Regex nested optional groups - regex

Question

I am trying to capture the bold part of strings like this:
'capture a year range at the end of a string 1995-2010'
'if there's no year range just capture the single year 2005'
'capture a year/year range followed by a parenthesis, including the parenthesis 2007-2012 (58 months)'
This regex works for 1 and 2, but I can't get it to work for 3:
/(\d+([-–— ]\d+( \(\d+ months\))?)?$)/
What am I doing wrong?

Answer 1

Try this regex:
/\d{4}(?:[-–— ]\d{4})?(?:\s*\([^)]+\))?$/gm
This one captures everything in the brackets.
If you need a regex specific to the text "(number) months" in the brackets, then you can use this: \d{4}(?:[-–— ]\d{4})?(?:\s+\(\d+\smonths\))?$
Link to test: RegexPal or RegExr
Sample text:
capture a year range at the end of a string 1995-2010
if there's no year range just capture the single year 2005
capture a year/year range followed by a parenthesis, including the
parenthesis 2007-2012 (58 months)
trying out another example 1990 (23 weeks)
trying out another example 1995-2002 (x days)
trying out another example 2050 (blah blah)
trying out another example 2050—3000
trying out another example 2050-3000
trying out another example 2050–3000
And the JavaScript code:
var regex = /\d{4}(?:[-–— ]\d{4})?(?:\s*\([^)]+\))?$/gm; //multiline enabled
var input = "your input string";
if(regex.test(input)) {
var matches = input.match(regex);
for(var match in matches) {
alert(matches[match]);
}
} else {
alert("No matches found!");
}

Answer 2

This Regex works nicely. :)
/(?:(?:\d{4}[-–— ])?\d{4})(?: \(\d+ months\))?$/
The main difference between my Regex and Jonah's is that mine contains ?: which means not to capture the sub-groups. When you group in a Regex it automatically returns what is in that group unless you tell it not to, and I've found that sometimes when those groups get captured when using methods such as replace or split, that it can be a little buggy which may be your problem as well.

Answer 3

The following regex works for me in a sample Perl script. It should be workable in JavaScript:
/(\d{4}([-–— ]\d{4})?( \(\d+ months\))?)$/
We first match a 4-digit year: \d{4}
Then we match an optional separator followed by another 4-digit year: ([-–— ]\d{4})?
Finally, we match the optional months portion: ( \(\d+ months\))?
You may need to insert whitespace matches (\s*) where needed, if your data doesn't always follow this strict template.

Answer 4

It actually works fine here, if I understand your needs correctly: Gskinner RegExr
Just alternate which sentence is the last, as $ will not count for newlines, just the end of the string.