Recursively delete empty folders in Lua

Question

I have written a script that run in WingFTP Server which has a Lua scripting engine built in. The script recursively deletes empty folders except the specified root folder.

--Walks a file tree and delete empty folders except the root folder
function EmptyFolderDeleter(options)
 local rootPath = options.path
 local path = options.path
 function walk(path)
 local currentPath = path
 --cycle through the current directory, walking directories
 for dir in c_GetDir(currentPath) do
 local fullPath = currentPath..dir.."/"
 walk(fullPath)
 end
 --if we've got this far then we're at the bottom of the tree
 --there are no more directories to visit
 --now check if there is ANYTHING (file or folder) in the current folder 
 local empty = true
 for isdir, file in c_GetFileDir(currentPath) do
 empty = false
 end
 --now check the 'empty' flag and if the folder is the root
 if empty == true and currentPath ~= rootPath then
 c_RemoveFileDir(currentPath)
 end
 end
 walk(path)
 end

The script uses three custom Lua functions that are built into WingFTP:

c_GetDir() = an iterator that returns directory names as string

c_GetFileDir() = an iterator that returns directory and file names as strings. Also returns a boolean whether the returned string is directory or not.

c_RemoveFileDir() = Deletes the specified file or folder

My script can be called like so like so:

local root = "D:/Clients/"
for dir in c_GetDir(root) do
 EmptyFolderDeleter{path=root..dir.."/"}
end

Is there is simpler or more efficient way to recursively delete empty sub folders in Lua?

Is there anything I can do to improve code readability?

Answer 1

Since you're not updating the variables path, rootPath and currentPath anywhere, use a single variable.

Define the function walk locally.

You can also break out of your c_GetFileDir loop once you've updated the empty flag. This will remove the time to iterate through all children of a directory.

The help pages for WFTPServer have a different return values for c_GetFileDir than yours!

function EmptyFolderDeleter( options )
 local root = options.path
 local walk = function( path )
 --cycle through the current directory, walking directories
 for dir in c_GetDir( path ) do
 walk( path..dir.."/" )
 end
 --if we've got this far then we're at the bottom of the tree
 --there are no more directories to visit
 --now check if there is ANYTHING (file or folder) in the current folder 
 local empty = true
 for isdir, file in c_GetFileDir( path ) do
 empty = false
 break
 end
 --now check the 'empty' flag and if the folder is the root
 if empty and path ~= root then
 c_RemoveFileDir( path )
 end
 end
 walk( root )
 end

• chazjn: Regarding c_GetFileDir in the help pages: Yes I was scratching my head for ages and then I contacted WingFTP directly who confirmed that their help pages are in fact incorrect!
• chazjn: Thanks for your tips, I feel the readability of the code has been improved. Just one note: I like the the white spacing in the function parameters, e.g. walk( root ) I have not seen this before and am surprised that I quite like it! How do you format functions with multiple parameters?
• hjpotter92: @chazjn f( a, b, {1, 2, 3}, c, d )