This will encompass things that I find useful and end up looking up later when I haven't written go in a while.
Concepts
functionName vs FunctionName
A function that starts with a lowercase letter is only available within the package in which it's defined.
A function that start with an uppercase letter is available to any packages in your program.
Compile binary
go build
String Interpolation
var a string = "Hello"
var b string = "World"
c := fmt.Sprintf("%s %s!", a, b)
fmt.Println(c)
Debugging
Start debugger:
dlv debug
Set breakpoint on line 36 in main.go:
break main.go:36
Set breakpoint on line 8 in anotherGoFile.go:
break anotherGoFile.go:8
Debug program with command line arguments (after compiling)
dlv debug -- -a argument -b another_argument
Print contents of the b variable
print b
Restart the debugging process
r
Resources:
https://github.com/derekparker/delve/issues/178
https://www.youtube.com/watch?v=zgLjVD5ZSOc
Useful Functions
Remove empty strings trailing in a slice
func RemoveTrailingEmptyStringsInStringArray(sa []string) []string {
lastNonEmptyStringIndex := len(sa) - 1
for i := lastNonEmptyStringIndex; i >= 0; i-- {
if sa[i] == "" {
lastNonEmptyStringIndex--
} else {
break
}
}
return sa[0 : lastNonEmptyStringIndex+1]
}
Read an input file from a specified path
func readLines(filePath string) ([]string, error) {
b, err := ioutil.ReadFile(filePath)
if err != nil {
return nil, err
}
return RemoveTrailingEmptyStringsInStringArray(strings.Split(string(b), "\n")), nil
}
Compiling binaries
OSX 64-bit:
env GOOS=darwin GOARCH=amd64 go build -o osx
Linux 64-bit:
env GOOS=linux GOARCH=amd64 go build -o linux
Resources:
https://www.digitalocean.com/community/tutorials/how-to-build-go-executables-for-multiple-platforms-on-ubuntu-16-04
https://stackoverflow.com/questions/42706246/how-to-build-executable-with-name-other-than-golang-package
Return multiple values from function
You can natively return multiple values in go. Here's a basic function example (specifcally the declaration and return):
func greatFunc(param1 string, param2 string, param3 string) (bool, string) {
// body omitted
return true, returnString
Resource:
https://gobyexample.com/multiple-return-values
Multiline string
var payload = ` include myfile
}`
Resource:
https://play.golang.org/p/kcupXFwzgrZ
Comments
Normal
// comment
Block
/*
comment
*/
Convert byte array to string
s := string(byteArray)
Resource:
https://stackoverflow.com/questions/14230145/what-is-the-best-way-to-convert-byte-array-to-string
Nested directory creation
err := os.MkdirAll("/tmp/foo/bar", os.ModePerm)
Resource:
https://stackoverflow.com/questions/28448543/how-to-create-nested-directories-using-mkdir-in-golang
Convert int to str
import "strconv"
strconv.Itoa(123) // "123"
Resource: https://stackoverflow.com/questions/10105935/how-to-convert-an-int-value-to-string-in-go
Check if string contains another string
import (
"strings"
)
var var2 string = "bla"
output := strings.Contains("blablabla", var2)
fmt.Println(output) // true
Resource: https://stackoverflow.com/questions/45266784/go-test-string-contains-substring
Filepath operations
import "fmt"
import "path/filepath"
func main() {
t := "/etc/init.d/somefile"
fmt.Printf("base is %q dir is %q is it absolute? %v\n",
filepath.Base(t),
filepath.Dir(t),
filepath.IsAbs(t))
d, f := filepath.Split(t)
fmt.Printf("split returns file %q dir %q\n", f, d)
fmt.Printf("clean it up %q", filepath.Clean("a/b/c/../d//////../../f"))
}
If you need to return a filepath:
d := "/etc/bla/bla2/bla3/"
filepath.Clean(filepath.Join(d, "../")) // /etc/bla/bla2
Get the directory of a path
fmt.Println(filepath.Dir("/root/.ansible/site.yml"))
Playground: https://play.golang.org/p/nlcH1G3x5Vs
Get the last element of a path
base := filepath.Base("/home/dennis/IdeaProjects/Playground/hello.go")
fmt.Println("Base:", base)
# returns hello.go
Resource: https://ispycode.com/GO/Path-and-Filepath/Last-element-of-path
Read template file
The person that put this together is a hero (Gustavo Bittencourt).
