Bug #2731: FileUtils.copy prints error message in $DEBUG mode when destination doesn't exist
http://redmine.ruby-lang.org/issues/show/2731

Author: Kornelius Kalnbach
Status: Open, Priority: Normal
Category: lib
ruby -v: ruby 1.9.2dev (2010-02-04 trunk 26573) [i386-darwin10.2.0]

Trying to copy a file with Ruby:

$ touch source
$ ls destination
ls: destination: No such file or directory
$ ruby -rfileutils -d -e 'FileUtils.copy "source", "destination"'
Exception `Errno::ENOENT' at /usr/local/lib/ruby/1.9.1/fileutils.rb:1429 - No such file or directory - destination
$ ls destination 
destination

While the copy succeeds, it prints this confusing message. I don't expect libraries to issue exceptions when performing standard operations. This affects the FileUtils methods install, mv, cp_r, and cp; but the problem is in Entry_#fu_same? (around lib/fileutils.rb:1426):

  def fu_same?(a, b)   #:nodoc:
    if fu_have_st_ino?
      st1 = File.stat(a)
      st2 = File.stat(b)
      st1.dev == st2.dev and st1.ino == st2.ino
    else
      File.expand_path(a) == File.expand_path(b)
    end
  rescue Errno::ENOENT
    return false
  end

So, File.stat(b) is checked even if b doesn't exist. The resulting error message is even explicitely captured and hidden by the rescue. For the methods in question, it is a common case that the destination file doesn't exist.

Here's a version that doesn't rely on exceptions:

  def fu_same?(a, b)   #:nodoc:
    return false if !File.exist?(a) || !File.exist?(b)
    if fu_have_st_ino?
      st1 = File.stat(a)
      st2 = File.stat(b)
      st1.dev == st2.dev and st1.ino == st2.ino
    else
      File.expand_path(a) == File.expand_path(b)
    end
  end

The problem exists across Ruby versions from 1.8.6 to 1.9.2dev.


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