SBT: Cross-platform way to set java.library.path?

Question

I was working on a project that requires loading of native libraries, and so far, all development was restricted to Linux. In order to run my project, I could simply enable forking and modify java.library.path as follows:

javaOptions in run += "-Djava.library.path=some/common/path:lib/native/linux"

My question is: How can I do the same in a cross-platform way, so that I can share my build.sbt with a Windows-based developer. There are in particular three things that I couldn't figure out so far:

• I know that SBT allows to construct platform-independent paths like "dir1" / "dir2", but I'm not aware of a cross-platform way to join multiple paths (since it is : on Linux and ; on Windows).
• Is it possible to append either lib/native/linux or lib/native/windows dependent on the platform?
• My approach above overwrites java.library.path -- is it possible to append instead?

Gheber

Answer 1

Since you can use any Scala code, you can of course do

val folderName =
  if (System.getProperty("os.name").startsWith("Windows")) "windows" else "linux"

val libPath = Seq("some/common/path", s"lib/native/$folderName").mkString(java.io.File.pathSeparator)

javaOptions in run += s"-Djava.library.path=$libPath"

though this doesn't answer your last question.

Gilmore

This is looking good. I forgot to mention that I'm still using SBT 0.12 and, in general, I was hoping for a version agnostic solution. But I think this idea works in 0.12 as well. I still have a hard time to use SBT's / syntax though, since there is no implicit conversion from String to (I guess) File. But obviously there is always the work-around of doing it manually with separatorChar. And for debugging purposes: Any idea why show java-options always just returns List()? – Gheber

Yes, this should work fine in 0.12. Except, IIRC, it uses Scala 2.9 for build configuration, so string interpolation should be replaced with +. For the last question, I don't know. Maybe ask it separately? – Gilmore

What about System.getProperty("java.library.path") and do the concatenation yourself? – Bieber

I guess my mistake was to assume that SBT must have a nice idiomatic solution for all that (like with modifying the classpath for instance). The idea of doing this manually just felt wrong to me. But overall: Problem solved. – Gheber