Question

I have a Rakefile like this

task :clean do
  sh 'rm ./foo'
end

I want to prevent it from reporting error when the file ‘foo’ does not exist. How to do that?

I think what I want is: Is there a way to check the file first and then decide what to do next.

For example:

file 'aaa' => 'bbb' do
  sh 'cp bbb aaa'
end

This task depends on the existence of file ‘bbb’, so I want to know can I tell Rake that my task depends on the non-existence of file 'foo' ?

Answer 1

You can do this by extending rake a bit:

Rakefile:

require File.join(File.dirname(__FILE__), 'unfile_rake_ext')

unfile 'target.txt' do
  File.delete('target.txt')
end

unfile_rake_ext.rb:

class UnFileTask < Rake::FileTask
  def needed?
    File.exist?(name)
  end
end

def unfile(*args, &block)
  UnFileTask.define_task(*args, &block)
end

And my console output:

D:\Projects\ZPersonal\tmp>ls
Rakefile  unfile_rake_ext.rb

D:\Projects\ZPersonal\tmp>touch target.txt && ls
Rakefile  target.txt  unfile_rake_ext.rb

D:\Projects\ZPersonal\tmp>rake target.txt --trace
** Invoke target.txt (first_time)
** Execute target.txt

D:\Projects\ZPersonal\tmp>ls
Rakefile  unfile_rake_ext.rb

D:\Projects\ZPersonal\tmp>rake target.txt --trace
** Invoke target.txt (first_time, not_needed)

D:\Projects\ZPersonal\tmp>ls
Rakefile  unfile_rake_ext.rb

Hope this helps.