Setting system properties with "sbt run"

Question

I'm using a pretty recent version of SBT (seems to be hard to figure out what the version is). I want to pass system properties to my application with sbt run as follows:

sbt -Dmyprop=x run

How could I do that?

Answer 1

SBT's runner doesn't normally create new processes, so you also have to tell it to do this if you want to set the arguments that are passed. You can add something like this to your build settings:

fork := true

javaOptions := Seq("-Dmx=1024M")

There's more detail on forking processes in the SBT documentation.

Answer 2

I found the best way to be adding this to build.sbt:

// important to use ~= so that any other initializations aren't dropped
// the _ discards the meaningless () value previously assigned to 'initialize'
initialize ~= { _ =>
  System.setProperty( "config.file", "debug.conf" )
}

Related: When doing this to change the Typesafe Configuration that gets loaded (my use case), one needs to also manually include the default config. For this, the Typesafe Configuration's suggested include "application" wasn't enough but include classpath("application.conf") worked. Thought to mention since some others may well be wanting to override system properties for precisely the same reason.

Source: discussion on the sbt mailing list