part 4

print("Programming Environment")
print("Commands: 'run <file>', 'save <file>', 'load <file>', 'exit'")
while true do
    write("> ")
    local input = read()
    local command, arg = string.match(input, "^(%S+)%s*(.*)$")
    if command == "run" and arg then
        if fs.exists(arg) then
            local success, err = pcall(function() shell.run(arg) end)
            if not success then
                print("Error: " .. err)
                local log = fs.open("/error_log.txt", "a")
                log.writeLine("Error while running " .. arg .. ": " .. err)
                log.close()
            end
        else
            print("File not found.")
        end
    elseif command == "save" and arg then
        write("Enter your code. Type 'end' to finish.")
        local code = ""
        while true do
            local line = read()
            if line == "end" then break end
            code = code .. line .. "\n"
        end
        local file = fs.open(arg, "w")
        file.write(code)
        file.close()
        print("File saved as " .. arg)
    elseif command == "load" and arg then
        if fs.exists(arg) then
            local file = fs.open(arg, "r")
            print(file.readAll())
            file.close()
        else
            print("File not found.")
        end
    elseif command == "exit" then
        break
    else
        print("Invalid command.")
    end
end