Question

Say I want to make a regex that splits a optional version number from a file name i.e

val regex(name, ver) = "file.jar"          // name = file, ver = empty
val regex(name, ver) = "some-software.jar" // name = some-software, ver = empty
val regex(name, ver) = "software-1.0.jar"  // name = software, ver = 1.0
val regex(name, ver) = "some-file-1.0.jar" // name = some-file, ver = 1.0

How is such a regular expression written in Scala/Java ?. In perl I would do something along the lines of:

(.*)(-(\d|.)*)?.jar

but Scala does not seam to support making optional groups in this syntax.

Answer 1

I am not sure what your question now is.

I assume it is not matching the second group, because the first one is greedy and since the second is optional, the first matches everything.

Try this:

(.*?)(?:-(?=\d)(.*))?.jar

See it here on Regexr

1. I made the first group a lazy match with the .*?
2. The second group is a non capturing group (the one starting with (?:. You will find the name now in group 1 and the version in group 2.
3. I put a lookahead after the dash, so that it searches for a dash followed by a digit.