Question

I am not too familiar with regex and so I been having some getting this to work with Apple’s NSRegularExpression

I am trying to remove words in parentheses or brackets…

For example:

NSString *str = @”How do you (remove parentheses words) within a string using”

resulting string should be: @”How do you within a string using”

Thanks you!!!

Answer 1

Search for

\([^()]*\)

and replace with nothing.

As a verbose regex:

\(      # match an opening parenthesis
[^()]*  # match any number of characters except parentheses
\)      # match a closing parenthesis

This will work fine if parentheses are correctly balanced and unnested. If parentheses can be nested (like this (for example)), then you need to re-run the replace until there are no further matches, since only the innermost parentheses will be matched in each run.*

To remove brackets, do the same with \[[^[\]]*\], for braces \{[^{}]*\}.

With conditional expressions you could do all three at once, but the regex looks ugly, doesn’t it?

(?:(\()|(\[)|(\{))[^(){}[\]]*(?(1)\))(?(2)\])(?(3)\})

However, I’m not sure if NSRegularExpression can handle conditionals. Probably not. Explanation of this monster:

(?:           # start of non-capturing group (needed for alternation)
 (\()         # Either match an opening paren and capture in backref #1
 |            # or
 (\[)         # match an opening bracket into backref #2
 |            # or
 (\{)         # match an opening brace into backref #3
)             # end of non-capturing group
[^(){}[\]]*   # match any number of non-paren/bracket/brace characters
(?(1)\))      # if capturing group #1 matched before, then match a closing parenthesis
(?(2)\])      # if #2 matched, match a closing bracket
(?(3)\})      # if #3 matched, match a closing brace.

*_{You can’t match arbitrarily nested parentheses (since these constructs are no longer regular) with regular expressions, so that’s not a limitation of this regex in particular but of regexes in general.}