From: dblack@...
Date: 2007-08-29T08:57:08+09:00
Subject: Re: Deleting empty directories

Hi --

On Wed, 29 Aug 2007, Paul van Delst wrote:

> Hello,
>
> I'm putting together a script to automatically update a repository working 
> copy. The scenario is such that the versioned working copy itself is not 
> being modified, but I am simply rsync'ing changes from an unversioned source 
> (i.e. just a bunch of directories), and then committing (and then tagging) 
> those files. It sounds weird, I know, but it's just temporary. Honest.
>
> Anyway, the need has arisen to delete empty directory heirarchies (rsync will 
> delete the files but not the directories because of the .svn subdirs). What 
> I've done so far is this:
>
>  require 'fileutils'
>
>  def empty_dirs
>    @current.collect do |f|
>      f if (File.directory?(f) && Dir.glob("#{f}/*").empty?)
>    end.compact
>  end
>
>  def remove_empty_dirs
>    while not empty_dirs.empty?
>      empty_dirs.each {|d| FileUtils.rm_rf(d)}
>    end
>  end
>
> where the @current contains the updated list of files in my versioned working 
> copy after I rsync'd, but before I started comparing the changes in my 
> working copy. I created a dummy repository with a relatively complicated 
> heirarchy of directories to test the above and it seems to work. However, two 
> things bug me:
>
> Firstly, in empty_dirs, I think
>
>  f if (File.directory?(f) && Dir.glob("#{f}/*").empty?)
>
> looks ugly. My limited experience is that if something looks ugly it can 
> usually be expressed better. I haven't used collect too much either, so its 
> intricacies escape me.

You're currently using collect plus compact, but you can actually just
use select. (That's not a general equivalence, but in this case it
applies.)

   @current.select do |f|
     File.directory?(f) && Dir["#{f}/*"].empty?
   end

I'd be inclined to break things out a little. (Untested code follows
-- please test on expendable data :-)

   require 'fileutils'

   def dirs
     @current.select {|f| File.dir?(f) }
   end

   def empty_dirs
     dirs.select {|d| Dir["#{d}/*"].empty? }
   end

   def non_empty_dirs
     dirs - empty_dirs
   end

   def remove_empty_dirs
     non_empty_dirs.each {|d| FileUtils.rm_rf(d) }
   end

> Secondly, I prefer not to test for negatives, as in
>
>  while not empty_dirs.empty?

You can use until instead of while not.

> I also would rather not have an open loop either, but if a directory contains 
> empty subdirectories, the parent directory is not considered empty, and etc. 
> etc. As you can probably tell, recursion is not my strong point.
>
> Would any kind soul out there care to provide any pointers for cleaning up 
> the methods above?
>
> Thanks for any info,
>
> cheers,
>
> paulv
>
> p.s. BTW, I think the remove_empty_dirs method still needs to remove the 
> deleted directories from @current to prevent them being tested again in the 
> next call to empty_dirs.

Or you can reset @current before each call, or some combination. I
haven't done either in my sample code; I'm just assuming that @current
is what it should be, but you'll definitely have to factor that in.


David

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