Coursier

2.1.0-RC6

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launch

launch launches applications from their name, or directly from one or more Maven dependencies. The applications need not be installed with install.

$ cs launch scalafmt -- --help
scalafmt 3.0.6
Usage: scalafmt [options] [<file>...]

  -h, --help               prints this usage text
  -v, --version            print version
…

Like the install command, launch accepts an optional version number. A typical use case is to start a Scala REPL with a specific Scala version:

$ cs launch scala:2.12.15
Welcome to Scala 2.12.15 (OpenJDK 64-Bit Server VM, Java 1.8.0_292).
Type in expressions for evaluation. Or try :help.

scala>

In order to launch an application that does not have a published application descriptor, launch accepts Maven coordinates as well:

$ cs launch org.scalameta::scalafmt-cli:2.4.2 -- --help
scalafmt 2.4.2
Usage: scalafmt [options] [<file>...]

  -h, --help               prints this usage text
  -v, --version            print version
…

Arguments

Pass arguments to the launched program, by adding -- after the coursier arguments, like

$ cs launch scalafmt -- --version
scalafmt 3.1.1

Main class

If the dependencies don't specify a default main class via their manifest, or if the heuristics of the launch command fails to pick the right manifest, you can specify a main class via -M or --main-class, like

$ cs launch com.lihaoyi:ammonite_2.13.1:2.0.4 -M ammonite.Main
Loading...
Welcome to the Ammonite Repl 2.0.4 (Scala 2.13.1 Java 1.8.0_121)
@

If a dependency is published by sbt, and contains only one main class, the main class should have been automatically added to the manifest. If it contains several main classes, setting mainClass in sbt is required for it to be set in the manifest.

In case several of the loaded JARs have manifests with main classes, the launch command applies an heuristic to try to find the "main" one.

If the heuristic to find the main class fails, pass -v -v to launch to get more details:

$ cs launch com.geirsson:scalafmt-cli_2.12:1.5.1 -r bintray:scalameta/maven -v -v -- --version
…
Found main classes:
  com.martiansoftware.nailgun.NGServer (vendor: , title: )
  org.scalafmt.cli.Cli (vendor: com.geirsson, title: cli)
…

This prints the main classes of all manifests found, among other things. If you think one of them is the right one, just pass it via -M to launch.

Java options

With the native coursier launcher, you can pass options to the JVM that launch starts with --java-opt, like

$ cs launch --java-opt -Dfoo=bar --java-opt -Xmx2g ammonite
Loading...
Welcome to the Ammonite Repl 2.2.0-4-4bd225e (Scala 2.13.3 Java 11.0.2)
@ sys.props("foo")
res0: String = "bar"
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