added chop_path

lib/fs/alias.rb

@@ -15,6 +15,7 @@ module Alias
       :ln      => :link,
       :dir?    => :directory?,
       :expand  => :expand_path,
+      :chop    => :chop_path,
       :[]      => :join,
     }
 

lib/fs/base.rb

@@ -173,6 +173,20 @@ def expand_path(path, base=nil)
       File.expand_path(path, base)
     end
 
+    # chop base from the path
+    # if it's not a subdir the absolute path will be returned
+    def chop_path(path, base='.')
+      full_base = File.expand_path(base)
+      full_path = File.expand_path(path)
+      if full_path == full_base
+        '.'
+      elsif full_path.start_with?(full_base)
+        full_path[full_base.size+1..-1]
+      else
+        full_path
+      end
+    end
+
     # checks for a slash at the beginning
     def absolute?(path)
       %r{\A/} =~ path ? true : false

spec/base_spec.rb

@@ -440,6 +440,37 @@
     end
   end
 
+  describe '::chop_path' do
+    it 'does nothing for relative paths' do
+      FS.chop_path('.').should eql('.')
+      FS.chop_path('./foo').should eql('foo')
+      FS.chop_path('foo').should eql('foo')
+      FS.chop_path('foo/bar').should eql('foo/bar')
+    end
+
+    it 'does not chop for non subdirs' do
+      FS.chop_path('/').should eql('/')
+      FS.chop_path('..').should eql(File.expand_path('..'))
+      FS.chop_path('/foo', '/foo/bar').should eql('/foo')
+    end
+
+    it 'chop absolute the path' do
+      here = File.expand_path('.')
+      FS.chop_path(here).should eql('.')
+      FS.chop_path(File.join(here, '.')).should eql('.')
+      FS.chop_path(File.join(here, 'foo')).should eql('foo')
+      FS.chop_path(File.join(here, 'foo/bar')).should eql('foo/bar')
+      FS.chop_path('/foo/bar').should eql('/foo/bar')
+    end
+
+    it 'uses a base dir to chop the path' do
+      FS.chop_path('.', '.').should eql('.')
+      FS.chop_path('/', '/').should eql('.')
+      FS.chop_path('/foo', '/foo').should eql('.')
+      FS.chop_path('/foo/bar', '/foo').should eql('bar')
+    end
+  end
+
   describe '::absolute?' do
     it 'checks for an absolute path' do
       FS.absolute?('/').should be_true