FileTest.relative?

ruby-talk
1

It seems FileTest lacks a `relative?` method (and conversely `absolute?
`). I need such a method. I went to write one but found my self not
100% certain about it being cross-platform. I wrote:

  module FileTest
    module_function

    def relative?(path)
      /\A[\/\\]/ !~ File.expand_path(path)
    end
  end

To put it in English, I expand the path and then simply check for a
leading '/' or '\'.

I noticed Pathname has a `relative?` method and I looked at it. It's
seems a bit bulky:

    if File::ALT_SEPARATOR
      SEPARATOR_LIST = "#{Regexp.quote File::ALT_SEPARATOR}
#{Regexp.quote File::SEPARATOR}"
      SEPARATOR_PAT = /[#{SEPARATOR_LIST}]/
    else
      SEPARATOR_LIST = "#{Regexp.quote File::SEPARATOR}"
      SEPARATOR_PAT = /#{Regexp.quote File::SEPARATOR}/
    end

    def relative?
      path = @path
      while r = chop_basename(path)
        path, basename = r
      end
      path == ''
    end

    def chop_basename(path)
      base = File.basename(path)
      if /\A#{SEPARATOR_PAT}?\z/o =~ base
        return nil
      else
        return path[0, path.rindex(base)], base
      end
    end
    private :chop_basename

Is all that really necessary? My version may be too simplistic, but
surely there is more concise way to do this?

2

Pathname has both #absolute? and #relative?, as well as some other
nice methods for figuring out what a path means. Maybe look there?

Ben

···

On Tue, Dec 21, 2010 at 3:35 PM, Intransition <transfire@gmail.com> wrote:

It seems FileTest lacks a `relative?` method (and conversely `absolute?
`). I need such a method. I went to write one but found my self not
100% certain about it being cross-platform. I wrote:

3

Your code is not contemplating drive letters.

···

On Dec 21, 8:35 pm, Intransition <transf...@gmail.com> wrote:

It seems FileTest lacks a `relative?` method (and conversely `absolute?
`). I need such a method. I went to write one but found my self not
100% certain about it being cross-platform. I wrote:

module FileTest
module_function

def relative?\(path\)
  /\\A\[\\/\\\\\]/ \!\~ File\.expand\_path\(path\)
end

end

Is all that really necessary? My version may be too simplistic, but
surely there is more concise way to do this?

--
Luis Lavena

4

Good point.

···

On Dec 21, 6:52 pm, Luis Lavena <luislav...@gmail.com> wrote:

Your code is not contemplating drive letters.

5

On Windows, a path without a drive letter that only starts in a single
backslash would be relative (becuase it's relative to the current drive
letter.) A double backslash would be an absolute UNC name.

···

On Wed, 22 Dec 2010 09:06:04 +0900, Intransition wrote:

On Dec 21, 6:52 pm, Luis Lavena <luislav...@gmail.com> wrote:

Your code is not contemplating drive letters.

Good point.

--
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/