How can I use regex to match strings if the regex has nested group?
pattern-matching, regex, scala
Solution
`.*` 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.
Problem
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?