This will encompass things that I find useful and end up looking up later when I haven't written go in a while.
Concepts
A slice is essentially an array in Golang.
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
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
}
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]
}
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
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