Golang Cheat Sheet

Compile and Format

Format source code for proper syntax

go fmt src/code.go

Run a go program w/o compiling

go run src/code.go

generate a binary (will be placed in $GOPATH/bin)

cd src/project/
go install

run Golang documenation in your browser

go doc -http=:8080

open up browser, localhost:8080

Packages
example importing packages and using variables from each

$GOROOT/github.com/Joe/repoName/joe.go

cat $GOROOT/github.com/Joe/repoName/joe.go

package JoePkg
var MyName = "Joe"
var MyAge = 33

cat $GOROOT/github.com/YourName/repoName/main.go

package mainimport ( "fmt" "github.com/Joe/repoName/")func main() { fmt.Println(JoePkg.myName) fmt.Println(JoePkg.myAge)}

Slice (Dynamic Array)

like an array but can change size

s := []int{1,2,3}

>> [ 1 2 3 ]

append to slice

fmt.Println(append(s, 20, 21))
>> [ 1 2 3 20 21 ]

create empty slice of 3 elements

words := make([]string, 3)
words[0] = "hello"
words[1] = "there"

cars := []string{"buick", "honda", "chevy"}

get length of slice

fmt.Println(len(words))

append to slicewords = append(words, "sugar")

delete slice elements 2-4

z := []int{9, 8, 7, 6, 5, 3, 2, 1, 0}
fmt.Println(z)
>> [9 8 7 6 5 3 2 1 0]

z = append(z[:2], z[4:]...)
fmt.Println(z)>> [9 8 5 3 2 1 0]

copy contents from 1 slice to another

s1 := []int{1,2,3} >> creates a slice of integers [1 2 3]s2 := make([]int, 2) >> creates empty slice of 2 integers [0 0]

copy s1 > s2

copy(s2, s1)fmt.Println(s2) >>> [1 2] // will cut off any extra

Data Types

Constant

value never changes, can be number, bool, or string

const s string = "banana"

get type of data structure

import reflectmyVar := "blah"fmt.Println(reflect.TypeOf(myVar).String())

Types

int8 (-128 to 127)int16 (-32,768 to 32,767)int32 (2,147,483,648 to 2,147,483,647)int64 (-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807)uint8, 16, 32, 64float 32, 64

Structs (similar to Class)

type person struct { name string age int}

func main() { fmt.Println(person{"bob", 20}) ## {bob, 20} s := person{"joe",35} fmt.Println(s.name) ## joe}

Array

inflexible, can only declare an array size, but cant change size later

var a [5]intb := [5]int{1, 2, 3, 4, 5}fmt.Println("array is:", b)

Double array (matrix)

array := [# items][max size of each array]<type>{ {array}, {array}}

array := [2][4]int{{1,2,3,4}, {5,6,7}}

if Array is specified with size, and is provided w smaller size, Go will populate with zeros

array := [3][5]int{{1,2,3,4}, {5,6,7}}fmt.Println(array)>> [[1 2 3 4 0] [5 6 7 0 0] [0 0 0 0 0]]

Hashes / Dictionary (Map)

package mainimport "fmt"func main() { prices := make(map[string]float64) prices["OCKOPROG"] = 89.99 prices["ALBOÖMME"] = 129.99 prices["TRAALLÅ"] = 49.99 for key, value := range prices { fmt.Printf("Key: %s\tValue: %v\n", key, value) }}

Map - ie Dictionary or Hash

age := make(map[string]int)age["Joe"] = 28
age["Sarah"] = 32

delete a key

delete(age, "Joe")

Pointers

show memory address of a variable

s := "abc"
fmt.Println(&s)0xc0000a0220

Strings

print string

fmt.Println("Hello, world")

print value

fmt.Printf(variable)

print variable and string

fmt.Printf("the answer is:", variable)
fmt.Printf("%s\n", a)

get length of string

fmt.Println(len(variable))

package alias

package mainimport ( mongo "/lib/mongodb/db")

func main() { mongo.Get()

install dependency manager

apt install go-dep

dep init

TESTING

name Go file with underscore

_test.go

FILE HANDLING

open file for reading

file, err := os.Create("/tmp/file")if err != nil { panic(err)}fmt.Fprintln(file, number)

JSON

read in a struct, generate a pretty print JSON

import (  "encoding/json"  "fmt"  "net"  "os")
type OperatingSystem struct {  Kernel string `json:"kernel"`  KernelRelease string `json:"kernel release"`  KernelVersion string `json:"kernel version"`  LSBRelease string `json:"lsb release,omitempty"`}
func main() {  ret := OperatingSystem{  Kernel: "linux",  KernelRelease: "123",  KernelVersion: "6.3",  LSBRelease: "linux mint",}
data, _ := json.MarshalIndent(ret, "", " ")fmt.Println(string(data))

Logical Operators

&& = and

|| = or

! = not

sss

Conditionals

for loop

i := 1 for i <= 3 {
fmt.Println(i)
i = i + 1
}
for j := 7; j <= 9; j++ {
fmt.Println(j)
}
for { fmt.Println("loop")
break
}

if / Else

if num := 9; num < 0 {
fmt.Println(num, "is negative")
} else if num < 10 {
fmt.Println(num, "has 1 digit")
} else {
fmt.Println(num, "has multiple digits")
}

Switch Case

i := 2
fmt.Print("write ", i, " as ")

switch i {
case 1: fmt.Println("one")
case 2: fmt.Println("two"
case 3: fmt.Println("three")
}

Functions

regular func

func NAME(incoming_var TYPE) return_var TYPE { return var}func add(a, b int) int { return a + b} func main () { result := add(1, 2) fmt.Println("1+2 =", result)} ## 1+2 = 3

multiple-value return function

func SumAndProduct(A, B int) (added, multiplied int) { added = A+B multiplied = A*B return added, multiplied}

Goto

func myFunc() { i := 0 Here: // label ends with ":" fmt.Println(i) i++ goto Here //jump to label "Here"}

Parameters

package mainimport ( "flag" "fmt")var name = flag.String("name", "world", "some name")// var name, default value, description of paramfunc main() { flag.Parse() //turn params into vars fmt.Printf("hello %s", *name)}

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