Question

I have been trying to find a solution to this for some time. I have found questions and answers on recursion but nothing that seemed to fit this particular situation.

I have written a class which should go through the given folder and all subfolders and rename files and folders if a particular search pattern is found.

Everything works as expected the replaceAllInDir gets called, it replaces files and folders if needed. The next step then is to do the same for all subfolders within the given folder.
So a subfolder gets identified and replaceAllInDir gets called from within itself. Let’s assum the particular subfolder called does not contain any subfolders. I would then expect that we return to the parent folder and continue looking for other subfolders. But instead control is not returned to the parent calling method and the program ends.

I am aware of other ways of solving the actual use case, but I cannot explain the behaviour of ruby.

class MultiFileAndFolderRename
  attr_accessor :rootDir, :searchPattern, :replacePattern

  def initialize(rootDir, searchPattern, replacePattern)
    @rootDir = rootDir
    @searchPattern = searchPattern
    @replacePattern = replacePattern
  end

  def execute
    replaceAllInDir(@rootDir)
  end

  def getValidDirEntries(dir)
    dirList = Dir.entries(dir)
    dirList.delete('.')
    dirList.delete('..')
    dirList
  end

  def replaceAllInDir(currentDir)
    Dir.chdir(currentDir)
    puts "Processing directory: " + Dir.pwd
    dirList = getValidDirEntries(currentDir)
    dirList.each { |dirEntry|
      attemptRename(dirEntry)
    }

    dirList = getValidDirEntries(currentDir)
    dirList.each { |dirEntry|
      if File.directory?(dirEntry)
        newDir = currentDir + '\\' + dirEntry
        rntemp = MultiFileAndFolderRename.new(newDir, 'searchString', 'replaceString')
        rntemp.replaceAllInDir(newDir)
      end
    }
  end

  def attemptRename(dirEntry)
    if dirEntry.match(@searchPattern)
      newname = dirEntry.to_s.sub(@searchPattern, @replacePattern)
      FileUtils.mv(dirEntry.to_s, newname)
    end
  end
end

Answer 1

You have a bug. The first line of replaceAllInDir() is Dir.chdir(). chdir() changes the directory of the current process on a global scale. It’s not call-stack dependent. So later when you move into a subdirectory and change into that, the change becomes permanent even if you return from the recursion.

You need to change back to the correct directory after any call to replaceAllInDir(). For example:

...
dirList.each { |dirEntry|
  if File.directory?(dirEntry)
    ....
    rntemp.replaceAllInDir(newDir)
    Dir.chdir(currentDir) # <- Restore us back to the correct directory
  end
}