Reading Command-Line Arguments
Parse argv with an allocator.
Reading Command-Line Arguments is a free Zig Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Zig Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why Arguments Matter
A real CLI tool reacts to what the user types after its name. Those words are the command-line arguments, and reading them is step one. 🛠️
Zig Hands You Nothing Hidden
Other languages give you a magic argv variable. Zig stays explicit: you ask the std.process namespace for the arguments yourself.
const std = @import("std");Arguments Need an Allocator
Decoding arguments may allocate memory, so Zig asks you for an allocator up front. No allocation happens behind your back.
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
const a = gpa.allocator();argsAlloc Gives a Slice
Call std.process.argsAlloc with your allocator. It returns a slice of strings, one per argument, that you fully own.
const args = try std.process.argsAlloc(a);Free What You Allocated
Because you own that slice, you must release it with argsFree. A defer right after the call keeps cleanup automatic.
defer std.process.argsFree(a, args);The First Argument Is the Program
By convention args[0] is the path to your own program, not user input. The real values you care about start at index 1.
const program = args[0];Count How Many You Got
The slice carries its own length, so args.len tells you how many arguments arrived. You check it before reaching for any index.
if (args.len < 2) return error.MissingArgument;Loop Over the Inputs
Iterate the user values by slicing past the program name. A for loop over args[1..] visits each argument in order.
for (args[1..]) |arg| {
std.debug.print("{s}\n", .{arg});
}Each Argument Is Bytes
Every argument is a []const u8, a slice of bytes. Comparing or parsing one is just normal Zig string work from here.
if (std.mem.eql(u8, arg, "--help")) {}Turn Text into Numbers
Arguments arrive as text. To get a number, parse it with std.fmt.parseInt, which fails clearly if the text is not a valid integer.
const n = try std.fmt.parseInt(i32, args[1], 10);An Iterator Alternative
Prefer streaming? std.process.argsWithAllocator gives an iterator you advance with next(), handy when you process arguments one at a time.
var it = try std.process.argsWithAllocator(a);
defer it.deinit();Quick Check
Think about what sits at the front of the arguments slice.
Recap
You read arguments with argsAlloc, freed them with argsFree, skipped args[0], and parsed text into values. Your CLI now hears its user. 🎯
Frequently asked questions
Is the “Reading Command-Line Arguments” lesson free?
Yes — the full text of “Reading Command-Line Arguments” is free to read here on the web, and the Zig Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Zig Academy course, upgrade to CoddyKit PRO.
What will I learn in “Reading Command-Line Arguments”?
Parse argv with an allocator. You practise Zig Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Zig Academy?
No prior experience is required. Zig Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Reading Command-Line Arguments” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Zig Academy lesson?
Yes. Every Zig Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Reading Command-Line Arguments
- Reading Files and stdin
- Writing Output and Exit Codes
- Package and Release the Binary