How would I do pattern matching on this string in lua?

Question

I have a string which contains a path to a file:

C:\Users\user\directory\build.bat

Is there a way I can remove the word between the last backslash and the second last backslash (in this case it is directory), however I would like a way to do this several times:

First time I run the code the path should look like this:

C:\Users\user\build.bat

If I run the code on the new string I just got from running the program the first time, the output should be like this:

C:\Users\build.bat

Answer 1

Yes, this is very much possible. I propose the following pattern:

^(.+)\.-\(.-)$ - this will match the entire path, matching first the directories up to the parent directory and then the filename. Use it as follows:

local function strip_parent_dir(path)
    local path_to_parent, filename = path:match[[^(.+)\.-\(.-)$]]
    return path_to_parent .. "\\" .. filename
end

which can then be used as follows:

print(strip_parent_dir[[C:\Users\user\directory\build.bat]]) -- C:\Users\user\build.bat
print(strip_parent_dir(strip_parent_dir[[C:\Users\user\directory\build.bat]])) -- C:\Users\build.bat

another option would be to split the path by the path delimiter (backslash), inserting the parts into a table, then removing the penultimate entry, finally concatenating the parts; this is slightly longer but may be considered more readable (and it may have better asymptotic performance):

local function strip_parent_dir(path)
    local parts = {}
    for part in path:gmatch"[^\\]+" do
        table.insert(parts, part)
    end
    table.remove(parts, #parts - 1)
    return table.concat(parts, "\\")
end

the results are the same. Choose whatever you consider more readable.