07-02_sorted_lines_verifying_out.lua

function readFile(inputFile)
    local openedFile = false
    if inputFile ~= nil then
        io.input(inputFile)
        openedFile = true
    end

    local lines = {}
    
    for line in io.lines() do
        lines[#lines+1] = line
    end

    if openedFile then
        io.input():close()
    end
    return lines
end

function sortLines(lines)
    table.sort(lines)
end

function writeOutput(sortedLines, outputFile)
    local openedFile = false
    if outputFile ~= nil then
        local f = io.open(outputFile, "r")
        if f ~= nil then
            f:close()
            io.write(string.format("Output file already '%s' exists. Overwrite? [y/n]\n", outputFile))
            stream = io.input(io.stdin)
            local confirmation = string.lower(io.read("l"))
            if confirmation == "n" then
                return
            elseif confirmation ~= "y" then
                io.write("Invalid option. Only 'y' or 'n' are accepted")
                return
            end
        end
        openedFile = true
    end

    io.output(outputFile)
    for _, line in ipairs(sortedLines) do
        io.write(line, "\n")
    end

    if openedFile then
        io.output():close()
    end
end

inputFile = arg[1]
outputFile = arg[2]

lines = readFile(inputFile)
sortLines(lines)
writeOutput(lines, outputFile)