package main
import (
"log"
"os"
"path"
"text/template"
)
type Command struct {
ClassName string
CmdName string
Cmd string
}
func main() {
command := Command{
ClassName: "my_cmd",
CmdName: "cmd",
Cmd: "curl target.com:8001/asdf",
}
t := template.New("puppetModule.tmpl")
t, err := t.ParseFiles(path.Join("templates", "puppetModule.tmpl"))
if err != nil {
log.Fatal("Parse: ", err)
}
err = t.Execute(os.Stdout, command)
if err != nil {
log.Fatal("Execute: ", err)
}
}
puppetModule.tmpl
class {{.ClassName}} {
exec { '{{.CmdName}}':
path => '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin',
command => '{{.Cmd}}'
}
}
Go get cert errors fix
Obviously, this is not ideal (observe the -insecure flag):
go get -u -v -insecure <target project>
From go help get:
-u: Look for updates to existing packages
-v: Verbose progress and debug output
Resource:
https://github.com/golang/go/issues/18519
Generate random int in a range
import (
"fmt"
"math/rand"
"time"
)
func randInt(min int, max int) int {
return min + rand.Intn(max-min)
}
func main() {
start := 1
finish := 6
rand.Seed(time.Now().UTC().UnixNano())
fmt.Printf("%v", rand.Intn(finish-start)+start)
}
Resources:
https://stackoverflow.com/questions/44659343/how-to-choose-a-random-number-from-the-range
https://golang.cafe/blog/golang-random-number-generator.html
Get lowercase version of string
import "strings"
strings.ToLower("Gopher")
Copy file
import (
"io/ioutil"
"log"
)
func CpFile(src string, dst string) {
input, err := ioutil.ReadFile(src)
if err != nil {
log.Println(err)
return
}
err = ioutil.WriteFile(dst, input, 0644)
if err != nil {
log.Println("Error creating", dst)
log.Println(err)
return
}
}
Resource:
https://opensource.com/article/18/6/copying-files-go
Determine OS being used
package main
import (
"fmt"
"runtime"
)
func main() {
if runtime.GOOS == "linux" {
fmt.Println("You are running on Linux")
} else if runtime.GOOS == "darwin" {
fmt.Println("You are running on OSX")
} else if runtime.GOOS == "windows" {
fmt.Println("You are running on Windows")
} else {
fmt.Println("Unsupported OS detected")
}
}
Playground:
https://play.golang.org/p/ULd8sMpy0dt
Resources:
https://golangcode.com/detect-if-code-is-running-on-windows-at-runtime/
Go get private repo
git config --global url."git@github.com:".insteadOf "https://github.com/"
Resource:
https://bialon.net/post/how-to-go-get-private-repos/
Get Working Directory
func Gwd() string {
dir, err := os.Getwd()
if err != nil {
log.Fatalln(err)
}
return dir
}
Resource:
https://gist.github.com/arxdsilva/4f73d6b89c9eac93d4ac887521121120
String to String Array
cmd := "puppetserver ca list --all"
strArr := strings.Fields(cmd)
fmt.Println(strArr[0])
// Will print: puppetserver
Resource:
https://stackoverflow.com/questions/13737745/split-a-string-on-whitespace-in-go
Get everything but first element of array
range Arr[1:]
Resource:
https://stackoverflow.com/questions/37429248/skip-first-element-of-an-array-in-golang
Convert string array to string
strings.Join(arr []string, seperator string) string
Resource:
https://stackoverflow.com/questions/41756412/golang-convert-type-string-to-string
Install a specific binary version
go get github.com/some/tool@v1.0.1
Resource:
https://stackoverflow.com/questions/53368187/go-modules-installing-go-tools
Unit Testing
Run tests without caching
As of 1.12, you can no longer use GOCACHE=off, i.e.
GOCACHE=off go test -v -race ./...
However, you can use -count=1. For example:
go test -count=1 -v -race ./...
Resources:
https://github.com/golang/go/issues/26809
https://github.com/golang/go/issues/22758
Unit test unexported functions
An unexported function aka a private function requires a little hack to write unit tests for. The steps are as follows:
- Create a
export_test.gofile in which you will create an exported variable that points to the unexported function. For example:
package <package in which the unexported function exists>
var Backup = backup
- Next, create your normal
_testfile and be sure to reference the exported variable you created inexport_test.go
Resource:
https://medium.com/@robiplus/golang-trick-export-for-test-aa16cbd7b8cd
Check if string is in a slice
func stringInSlice(s string, slice []string) bool {
for _, v := range slice {
if s == v {
return true
}
}
return false
}
Example usage:
if stringInSlice("bla", blaSlice) {
fmt.Println("Gotem!")
