匹配可选的捕获组

Question

I want to match an xml element and create a group for an optional attribute. If the attribute does not exist then i'm going to perform some other action. For example i have

<customer display="no">

I want to match on the customer element but the display attribute might not exist. In code i was going to check to see if that capture group is empty and if so perform some custom logic.

so the regex i have is

<customer.*(display="yes|no").*?>

That matches the element ok when it has the attribute but how can i make the group optional so i can check to see if the element was included?

Answer 1

You can just put a question mark after the group, the same as any other optional component of a regex. You will also have to make the first .* lazy (by adding ? ) if you do this, otherwise it will consume the whole line.

So you should have something like this:

<customer.*?(display="yes|no")?.*?>

Also note that (display="yes|no") probably doesn't match what you want it to: it matches display="yes or no" not display="yes" or display="no" . I suspect you want (display="(?:yes|no)") instead.

Answer 2

Try this regex:

<customer.*?(display="(?:yes|no)").*?>

explain:

?

Matches the previous element zero or one time.

*?

Matches the previous element zero or more times, but as few times as possible.

(?: subexpression)

Defines a noncapturing group.