Cri is a library for building easy-to-use commandline tools with support for nested commands.
The central concept in Cri is the command, which has option definitions as well as code for actually executing itself. In Cri, the commandline tool itself is a command as well.
Here’s a sample command definition:
command = Cri::Command.define do
name 'dostuff'
usage 'dostuff [options]'
aliases :ds, :stuff
summary 'does stuff'
description 'This command does a lot of stuff. I really mean a lot.'
flag :h, :help, 'show help for this command' do |value, cmd|
puts cmd.help
exit 0
end
flag nil, :more, 'do even more stuff'
option :s, :stuff, 'specify stuff to do', :argument => :required
run do |opts, args, cmd|
stuff = opts.fetch(:stuff, 'generic stuff')
puts "Doing #{stuff}!"
if opts[:more]
puts 'Doing it even more!'
end
end
end
To run this command, invoke the #run
method with the raw arguments. For
example, for a root command (the commandline tool itself), the command could
be called like this:
command.run(ARGV)
Each command has automatically generated help. This help can be printed using
Cri::Command#help
; something like this will be shown:
usage: dostuff [options] does stuff This command does a lot of stuff. I really mean a lot. options: -h --help show help for this command --more do even more stuff -s --stuff specify stuff to do
Let’s disect the command definition and start with the first five lines:
name 'dostuff'
usage 'dostuff [options]'
aliases :ds, :stuff
summary 'does stuff'
description 'This command does a lot of stuff. I really mean a lot.'
These lines of the command definition specify the name of the command (or the commandline tool, if the command is the root command), the usage, a list of aliases that can be used to call this command, a one-line summary and a (long) description. The usage should not include a “usage:” prefix nor the name of the supercommand, because the latter will be automatically prepended.
Aliases don’t make sense for root commands, but for subcommands they do.
The next few lines contain the command’s option definitions:
flag :h, :help, 'show help for this command' do |value, cmd|
puts cmd.help
exit 0
end
flag nil, :more, 'do even more stuff'
option :s, :stuff, 'specify stuff to do', :argument => :required
Options can be defined using the following methods:
-
Cri::CommandDSL#option
orCri::CommandDSL#opt
-
Cri::CommandDSL#flag
(implies no arguments passed to option) -
Cri::CommandDSL#required
(implies required argument) -
Cri::CommandDSL#optional
(implies optional argument)
All these methods take the short option form as their first argument, and a
long option form as their second argument. Either the short or the long form
can be nil, but not both (because that would not make any sense). In the
example above, the --more
option has no short form.
Each of the above methods also take a block, which will be executed when the
option is found. The argument to the block are the option value (true
in
case the option does not have an argument) and the command.
The last part of the command defines the execution itself:
run do |opts, args, cmd|
stuff = opts.fetch(:stuff, 'generic stuff')
puts "Doing #{stuff}!"
if opts[:more]
puts 'Doing it even more!'
end
end
The Cri::CommandDSL#run method takes a block with the actual code to execute. This block takes three arguments: the options, any arguments passed to the command, and the command itself.
Instead of defining a run block, it is possible to declare a class, the
command runner class (Cri::CommandRunner
) that will perform the actual
execution of the command. This makes it easier to break up large run blocks
into manageable pieces.
Commands can have subcommands. For example, the git
commandline tool would be
represented by a command that has subcommands named commit
, add
, and so on.
Commands with subcommands do not use a run block; execution will always be
dispatched to a subcommand (or none, if no subcommand is found).
To add a command as a subcommand to another command, use the
Cri::Command#add_command
method, like this:
root_cmd.add_command(cmd_add)
root_cmd.add_command(cmd_commit)
root.cmd.add_command(cmd_init)
-
Toon Willems
-
Ken Coar
Thanks for Lee “injekt” Jarvis for Slop, which has inspired the design of Cri 2.0.