Greeter Project

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What You’ll Build

• Accepts a name as a command-line argument
• Greets the user with their name
• Demonstrates variable declaration and assignment
• Uses both regular and short variable declarations

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What You’ll Learn

• Working with os.Args to read command-line arguments
• Declaring and assigning variables
• Using short variable declaration (:=)
• Multiple variable assignments
• Basic string formatting with fmt.Println

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Project Versions

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Version 1: Using var Declaration

package main

import (
	"fmt"
	"os"
)

func main() {
	var name string

	// assign a new value to the string variable
	name = os.Args[1]
	fmt.Println("Hello great", name, "!")

	// changes the name, declares the age with 85
	name, age := "gandalf", 85

	fmt.Println("My name is", name)
	fmt.Println("My age is", age)
	fmt.Println("BTW, you shall pass!")
}

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Version 2: Using Short Declaration

package main

import (
	"fmt"
	"os"
)

func main() {
	// assign a new value using short declaration
	name := os.Args[1]
	fmt.Println("Hello great", name, "!")

	// changes the name, declares the age with 85
	name, age := "gandalf", 85

	fmt.Println("My name is", name)
	fmt.Println("My age is", age)
	fmt.Println("BTW, you shall pass!")
}

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Running the Program

# Compile and run with an argument
go run main.go Alice

Hello great Alice !
My name is gandalf
My age is 85
BTW, you shall pass!

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Understanding os.Args

• os.Args[0] - Path to the running program
• os.Args[1] - First command-line argument
• os.Args[2] - Second command-line argument
• And so on…

// Print all arguments
fmt.Printf("%#v\n", os.Args)

// Get the first argument
fmt.Println("1st argument:", os.Args[1])

// Get the number of arguments
fmt.Println("Items inside os.Args:", len(os.Args))

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Key Concepts

// Declaration: Creates a variable
var name string

// Assignment: Gives it a value
name = "Alice"

// Short declaration: Does both at once
name := "Alice"

// Assign multiple variables at once
name, age := "gandalf", 85

// At least one variable must be new when using :=
// Here, 'age' is new, so we can redeclare 'name'

// Slices are zero-indexed
slice := []string{"first", "second", "third"}

slice[0] // "first"
slice[1] // "second"
slice[2] // "third"

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Practice Exercises

1. Count Arguments - Print how many arguments were passed
2. Print the Path - Display the program’s path (os.Args[0])
3. Greet More People - Accept multiple names and greet each one
4. Add Age - Accept both name and age as arguments
5. Format Output - Use fmt.Printf for better formatting

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Next Steps