How can I match a quote-delimited string with a regex?

Question

If I\'m trying to match a quote-delimited string with a regex, which of the following is \"better\" (where \"better\" means both more efficient and less likely to do somethi

Answer 1

More complicated, but it handles escaped quotes and also escaped backslashes (escaped backslashes followed by a quote is not a problem)

/(["'])((\\{2})*|(.*?[^\\](\\{2})*))\1/

Examples:
  "hello\"world" matches "hello\"world"
  "hello\\"world" matches "hello\\"

Answer 2

Considering that I didn't even know about the "*?" thing until today, and I've been using regular expressions for 20+ years, I'd vote in favour of the first. It certainly makes it clear what you're trying to do - you're trying to match a string that doesn't include quotes.

Answer 3

From a performance perspective (extremely heavy, long-running loop over long strings), I could imagine that

"[^"]*"

is faster than

".*?"

because the latter would do an additional check for each step: peeking at the next character. The former would be able to mindlessly roll over the string.

As I said, in real-world scenarios this would hardly be noticeable. Therefore I would go with number two (if my current regex flavor supports it, that is) because it is much more readable. Otherwise with number one, of course.

Answer 4

I'd say the second one is better, because it fails faster when the terminating " is missing. The first one will backtrack over the string, a potentially expensive operation. An alternative regexp if you are using perl 5.10 would be /"[^"]++"/. It conveys the same meaning as version 1 does, but is as fast as version two.

Answer 5

I would suggest:

([\"'])(?:\\\1|.)*?\1

But only because it handles escaped quote chars and allows both the ' and " to be the quote char. I would also suggest looking at this article that goes into this problem in depth:

http://blog.stevenlevithan.com/archives/match-quoted-string

However, unless you have a serious performance issue or cannot be sure of embedded quotes, go with the simpler and more readable:

/".*?"/

I must admit that non-greedy patterns are not the basic Unix-style 'ed' regular expression, but they are getting pretty common. I still am not used to group operators like (?:stuff).

Answer 6

I'd go for number two since it's much easier to read. But I'd still like to match empty strings so I would use:

/".*?"/