Given a path, how to determine if its absolute/relative in Ruby?

Question

I am working on writing a rake build scrip which will work cross platform ( Mac OSX, Linux , Windows ). The build script will be consumed by a CI server .

I want the logic of my script to be as follows:

1. If the path is determined to be relative, make it absolute by making output_path = FOO_HOME + user_supplied_relative_path
2. If the path is determined to be absolute, take it as-is

I'm currently using Pathname.new(location).absolute? but it's not working correctly on windows.

What approach would you suggest for this?

Answer 1

require 'pathname'
(Pathname.new "/foo").absolute? # => true
(Pathname.new "foo").absolute? # => false

Answer 2

The method you're looking for is realpath.

Essentially you do this:

absolute_path = Pathname.new(path).realpath

NB: The Pathname module states that usage is experimental on machines that do not have unix like pathnames. So it's implementation dependent. Looks like JRuby should work on Windows.

Answer 3

There is a built-in function that covers both cases and does exactly what you want:

output_path = File.absolute_path(user_supplied_path, FOO_HOME)

The trick is supplying a second argument. It servers as a base directory if (and only if) the first argument is a relative path.

Answer 4

Pathname can do all that for you

require "pathname"
home= Pathname.new("/home/foo")

home + Pathname.new("/bin") # => #<Pathname:/bin>
home + Pathname.new("documents") # => #<Pathname:/home/foo/documents>

I am not sure about this on windows though.

Answer 5

You could also use File.expand_path if the relative directory is relative to the current working directory.

I checked on Linux and windows and didn't have any issues.

Assuming FOO_HOME is the working directory, the code would be:

output_path = File.expand_path user_supplied_relative_path