How can I use regex to match strings if the regex has nested group?

Question

There are some strings:

111/aaa
111/aaa|222/bbb

They are in the form of expression:

(.*)/(.*)(|(.*)/(.*))?

I tried to use it to match a string and extract the values:

var rrr = """(.*)/(.*)(|(.*)/(.*))?""".r

"123/aaa|444/bbb" match {
    case rrr(pid,pname, cid,cname) => println(s"$pid, $pname, $cid, $cname")
    case _ => println("not matched ?!")
}

But it prints:

not matched ?!

And I want to get:

123, aaa, 444, bbb

How to fix it?

UPDATE

Thanks for @BartKiers and @Barmar's anser, that I found my regex has several mistakes, and finally found this solution:

var rrr = """(.*?)/(.*?)([|](.*?)/(.*?))?""".r

"123/aaa|444/bbb" match {
    case rrr(pid,pname, _, cid,cname) => println(s"$pid, $pname, $cid, $cname")
    case _ => println("not matched ?!")
}

It works, but you can see there is a _ which is actually not useful. Is there any way to redefine the regex that I can just write rrr(pid,pname,cid,cname) to match it?

| is a special character in regexp, you need to escape it. — Barmar
– Barmar, Commented Jul 5, 2013 at 6:58
Yes, if there are groups that you use just for the pattern, not to capture, that's what non-capture groups are for. — Barmar
– Barmar, Commented Jul 5, 2013 at 8:01

Freewind · Accepted Answer · 2013-07-14 02:19:44Z

5

.* could lead to a lot of backtracking becuase .* would first match the complete string and then go back one by one until it matches the first /.

Also it won't capture the values in groups properly as you would expect it to..

You should use .*?

Your regex should be

^(.*?)/(.*?)(?:\|(.*?)/(.*?))?$

There wouldn't be any performance difference for small strings but it would capture the values in the right group

Notice the ?: in the regex, it means don't capture the group (?:\|(.*?)/(.*?))?. So it will be 4 subgroups only as the result.

edited Jul 14, 2013 at 2:19

Freewind

199k163 gold badges457 silver badges740 bronze badges

answered Jul 5, 2013 at 7:02

Anirudha

32.9k8 gold badges71 silver badges90 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Bart Kiers · Accepted Answer · 2013-07-05 06:58:41Z

3

Try to escape the |, which is the logical OR in regex:

var rrr = """(.*)/(.*)(\|(.*)/(.*))?""".r

answered Jul 5, 2013 at 6:58

Bart Kiers

171k38 gold badges307 silver badges297 bronze badges

Collectives™ on Stack Overflow

How can I use regex to match strings if the regex has nested group?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related