How to Replace Substrings in a String in Go

In Go, you can replace parts of a string using the strings.Replace function from the strings package. It takes the original string, the substring to replace, the replacement string, and the number of replacements to make. Use -1 to replace all occurrences.

Syntax

The strings.Replace function has this syntax:

• func Replace(s, old, new string, n int) string

Where:

• s is the original string.
• old is the substring you want to replace.
• new is the string to replace old with.
• n is the number of replacements to make. Use -1 to replace all occurrences.

go

package main

import (
	"fmt"
	"strings"
)

func main() {
	result := strings.Replace("hello world", "world", "Go", 1)
	fmt.Println(result)
}

Output

hello Go

Example

This example shows how to replace all occurrences of a substring in a string using strings.Replace. It replaces "cat" with "dog" everywhere in the text.

go

package main

import (
	"fmt"
	"strings"
)

func main() {
	text := "the cat sat on the cat mat"
	newText := strings.Replace(text, "cat", "dog", -1)
	fmt.Println(newText)
}

Output

the dog sat on the dog mat

Common Pitfalls

One common mistake is forgetting that strings in Go are immutable, so strings.Replace returns a new string and does not change the original. Another is using n incorrectly; setting it to 1 replaces only the first occurrence, not all.

Also, replacing an empty string "" can lead to unexpected results.

go

package main

import (
	"fmt"
	"strings"
)

func main() {
	original := "hello world"
	// Wrong: expecting original to change
	strings.Replace(original, "world", "Go", 1)
	fmt.Println(original) // prints "hello world"

	// Right: assign the result
	newStr := strings.Replace(original, "world", "Go", 1)
	fmt.Println(newStr) // prints "hello Go"
}

Output

hello world
hello Go

Quick Reference

Parameter	Description
s	Original string to search in
old	Substring to find and replace
new	Substring to replace with
n	Number of replacements (-1 means all)

Key Takeaways

Use strings.Replace to create a new string with replacements; original string stays unchanged.

Set n to -1 to replace all occurrences of the substring.

Always assign the result of strings.Replace to a variable to keep changes.

Replacing an empty string "" can cause unexpected behavior, so avoid it.

Import the strings package to use strings.Replace.