Command Line Flags in Lua

Here’s the translation of the Go code to Lua, along with explanations in Markdown format suitable for Hugo:

-- Lua doesn't have built-in command-line flag parsing, so we'll use a simple
-- custom implementation for this example.

local function parse_args(args)
    local parsed = {}
    for i = 1, #args do
        local arg = args[i]
        local key, value = arg:match("^%-%-([^=]+)=(.+)$")
        if key and value then
            parsed[key] = value
        elseif arg:sub(1, 2) == "--" then
            parsed[arg:sub(3)] = true
        else
            table.insert(parsed, arg)
        end
    end
    return parsed
end

-- Define default values for our flags
local flags = {
    word = "foo",
    numb = 42,
    fork = false,
    svar = "bar"
}

-- Parse command-line arguments
local args = parse_args(arg)

-- Update flags with parsed values
for k, v in pairs(args) do
    if flags[k] ~= nil then
        flags[k] = v
    end
end

-- Print the parsed flags and any remaining arguments
print("word:", flags.word)
print("numb:", flags.numb)
print("fork:", flags.fork)
print("svar:", flags.svar)
print("tail:", table.concat(args, " "))

This Lua script demonstrates a basic implementation of command-line flag parsing, similar to the original example. Here’s how it works:

1. We define a parse_args function that takes the command-line arguments and parses them into a table. It handles both --key=value style arguments and boolean flags like --fork.

2. We set up default values for our flags in the flags table.

3. We call parse_args(arg) to parse the command-line arguments. In Lua, arg is a global table containing the command-line arguments.

4. We update our flags table with any values provided in the command-line arguments.

5. Finally, we print out the values of all flags and any remaining arguments.

To use this script, you would save it as a .lua file and run it from the command line. For example:

$ lua command-line-flags.lua --word=opt --numb=7 --fork --svar=flag
word: opt
numb: 7
fork: true
svar: flag
tail:

Note that Lua doesn’t have a built-in package for handling command-line flags like Go’s flag package. This implementation is a simplified version and doesn’t include features like automatic help text generation or type checking. For more complex command-line parsing in Lua, you might want to use a third-party library.

Also, unlike Go, Lua doesn’t have a compilation step. You run Lua scripts directly with the Lua interpreter.

$ lua command-line-flags.lua --word=opt
word: opt
numb: 42
fork: false
svar: bar
tail:

This example demonstrates how you can achieve similar functionality to Go’s flag parsing in Lua, albeit with a more manual approach. The concepts of parsing command-line arguments and using default values remain the same, even though the implementation details differ.