Search text with a regular expression to match outside specific characters - regex

Question

I have text that looks like:
My name is (Richard) and I cannot do
[whatever (Jack) can't do] and
(Robert) is the same way [unlike
(Betty)] thanks (Jill)
The goal is to search using a regular expression to find all parenthesized names that occur anywhere in the text BUT in-between any brackets.
So in the text above, the result I am looking for is:
Richard
Robert
Jill

Answer 1

You can do it in two steps:
step1: match all bracket contents using:
\[[^\]]*\]
and replace it with ''
step2: match all the remaining parenthesized names(globally) using:
\([^)]*\)

Answer 2

You didn't say what language you're using, so here's some Python:
>>> import re
>>> REGEX = re.compile(r'(?:[^[(]+|\(([^)]*)\)|\[[^]]*])')
>>> s="""My name is (Richard) and I cannot do [whatever (Jack) can't do] and (Robert) is the same way [unlike (Betty)] thanks (Jill)"""
>>> filter(None, REGEX.findall(s))
The output is:
['Richard', 'Robert', 'Jill']
One caveat is that this does not work with arbitrary nesting. The only nesting it's really designed to work with is one level of parens in square brackets as mentioned in the question. Arbitrary nesting can't be done with just regular expressions. (This is a consequence of the pumping lemma for regular languages.)
The regex looks for chunks of text without brackets or parens, chunks of text enclosed in parens, and chunks of text enclosed in brackets. Only text in parens (not in square brackets) is captured. Python's findall finds all matches of the regex in sequence. In some languages you may need to write a loop to repeatedly match. For non-paren matches, findall inserts an empty string in the result list, so the call to filter removes those.

Answer 3

IF you are using .NET you can do something like:
"(?<!\[.*?)(?<name>\(\w+\))(?>!.*\])"

Answer 4

It's not really the best job for a single regexp - have you considered, for example, making a copy of the string and then deleting everything in between the square brackets instead? It would then be fairly straight forward to extract things from inside the parenthesis. Alternatively, you could write a very basic parser that tokenises the line (into normal text, square bracket text, and parenthesised text, I imagine) and then parses the tree that produces; it'd be more work initially but would make life much simpler if you later want to make the behaviour any more complicated.
Having said that, /(?:(?:^|\])[^\[]*)\((.*?)\)/ does the trick for your test case (but it will almost certainly have some weird behaviour if your [ and ] aren't matched properly, and I'm not convinced it's that efficient).
A quick (PHP) test case:
preg_match_all('/(?:(?:^|\])[^\[]*)\((.*?)\)/', "My name is ... (Jill)", $m);
print(implode(", ", $m[1]));
Outputs:
Richard, Robert, Jill

Answer 5

>>> s="My name is (Richard) and I cannot do [whatever (Jack) can't do (Jill) can] and (Robert) is the same way [unlike (Betty)] thanks (Jill)"
>>> for item in s.split("]"):
... st = item.split("[")[0]
... if ")" in st:
... for i in st.split(")"):
... if "(" in i:
... print i.split("(")[-1]
...
Richard
Robert
Jill

Answer 6

So you want the regex to match the name, but not the enclosing parentheses? This should do it:
[^()]+(?=\)[^\[\]]*(?:\[[^\[\]]*\][^\[\]]*)*$)
As with the other answers, I'm making certain assumptions about your target string, like expecting parentheses and square brackets to be correctly balanced and not nested.
I say it should work because, although I've tested it, I don't know what language/tool you're using to do the regex matching with. We could provide higher-quality answers if we had that info; all regex flavors are not created equal.