Course outline

01 · Getting Started

02 · Variables, Types & Control Flow

03 · Functions & Composite Types

04 · Methods, Interfaces & Errors

05 · Packages, Modules & Concurrency Intro

06 · Your First Real Program

07 · Testing & Debugging in Go

08 · Capstone — Ship a Real Tool

Stage 1 · Code

Your First Real Program

Reading Input

Parse command-line arguments, read flags, and scan interactive input safely.

7 min readProgramming Foundations (Go)Code

os.Args

os.Args is a slice of strings containing the program name and all command-line arguments. os.Args[0] is always the executable name; arguments start at os.Args[1].

Goreading-os.args-directly.go

17 linesLn 1, Col 1Go

Write errors to `os.Stderr` (not Stdout) so they can be redirected separately. `os.Exit(1)` terminates immediately with a non-zero exit code, signalling failure to the shell.

The flag Package

The flag package parses named flags like -title "Buy milk". Flags can be booleans, integers, strings, or durations. flag.Parse() must be called before reading flag values.

Godefining-and-parsing-flags.go

25 linesLn 1, Col 1Go

`flag.String` returns a `*string` — dereference with `*title` to get the value. `flag.Usage()` prints the generated usage message. Call it before `os.Exit` when validation fails so users know what flags are available.

Subcommands with flag.FlagSet

flag.FlagSet creates an independent flag set for each subcommand. This lets add and list have different flags without interfering with each other.

Gosubcommand-routing-with-flagset.go

49 linesLn 1, Col 1Go

The router in `main` dispatches `os.Args[2:]` (everything after the subcommand) to the handler function. Each handler creates its own `FlagSet` and parses its own slice of arguments.

Reading stdin

bufio.Scanner reads stdin line by line without loading the whole input into memory. This is the correct approach for pipelines and interactive programs.

Goreading-lines-from-stdin.go

35 linesLn 1, Col 1Go

Always check `scanner.Err()` after the scan loop — it is non-nil only on actual I/O errors, not on EOF. An empty line is a clean termination sentinel for interactive input.

Mark this lesson complete to store local progress and unlock a cleaner resume path the next time you visit.