Golang Cheatsheet

Installation & Setup

Install Go: Download & Extract

Download and install Go from the official website.

# Download from https://golang.org/dl/
# Linux/macOS - extract to /usr/local
sudo tar -C /usr/local -xzf go1.21.5.linux-amd64.tar.gz
# Add to PATH in ~/.bashrc or ~/.zshrc
export PATH=$PATH:/usr/local/go/bin
# Verify installation
go version

Package Manager: Using Homebrew (macOS)

Install Go using Homebrew on macOS.

# Install Go with Homebrew
brew install go
# Verify installation
go version
go env GOPATH

Windows Installation

Install Go on Windows systems.

# Download .msi installer from https://golang.org/dl/
# Run installer and follow prompts
# Verify in Command Prompt
go version
echo %GOPATH%

Workspace Setup: go mod init

Initialize a new Go module and workspace.

# Create new directory and initialize module
mkdir my-go-project
cd my-go-project
go mod init my-go-project
# Create main.go
echo 'package main
import "fmt"
func main() {
    fmt.Println("Hello, World!")
}' > main.go
# Run the program
go run main.go

Environment Variables

Important Go environment variables.

# View all Go environment variables
go env
# Key variables
go env GOROOT    # Go installation directory
go env GOPATH    # Workspace directory
go env GOOS      # Operating system
go env GOARCH    # Architecture

IDE Setup: VS Code

Configure VS Code for Go development.

# Install Go extension in VS Code
# Ctrl+Shift+P -> Go: Install/Update Tools
# Key features enabled:
# - Syntax highlighting
# - IntelliSense
# - Debugging
# - Testing integration

Basic Syntax & Types

Package & Imports

Every Go file begins with a package declaration and imports.

package main
import (
    "fmt"
    "strings"
    "time"
)
// Single import
import "os"

Variables & Constants

Declare and initialize variables and constants.

// Variable declarations
var name string = "Go"
var age int = 15
var isOpen bool
// Short declaration
name := "Golang"
count := 42
// Constants
const Pi = 3.14159
const Message = "Hello, Go!"

Basic Data Types

Fundamental types available in Go.

// Numeric types
var i int = 42
var f float64 = 3.14
var c complex64 = 1 + 2i
// Text types
var s string = "Hello"
var r rune = 'A'
// Boolean
var b bool = true

Control Flow

Conditionals: if / else / switch

Control program flow with conditional statements.

// If statements
if age >= 18 {
    fmt.Println("Adult")
} else if age >= 13 {
    fmt.Println("Teenager")
} else {
    fmt.Println("Child")
}
// Switch statements
switch day {
case "Monday":
    fmt.Println("Start of work week")
case "Friday":
    fmt.Println("TGIF")
default:
    fmt.Println("Regular day")
}

Loops: for / range

Iterate using various loop constructs.

// Traditional for loop
for i := 0; i < 10; i++ {
    fmt.Println(i)
}
// While-style loop
for condition {
    // loop body
}
// Infinite loop
for {
    // break when needed
}

Range Iteration

Iterate over slices, arrays, maps, and strings.

// Iterate over slice
numbers := []int{1, 2, 3, 4, 5}
for index, value := range numbers {
    fmt.Printf("Index: %d, Value: %d\n", index, value)
}
// Iterate over map
colors := map[string]string{"red": "#FF0000", "green": "#00FF00"}
for key, value := range colors {
    fmt.Printf("%s: %s\n", key, value)
}
// Iterate over string
for i, char := range "Hello" {
    fmt.Printf("%d: %c\n", i, char)
}

Control Statements: break / continue

Control loop execution flow.

// Break out of loop
for i := 0; i < 10; i++ {
    if i == 5 {
        break
    }
    fmt.Println(i)
}
// Skip current iteration
for i := 0; i < 5; i++ {
    if i == 2 {
        continue
    }
    fmt.Println(i)
}

Functions

Function Declaration: func

Define functions with parameters and return values.

// Basic function
func greet(name string) {
    fmt.Printf("Hello, %s!\n", name)
}
// Function with return value
func add(a, b int) int {
    return a + b
}
// Multiple return values
func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, errors.New("division by zero")
    }
    return a / b, nil
}

Named Returns & Variadic Functions

Advanced function features and patterns.

