Replace substring in Golang
Replace substring with other substring.
Replace method included in strings package returns 1st argument whose substring specified as 2nd argument is replaced with substring specified as 3rd argument.
Replacing is performed times specified as 4th argument.
If 4th argument is smaller than 0, replacing with no limit.
replace_string.go 
package main

import (
	"fmt"
	"strings"
)

func main() {
	// Target string
	str := "dog cat dog"

	// Show original string
	fmt.Println(str)

	// Replace one dog to panda
	fmt.Println(strings.Replace(str, "dog", "panda", 1))

	// Replace two dogs to panda
	fmt.Println(strings.Replace(str, "dog", "panda", 2))

	// Replace no dog
	fmt.Println(strings.Replace(str, "dog", "panda", 0))

	// Replace dog to panda infinitely
	fmt.Println(strings.Replace(str, "dog", "panda", -1))
}
Result 
$ go run replace_string.go
dog cat dog
panda cat dog
panda cat panda
dog cat dog
panda cat panda