How to Replace Substrings in Go Using `strings.Replace`

Key Takeaways

The strings.Replace function allows replacing substrings in a case-sensitive manner.
Setting n to -1 ensures all occurrences are replaced.
strings.NewReplacer enables multiple substring replacements efficiently.

In Go programming, the strings package provides the Replace function to substitute occurrences of a specified substring within a string. The function signature is:

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

Where:

s is the original string.
old is the substring to be replaced.
new is the substring to replace old.
n specifies the number of non-overlapping instances to replace; if n is less than 0, all occurrences are replaced.

Usage Examples:

package main

import (
    "fmt"
    "strings"
)

func main() {
    original := "Hello, World! Hello, Golang!"

    // Replace all occurrences
    result := strings.Replace(original, "Hello", "Hi", -1)
    fmt.Println(result) // Output: Hi, World! Hi, Golang!

    // Replace the first occurrence
    result = strings.Replace(original, "Hello", "Hi", 1)
    fmt.Println(result) // Output: Hi, World! Hello, Golang!

    // Replace the first two occurrences
    result = strings.Replace(original, "Hello", "Hi", 2)
    fmt.Println(result) // Output: Hi, World! Hi, Golang!
}

Case Sensitivity:

The Replace function is case-sensitive. For example:

package main

import (
    "fmt"
    "strings"
)

func main() {
    original := "Hello, World! HELLO, Golang!"

    // Attempt to replace "hello" (lowercase)
    result := strings.Replace(original, "hello", "Hi", -1)
    fmt.Println(result) // Output: Hello, World! HELLO, Golang!
}

In this case, "hello" does not match "Hello" or "HELLO", so no replacements occur.

Replacing Multiple Substrings:

For multiple replacements, the strings package offers the Replacer type:

package main

import (
    "fmt"
    "strings"
)

func main() {
    original := "Hello, World! Hello, Golang!"

    replacer := strings.NewReplacer("Hello", "Hi", "World", "Earth")
    result := replacer.Replace(original)
    fmt.Println(result) // Output: Hi, Earth! Hi, Golang!
}