// Named return values
func split(sum int) (x, y int) {
    x = sum * 4 / 9
    y = sum - x
    return // naked return
}
// Variadic function
func sum(nums ...int) int {
    total := 0
    for _, num := range nums {
        total += num
    }
    return total
}
// Usage
result := sum(1, 2, 3, 4, 5)

Function Types & Closures

Functions as first-class citizens in Go.

// Function as variable
var multiply func(int, int) int
multiply = func(a, b int) int {
    return a * b
}
// Anonymous function
square := func(x int) int {
    return x * x
}
// Closure
func counter() func() int {
    count := 0
    return func() int {
        count++
        return count
    }
}
// Usage
c := counter()
fmt.Println(c()) // 1
fmt.Println(c()) // 2

Defer Statement

Defer execution of functions until surrounding function returns.

func processFile(filename string) {
    file, err := os.Open(filename)
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close() // Executed when function returns

    // Process file contents
    // file.Close() will be called automatically
}

Data Structures

Arrays & Slices

Fixed and dynamic sequences of elements.

// Arrays (fixed size)
var arr [5]int = [5]int{1, 2, 3, 4, 5}
shortArr := [3]string{"a", "b", "c"}
// Slices (dynamic)
var slice []int
slice = append(slice, 1, 2, 3)
// Make slice with capacity
numbers := make([]int, 5, 10) // length 5, capacity 10
// Slice operations
slice2 := slice[1:3]  // [2, 3]
copy(slice2, slice)   // Copy elements

Maps

Key-value pairs for efficient lookups.

// Map declaration and initialization
var m map[string]int
m = make(map[string]int)
// Short declaration
ages := map[string]int{
    "Alice": 30,
    "Bob":   25,
    "Carol": 35,
}
// Map operations
ages["David"] = 40        // Add/update
delete(ages, "Bob")       // Delete
age, exists := ages["Alice"] // Check existence

Structs

Group related data together with custom types.

// Struct definition
type Person struct {
    Name    string
    Age     int
    Email   string
}
// Create struct instances
p1 := Person{
    Name:  "Alice",
    Age:   30,
    Email: "alice@example.com",
}
p2 := Person{"Bob", 25, "bob@example.com"}
// Access fields
fmt.Println(p1.Name)
p1.Age = 31

Pointers

Reference memory addresses of variables.

// Pointer declaration
var p *int
num := 42
p = &num  // Address of num
// Dereferencing
fmt.Println(*p) // Value at address (42)
*p = 100        // Change value through pointer
// Pointers with structs
person := &Person{Name: "Alice", Age: 30}
person.Age = 31  // Automatic dereferencing

Methods & Interfaces

Methods

Attach functionality to custom types.

type Rectangle struct {
    Width, Height float64
}
// Method with receiver
func (r Rectangle) Area() float64 {
    return r.Width * r.Height
}
// Pointer receiver (can modify)
func (r *Rectangle) Scale(factor float64) {
    r.Width *= factor
    r.Height *= factor
}
// Usage
rect := Rectangle{Width: 10, Height: 5}
fmt.Println(rect.Area()) // 50
rect.Scale(2)            // Modifies rect

Interfaces

Define contracts that types must satisfy.

// Interface definition
type Shape interface {
    Area() float64
    Perimeter() float64
}
// Implement interface for Rectangle
func (r Rectangle) Perimeter() float64 {
    return 2 * (r.Width + r.Height)
}
// Rectangle now implements Shape interface
func printShapeInfo(s Shape) {
    fmt.Printf("Area: %.2f, Perimeter: %.2f\n",
               s.Area(), s.Perimeter())
}

Empty Interface & Type Assertions

Work with values of unknown types.

// Empty interface can hold any value
var i interface{}
i = 42
i = "hello"
i = []int{1, 2, 3}
// Type assertion
str, ok := i.(string)
if ok {
    fmt.Printf("String value: %s\n", str)
}
// Type switch
switch v := i.(type) {
case int:
    fmt.Printf("Integer: %d\n", v)
case string:
    fmt.Printf("String: %s\n", v)
default:
    fmt.Printf("Unknown type: %T\n", v)
}

Embedding

Compose types by embedding other types.

type Person struct {
    Name string
    Age  int
}
type Employee struct {
    Person    // Embedded struct
    Company   string
    Salary    float64
}
// Usage
emp := Employee{
    Person:  Person{Name: "Alice", Age: 30},
    Company: "TechCorp",
    Salary:  75000,
}
// Access embedded fields directly
fmt.Println(emp.Name) // "Alice"

Error Handling

Basic Error Handling

Use the built-in error interface for error handling.

import "errors"
// Function that returns an error
func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, errors.New("division by zero")
    }
    return a / b, nil
}
// Error checking
result, err := divide(10, 2)
if err != nil {
    log.Fatal(err)
}
fmt.Printf("Result: %.2f\n", result)

Custom Errors

Create custom error types for specific error conditions.

