OR a "hashtag" substring that will be tightly wrapped in () then loosely wrapped in [] which may also contain some characters before the ( or after the ).

This pattern is efficient because it uses greedy quantifiers and it does not employ any capture groups.