sbt - How to change log level from command line?

Question

How can I change the log level in sbt at the command line without modifying the existing configuration?

Answer 1

As described in Change the logging level globally for sbt:

To set the logging level before any commands are executed on startup, use -- before the logging level

There are four logging levels:

• debug
• info
• warn
• error

If you need one applied "at the command line without modifying the existing configuration", execute the sbt launcher with appropriate level prefixed with double dashes.

jacek:~/oss/scalania
$ sbt --debug
[debug] > boot
[debug] > reload
[debug] > sbtStashOnFailure
[debug] > onFailure load-failed
[debug] > loadp
[info] Loading global plugins from /Users/jacek/.sbt/0.13/plugins
[debug] Running task... Cancelable: false, check cycles: false
[debug]

With sbt.boot.properties you may get sbt internal logs printed out, too. See Launcher Specification.