sbt: suppressing logging prefix in stdout

Question

When using sbt with forking (fork in run := true), every output from my application to stdout is prefixed by [info]; output to stderr is prefixed with [error].

This behavior is somewhat annoying when using a Java logging framework which outputs to stderr. The resulting debug messages typically look like this:

[error] [main] INFO MyClass ...
[error] [main] DEBUG MyClass ...

I would like to suppress these prefixes like when running the code without forking. What I tried:

• setting sbt -Dsbt.log.noformat=true in the sbt launch script. But this only removes colored ANSI output; prefixes are still there just without color
• setting logLevel in run := Level.Error in build.sbt. This does not seem to have any influence on logging with forking.

Is there any way to suppress the prefixes?

Answer 1

You need to set the output strategy of your project.

In my extended build I have the following settings:

settings = Project.defaultSettings ++ Seq(
  fork                  :=   true, // Fork to separate process
  connectInput in run   :=   true, // Connects stdin to sbt during forked runs
  outputStrategy        :=   Some(StdoutOutput) // Get rid of output prefix
  // ... other settings
)