// Custom error type
type ValidationError struct {
    Field   string
    Message string
}
func (e ValidationError) Error() string {
    return fmt.Sprintf("validation error in %s: %s",
                       e.Field, e.Message)
}
// Function using custom error
func validateAge(age int) error {
    if age < 0 {
        return ValidationError{
            Field:   "age",
            Message: "must be non-negative",
        }
    }
    return nil
}

Error Wrapping

Add context to errors while preserving the original error.

import "fmt"
// Wrap an error with additional context
func processFile(filename string) error {
    file, err := os.Open(filename)
    if err != nil {
        return fmt.Errorf("failed to open file %s: %w",
                          filename, err)
    }
    defer file.Close()

    // Process file...
    return nil
}
// Unwrap errors
err := processFile("missing.txt")
if err != nil {
    var pathErr *os.PathError
    if errors.As(err, &pathErr) {
        fmt.Println("Path error:", pathErr)
    }
}

Panic & Recovery

Handle exceptional situations with panic and recover.

// Function that might panic
func riskyOperation() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Recovered from panic:", r)
        }
    }()

    // This will cause a panic
    panic("something went wrong!")
}
// Usage
riskyOperation() // Program continues after panic

Concurrency

Goroutines

Lightweight threads managed by Go runtime.

import "time"
// Simple goroutine
func sayHello() {
    fmt.Println("Hello from goroutine!")
}
func main() {
    // Start goroutine
    go sayHello()

    // Anonymous goroutine
    go func() {
        fmt.Println("Anonymous goroutine")
    }()

    // Wait for goroutines to finish
    time.Sleep(time.Second)
}

Channels

Communication between goroutines using channels.

// Create channel
ch := make(chan int)
// Buffered channel
buffered := make(chan string, 3)
// Send and receive
go func() {
    ch <- 42  // Send value
}()
value := <-ch  // Receive value
// Close channel
close(ch)

Channel Patterns

Common patterns for channel communication.

// Worker pattern
func worker(id int, jobs <-chan int, results chan<- int) {
    for job := range jobs {
        fmt.Printf("Worker %d processing job %d\n", id, job)
        results <- job * 2
    }
}
// Fan-out pattern
jobs := make(chan int, 100)
results := make(chan int, 100)
// Start workers
for w := 1; w <= 3; w++ {
    go worker(w, jobs, results)
}
// Send jobs
for j := 1; j <= 5; j++ {
    jobs <- j
}
close(jobs)

Select Statement

Handle multiple channel operations simultaneously.

func main() {
    ch1 := make(chan string)
    ch2 := make(chan string)

    go func() {
        time.Sleep(time.Second)
        ch1 <- "from ch1"
    }()

    go func() {
        time.Sleep(2 * time.Second)
        ch2 <- "from ch2"
    }()

    // Select first available channel
    select {
    case msg1 := <-ch1:
        fmt.Println(msg1)
    case msg2 := <-ch2:
        fmt.Println(msg2)
    case <-time.After(3 * time.Second):
        fmt.Println("timeout")
    }
}

File I/O & JSON

File Operations

Read and write files using various methods.

import (
    "io/ioutil"
    "os"
)
// Read entire file
data, err := ioutil.ReadFile("file.txt")
if err != nil {
    log.Fatal(err)
}
content := string(data)
// Write to file
text := "Hello, World!"
err = ioutil.WriteFile("output.txt", []byte(text), 0644)
// Open file with more control
file, err := os.Open("data.txt")
if err != nil {
    log.Fatal(err)
}
defer file.Close()

CSV Handling

Read and write CSV files.

import (
    "encoding/csv"
    "os"
)
// Read CSV
file, _ := os.Open("data.csv")
defer file.Close()
reader := csv.NewReader(file)
records, _ := reader.ReadAll()
// Write CSV
file, _ = os.Create("output.csv")
defer file.Close()
writer := csv.NewWriter(file)
defer writer.Flush()
writer.Write([]string{"Name", "Age", "City"})
writer.Write([]string{"Alice", "30", "NYC"})

JSON Processing

Encode and decode JSON data.

