How would I add something like a "--version" argument to a program?

[nessus42]

I'm writing a CLI program that has a complex bunch of arguments, many of which are required. But kind of like how "--help" bypasses the necessity for the rest of the command line to exist, I'd also like a "--version" option that would behave similarly and just cause the program to output its version number and exit successfully. How can I accomplish this in any easy manner?

I suppose that I could always include the version in the program summary that is output by "--help", but ideally I'd like to have a separate option for the version number.

[bkirwi]

So, two answers:

• If you're using CommandApp, you can pass a version string to the constructor, like so:

  decline/core/jvm/src/test/scala/com/monovore/example/decline/ListDir.scala

  Lines 7 to 10 in f6752ea

  	extends CommandApp(
  	name = "ls",
  	header = "List information about files.",
  	version = "1.0",

• You can implement your own --version option quite easily also:

let programOpts = ??? // your normal program options go here
let versionOpts = Opts.flag("version", "Print version information and exit").map(_ => println("Version 1.0"))
let opts = programOpts orElse versionOpts

CommandApp's version flag is actually implemented like this under the hood.

Many people start by just using orElse for subcommands, but it's a pretty powerful feature. I endorse reaching for it anytime you have mutually-exclusive sets of options.

[nessus42]

Thanks!!!