filename-from-stdin.lua

#!/usr/bin/env lua

local type   = type
local print  = print
local pcall  = pcall
local select = select
local string = string
local io     = io

local string_format = string.format

local io_open  = io.open
local io_close = io.close
local io_read  = io.read
local io_write = io.write
local io_flush = io.flush

local _M = {}

--- Print text that's formatted using `string.format()`.
--- 
--- This function may fail.
---@param format string
---@param ... unknown
local function printf(format, ...)
	print(string_format(format, ...))
end

--- Check whether a given string is a valid filename, including whether the file
--- exists.
--- 
--- This function never fails.
---@param filename any
---@return boolean success
---@return string? filename_or_error
local function validate_filename(filename)
	local type_of_filename = type(filename)
	if type_of_filename ~= "string" then
		return false, string_format(
			"bad argument #1 to 'validate_filename' (string expected, got %s)",
			type_of_filename
		)
	end

	local file, error_message = io_open(filename, "r")

	if file == nil then
		return false, string_format(
			"could not open file %q in read mode: %s",
			filename,
			error_message or "unknown reason"
		)
	end

	local success, statuscode, exitcode = io_close(file)

	if not success then
		return false, string_format(
			"could not close file %q (exited with statuscode %q, exitcode %d)",
			filename,
			statuscode or "???",
			exitcode or -1
		)
	end

	return true, filename
end
_M.validate_filename = validate_filename

--- Try to read a filename from terminal input.
--- 
--- This function never fails.
---@return boolean success
---@return string? filename_or_error
local function try_read_filename()
	io_write("Enter a filename > ")
	io_flush()

	local success, input_or_error = pcall(io_read)

	if not success then
		return false, input_or_error
	end

	if input_or_error == nil then
		return false, "no input provided"
	end

	return validate_filename(input_or_error)
end
_M.try_read_filename = try_read_filename

--- The main entry point when running this script as a command.
--- 
--- This function never fails.
local function main()
	while true do
		local success, filename_or_error = try_read_filename()

		if success then
			printf("Found file %q!", filename_or_error)
			break
		end

		printf("Error: %s", filename_or_error)
	end
end

if select("#", ...) == 0 then
	main()
end

return _M