How to pass command line arguments to a rake task

I have a rake task that needs to insert a value into multiple databases.

I'd like to pass this value into the rake task from the command line, or from another rake task.

How can I do this?

You can specify formal arguments in rake by adding symbol arguments to the task call. For example:

require 'rake'

task :my_task, [:arg1, :arg2] do |t, args|
  puts "Args were: #{args} of class #{args.class}"
  puts "arg1 was: '#{args[:arg1]}' of class #{args[:arg1].class}"
  puts "arg2 was: '#{args[:arg2]}' of class #{args[:arg2].class}"
end

task :invoke_my_task do
  Rake.application.invoke_task("my_task[1, 2]")
end

# or if you prefer this syntax...
task :invoke_my_task_2 do
  Rake::Task[:my_task].invoke(3, 4)
end

# a task with prerequisites passes its 
# arguments to it prerequisites
task :with_prerequisite, [:arg1, :arg2] => :my_task #<- name of prerequisite task

# to specify default values, 
# we take advantage of args being a Rake::TaskArguments object
task :with_defaults, :arg1, :arg2 do |t, args|
  args.with_defaults(:arg1 => :default_1, :arg2 => :default_2)
  puts "Args with defaults were: #{args}"
end

Then, from the command line:

> rake my_task[1,false]
Args were: {:arg1=>"1", :arg2=>"false"} of class Rake::TaskArguments
arg1 was: '1' of class String
arg2 was: 'false' of class String

> rake "my_task[1, 2]"
Args were: {:arg1=>"1", :arg2=>"2"}

> rake invoke_my_task
Args were: {:arg1=>"1", :arg2=>"2"}

> rake invoke_my_task_2
Args were: {:arg1=>3, :arg2=>4}

> rake with_prerequisite[5,6]
Args were: {:arg1=>"5", :arg2=>"6"}

> rake with_defaults
Args with defaults were: {:arg1=>:default_1, :arg2=>:default_2}

> rake with_defaults['x','y']
Args with defaults were: {:arg1=>"x", :arg2=>"y"}

As demonstrated in the second example, if you want to use spaces, the quotes around the target name are necessary to keep the shell from splitting up the arguments at the space.

Looking at the code in rake.rb, it appears that rake does not parse task strings to extract arguments for prerequisites, so you can't do task :t1 => "dep[1,2]". The only way to specify different arguments for a prerequisite would be to invoke it explicitly within the dependent task action, as in :invoke_my_task and :invoke_my_task_2.

Note that some shells (like zsh) require you to escape the brackets: rake my_task\['arg1'\]

Options and dependencies need to be inside arrays:

namespace :thing do
  desc "it does a thing"
  task :work, [:option, :foo, :bar] do |task, args|
    puts "work", args
  end
  
  task :another, [:option, :foo, :bar] do |task, args|
    puts "another #{args}"
    Rake::Task["thing:work"].invoke(args[:option], args[:foo], args[:bar])
    # or splat the args
    # Rake::Task["thing:work"].invoke(*args)
  end

end

Then

rake thing:work[1,2,3]
=> work: {:option=>"1", :foo=>"2", :bar=>"3"}

rake thing:another[1,2,3]
=> another {:option=>"1", :foo=>"2", :bar=>"3"}
=> work: {:option=>"1", :foo=>"2", :bar=>"3"}

NOTE: variable task is the task object, not very helpful unless you know/care about Rake internals.

RAILS NOTE:

If running the task from Rails, it's best to preload the environment by adding => [:environment] which is a way to setup dependent tasks.

  task :work, [:option, :foo, :bar] => [:environment] do |task, args|
    puts "work", args
  end

In addition to answer by kch (I didn't find how to leave a comment to that, sorry):

You don't have to specify variables as ENV variables before the rake command. You can just set them as usual command line parameters like that:

rake mytask var=foo

and access those from your rake file as ENV variables like such:

p ENV['var'] # => "foo"

If you want to pass named arguments (e.g. with standard OptionParser) you could use something like this:

$ rake user:create -- --user [email protected] --pass 123

note the --, that's necessary for bypassing standard Rake arguments. Should work with Rake 0.9.x, <= 10.3.x.

Newer Rake has changed its parsing of --, and now you have to make sure it's not passed to the OptionParser#parse method, for example with parser.parse!(ARGV[2..-1])

require 'rake'
require 'optparse'
# Rake task for creating an account

namespace :user do |args|
  desc 'Creates user account with given credentials: rake user:create'
  # environment is required to have access to Rails models
  task :create do
    options = {}
    OptionParser.new(args) do |opts|
      opts.banner = "Usage: rake user:create [options]"
      opts.on("-u", "--user {username}","User's email address", String) do |user|
        options[:user] = user
      end
      opts.on("-p", "--pass {password}","User's password", String) do |pass|
        options[:pass] = pass
      end
    end.parse!

    puts "creating user account..."
    u = Hash.new
    u[:email] = options[:user]
    u[:password] = options[:pass]
    # with some DB layer like ActiveRecord:
    # user = User.new(u); user.save!
    puts "user: " + u.to_s
    puts "account created."
    exit 0
  end
end

exit at the end will make sure that the extra arguments won't be interpreted as Rake task.

Also the shortcut for arguments should work:

 rake user:create -- -u [email protected] -p 123

When rake scripts look like this, maybe it's time to look for another tool that would allow this just out of box.

I've found the answer from these two websites: Net Maniac and Aimred.

You need to have version > 0.8 of rake to use this technique

The normal rake task description is this:

desc 'Task Description'
task :task_name => [:depends_on_taskA, :depends_on_taskB] do
  #interesting things
end

To pass arguments, do three things:

1. Add the argument names after the task name, separated by commas.
2. Put the dependencies at the end using :needs => [...]
3. Place |t, args| after the do. (t is the object for this task)

To access the arguments in the script, use args.arg_name

desc 'Takes arguments task'
task :task_name, :display_value, :display_times, :needs => [:depends_on_taskA, :depends_on_taskB] do |t, args|
  args.display_times.to_i.times do
    puts args.display_value
  end
end

To call this task from the command line, pass it the arguments in []s

rake task_name['Hello',4]

will output

Hello
Hello
Hello
Hello

and if you want to call this task from another task, and pass it arguments, use invoke

task :caller do
  puts 'In Caller'
  Rake::Task[:task_name].invoke('hi',2)
end

then the command

rake caller

will output

In Caller
hi
hi

I haven't found a way to pass arguments as part of a dependency, as the following code breaks:

task :caller => :task_name['hi',2]' do
   puts 'In Caller'
end