ReplaceAllString

Sometimes we have a string that can be matched with a Regexp pattern, and we want to replace each match with another string. This can be done with ReplaceAllString.

ReplaceAllString is similar to other Go regexp methods, but it adds the replacement step after the matching step. We call MustCompile before using ReplaceAllString().

Example

Here we show that we can replace strings using a pattern with regexp. This is some sample code from a Go program that generates this website.

package main

import (
    "fmt"
    "regexp"
)

func main() {
    // Input string.
    input := "/programs/stage-perls/"

    // Change a string starting with "stage" into a string ending with "compress."
    re := regexp.MustCompile(`stage-([a-z]*)`)
    replacementResult := re.ReplaceAllString(input, "stage-$1-compress")

    // Before and after.
    fmt.Println(input)
    fmt.Println(replacementResult)
}
/programs/stage-perls/
/programs/stage-perls-compress/

ReplaceAllStringFunc

In some situations, we may want to have a way to test each match before deciding on its replacement. We can use ReplaceAllStringFunc for these cases.

package main

import (
    "fmt"
    "regexp"
)

func ReplaceExample(a string) string {
    // Change some strings that are matched.
    if a == "!" {
        return "."
    }
    return "_"
}

func main() {
    text := "hello, friends!"
    result := regexp.MustCompile(`\W`).ReplaceAllStringFunc(text, ReplaceExample)
    fmt.Println(result)
}
hello__friends.

With ReplaceAllString we have a way to perform more complex substring replacements. We can use patterns and even functions to determine what to replace and the replacement values.