How do I match a pattern with optional surrounding quotes?
This is quite simple as well: (".+"|.+). Make sure the first match is with quotes and the second without.
You can get a solution without repeating by making use of backreferences and conditionals:
/^(")?(pattern)(?(1)\1|)$/
Matches:
- pattern
- "pattern"
Doesn't match:
- "pattern
- pattern"
This pattern is somewhat complex, however. It first looks for an optional quote, and puts it into backreference 1 if one is found. Then it searches for your pattern. Then it uses conditional syntax to say "if backreference 1 is found again, match it, otherwise match nothing". The whole pattern is anchored (which means that it needs to appear by itself on a line) so that unmatched quotes won't be captured (otherwise the pattern in pattern" would match).
Note that support for conditionals varies by engine and the more verbose but repetitive expressions will be more widely supported (and likely easier to understand).
Update: A much simpler version of this regex would be /^(")?(pattern)\1$/, which does not need a conditional. When I was testing this initially, the tester I was using gave me a false negative, which lead me to discount it (oops!).
I'll leave the solution with the conditional up for posterity and interest, but this is a simpler version that is more likely to work in a wider variety of engines (backreferences are the only feature being used here which might be unsupported).