import "encoding/json"
// Struct for JSON mapping
type Person struct {
    Name  string `json:"name"`
    Age   int    `json:"age"`
    Email string `json:"email,omitempty"`
}
// Marshal (Go to JSON)
person := Person{Name: "Alice", Age: 30}
jsonData, err := json.Marshal(person)
if err != nil {
    log.Fatal(err)
}
// Unmarshal (JSON to Go)
var p Person
err = json.Unmarshal(jsonData, &p)

HTTP Requests

Make HTTP requests and handle responses.

import "net/http"
// GET request
resp, err := http.Get("https://api.github.com/users/octocat")
if err != nil {
    log.Fatal(err)
}
defer resp.Body.Close()
body, _ := ioutil.ReadAll(resp.Body)
// POST request with JSON
jsonData := []byte(`{"name":"Alice","age":30}`)
resp, err = http.Post("https://api.example.com/users",
                      "application/json",
                      bytes.NewBuffer(jsonData))

Testing

Unit Testing: go test

Write and run tests using Go’s testing framework.

// math.go
package main
func Add(a, b int) int {
    return a + b
}
// math_test.go
package main
import "testing"
func TestAdd(t *testing.T) {
    result := Add(2, 3)
    expected := 5

    if result != expected {
        t.Errorf("Add(2, 3) = %d; want %d", result, expected)
    }
}
// Run tests
// go test
// go test -v (verbose)

Table-Driven Tests

Test multiple cases efficiently.

func TestAddMultiple(t *testing.T) {
    tests := []struct {
        name     string
        a, b     int
        expected int
    }{
        {"positive numbers", 2, 3, 5},
        {"with zero", 0, 5, 5},
        {"negative numbers", -1, -2, -3},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            result := Add(tt.a, tt.b)
            if result != tt.expected {
                t.Errorf("got %d, want %d", result, tt.expected)
            }
        })
    }
}

Benchmarking

Measure performance of functions.

func BenchmarkAdd(b *testing.B) {
    for i := 0; i < b.N; i++ {
        Add(2, 3)
    }
}
// Run benchmarks
// go test -bench=.
// go test -bench=BenchmarkAdd -benchmem

Example Tests

Create executable examples that serve as documentation.

import "fmt"
func ExampleAdd() {
    result := Add(2, 3)
    fmt.Printf("2 + 3 = %d", result)
    // Output: 2 + 3 = 5
}
func ExampleAdd_negative() {
    result := Add(-1, -2)
    fmt.Printf("(-1) + (-2) = %d", result)
    // Output: (-1) + (-2) = -3
}
// Run examples
// go test -run Example

Go Modules & Packages

Module Management

Initialize and manage Go modules for dependency management.

# Initialize new module
go mod init github.com/username/project
# Add dependencies
go get github.com/gorilla/mux
go get -u github.com/gin-gonic/gin  # Update to latest
# Remove unused dependencies
go mod tidy
# Download dependencies
go mod download
# Vendor dependencies locally
go mod vendor

go.mod File

Understanding the module definition file.

module github.com/username/myproject
go 1.21
require (
    github.com/gorilla/mux v1.8.0
    github.com/stretchr/testify v1.8.4
)
require (
    github.com/davecgh/go-spew v1.1.1 // indirect
    github.com/pmezard/go-difflib v1.0.0 // indirect
)

Creating Packages

Structure code into reusable packages.

// Package structure
// myproject/
//   ├── go.mod
//   ├── main.go
//   └── utils/
//       ├── math.go
//       └── string.go
// utils/math.go
package utils
// Exported function (starts with capital letter)
func Add(a, b int) int {
    return a + b
}
// Private function (starts with lowercase)
func multiply(a, b int) int {
    return a * b
}
// main.go
package main
import (
    "fmt"
    "github.com/username/myproject/utils"
)
func main() {
    result := utils.Add(5, 3)
    fmt.Println(result)
}

Common Go Commands

Essential commands for Go development.

# Run Go program
go run main.go
# Build executable
go build
go build -o myapp  # Custom name
# Install binary to GOPATH/bin
go install
# Format code
go fmt ./...
# Vet code for issues
go vet ./...
# Clean build cache
go clean -cache

Relevant Links

• Linux Cheatsheet
• Shell Cheatsheet
• DevOps Cheatsheet
• Docker Cheatsheet
• Kubernetes Cheatsheet
• Python Cheatsheet
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• Java Cheatsheet