How do you replace a character in Go using the Regexp package ReplaceAll function?

Question

I am not familiar with C-like syntaxes and would like to write code to find & replace, say, all 'A's to 'B's in a source string, say 'ABBA' with the Regexp package ReplaceAll or ReplaceAllString functions? How do I set up type Regexp, src and repl? Here's the ReplaceAll code snippet from the Go documentation:

// ReplaceAll returns a copy of src in which all matches for the Regexp
// have been replaced by repl.  No support is provided for expressions
// (e.g. \1 or $1) in the replacement text.
func (re *Regexp) ReplaceAll(src, repl []byte) []byte {
    lastMatchEnd := 0; // end position of the most recent match
    searchPos := 0;    // position where we next look for a match
    buf := new(bytes.Buffer);
    for searchPos <= len(src) {
        a := re.doExecute("", src, searchPos);
        if len(a) == 0 {
            break // no more matches
        }


    // Copy the unmatched characters before this match.
    buf.Write(src[lastMatchEnd:a[0]]);

    // Now insert a copy of the replacement string, but not for a
    // match of the empty string immediately after another match.
    // (Otherwise, we get double replacement for patterns that
    // match both empty and nonempty strings.)
    if a[1] > lastMatchEnd || a[0] == 0 {
        buf.Write(repl)
    }
    lastMatchEnd = a[1];

    // Advance past this match; always advance at least one character.
    _, width := utf8.DecodeRune(src[searchPos:len(src)]);
    if searchPos+width > a[1] {
        searchPos += width
    } else if searchPos+1 > a[1] {
        // This clause is only needed at the end of the input
        // string.  In that case, DecodeRuneInString returns width=0.
        searchPos++
    } else {
        searchPos = a[1]
    }
}

// Copy the unmatched characters after the last match.
buf.Write(src[lastMatchEnd:len(src)]);

return buf.Bytes();

}

Answer 1

This is a routine to do what you want:

package main
import ("fmt"; "regexp"; "os"; "strings";);
func main () {
    reg, error := regexp.Compile ("B");
    if error != nil {
        fmt.Printf ("Compile failed: %s", error.String ());
        os.Exit (1);
    }
    output := string (reg.ReplaceAll (strings.Bytes ("ABBA"),
                      strings.Bytes ("A")));
    fmt.Println (output);
}

Answer 2

Here is a small example. You can also find good examples in he Regexp test class

package main

import (
    "fmt"
    "regexp"
    "strings"
)

func main() {
    re, _ := regexp.Compile("e")
    input := "hello"
    replacement := "a"
    actual := string(re.ReplaceAll(strings.Bytes(input), strings.Bytes(replacement)))
    fmt.Printf("new pattern %s", actual)
}