}
Playground: https://play.golang.org/p/NoucaeldZoO
Go Mod
Create new go.mod file:
go mod init
Add module requirements for all packages
go mod tidy
Resources:
https://blog.golang.org/migrating-to-go-modules
https://medium.com/@fonseka.live/getting-started-with-go-modules-b3dac652066d
Slice
A slice is essentially an array in Golang.
Convert bytes to a string
s := string([]byte{65, 66, 67, 226, 130, 172})
fmt.Println(s) // ABC€
Resource: https://yourbasic.org/golang/convert-string-to-byte-slice/
Output to file
m := "stuff to write in file"
err = ioutil.WriteFile("./file.txt", m, 0644)
if err != nil {
log.Fatalf("error: %v", err)
}
Resource: https://gobyexample.com/writing-files
Unmarshal yaml
Begin by using https://mengzhuo.github.io/yaml-to-go/ to create a struct for the yaml file, for example:
type ansible []struct {
Name string `yaml:"name"`
Hosts string `yaml:"hosts"`
Become bool `yaml:"become"`
Roles []string `yaml:"roles"`
}
Once you've done that, read the yaml file and unmarshal it into the struct:
b, err := ioutil.ReadFile("./ansible.yml")
if err != nil {
log.Fatal(err)
}
d := ansible{}
err = yaml.Unmarshal(b, &d)
if err != nil {
log.Fatal(err)
}
log.Printf("%v", d)
If you make modifications to the yaml, marshal it and write it back to the file:
d[0].Roles = append(d[0].Roles, "hello2")
log.Printf("%v", d)
m, err := yaml.Marshal(&d)
if err != nil {
log.Fatalf("error: %v", err)
}
err = ioutil.WriteFile("./ansible_modified.yml", m, 0644)
if err != nil {
log.Fatalf("error: %v", err)
}
Resources:
https://github.com/go-yaml/yaml
https://gist.github.com/ka2n/4457eacdb6c986624eb29cc02fe8d31c
https://play.golang.org/p/nYZCWIi2hxa
Multi line variable assignment
var data2 = `
---
- hosts: all
remote_user: root
roles:
- common
- hosts: lb_servers
remote_user: root
roles:
- lb-nginx
- hosts: backend_servers
remote_user: root
roles:
- tomcat
- hosts: memcached_servers
remote_user: root
roles:
- memcached
`
Resource: https://github.com/ansible/ansible-examples/blob/master/tomcat-memcached-failover/site.yml
Set
// Create new empty set
set := make(map[string]bool)
// Add new element to the set
set["bla"] = true
// Print the elements of the set
for k := range set {
fmt.Println(k)
}
// Add item to set if it's not already there
if !set["bla"] {
set["bla"] = true
}
Resources:
https://yourbasic.org/golang/implement-set/
https://play.golang.org/p/T2TR_Aib-H7
Regular expressions
Check if string matches regex
file := "ansible.cfg.old"
matched, _ := regexp.MatchString(`ansible.cfg$`, file)
// Return false
fmt.Println(matched)
Resources:
https://yourbasic.org/golang/regexp-cheat-sheet/
https://play.golang.org/p/UUqSQHCqMsZ
Check if string is valid hostname
This will match valid hostnames as per RFC 1123.
line := "hostname.example.com"
validHostname, _ := regexp.MatchString(`^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$`, line)
if validHostname {
fmt.Println(line)
}
Resources:
https://stackoverflow.com/questions/106179/regular-expression-to-match-dns-hostname-or-ip-address
https://play.golang.org/p/Mhckhn4jj3r
Print go representation of a value
This is very helpful if you're trying to do something like copying a big slice into the The Go Playground, or want to get a sense of how something looks in go.
fmt.Printf("%#v", bigSlice)
Resource: https://stackoverflow.com/questions/24489384/how-to-print-the-values-of-slices
Convert relative to absolute path
// Operating from /home/user/dir
absFilePath = ""
path, err := filepath.Abs(Cli.FilePath)
if err != nil {
log.Printf("Error getting absolute path from %s", path)
}
absFilePath = path