Embed Directive in Lua

Here’s the translation of the Go code to Lua, formatted in Markdown suitable for Hugo:

Our example demonstrates how to include arbitrary files and folders in the Lua program at runtime. In Lua, we don’t have a built-in embed directive, but we can achieve similar functionality using the io library.

-- Import the io library
local io = require("io")

-- Function to read file contents
local function readFile(path)
    local file = io.open(path, "rb") -- r read mode and b binary mode
    if not file then return nil end
    local content = file:read("*all")
    file:close()
    return content
end

-- Read the contents of single_file.txt
local fileString = readFile("folder/single_file.txt")

-- Read the contents of single_file.txt as bytes
local fileByte = readFile("folder/single_file.txt")

-- Function to read multiple files from a folder
local function readFolder(folderPath, pattern)
    local lfs = require("lfs")
    local folder = {}
    for file in lfs.dir(folderPath) do
        if file:match(pattern) then
            local path = folderPath.."/"..file
            folder[file] = readFile(path)
        end
    end
    return folder
end

-- Read multiple files from the folder
local folder = readFolder("folder", ".*%.hash$")

-- Main function
local function main()
    -- Print out the contents of single_file.txt
    print(fileString)
    print(fileByte)

    -- Retrieve some files from the folder
    print(folder["file1.hash"])
    print(folder["file2.hash"])
end

main()

To run this example, you’ll need to set up the folder structure and files:

$ mkdir -p folder
$ echo "hello lua" > folder/single_file.txt
$ echo "123" > folder/file1.hash
$ echo "456" > folder/file2.hash

Then run the Lua script:

$ lua embed-directive.lua
hello lua
hello lua
123
456

In this Lua version, we’ve implemented similar functionality to the Go embed directive:

1. We use the io library to read file contents.
2. The readFile function reads the contents of a single file.
3. The readFolder function reads multiple files from a folder that match a specific pattern. This requires the lfs (LuaFileSystem) library, which you may need to install separately.
4. We read the contents of single_file.txt into both a string and a byte representation (in Lua, strings can be used as byte arrays).
5. We read multiple files from the folder that end with .hash.
6. In the main function, we print out the contents of the files, similar to the Go example.

Note that Lua doesn’t have a built-in way to embed files at compile time like Go does. This script reads the files at runtime. For a more Go-like embed functionality, you would need to use a custom build process or a Lua compiler that supports embedding files.