Golang : Replace a parameter's value inside a configuration file example
Alright, putting this here for my own future reference. In this tutorial, we will explore how to read in a configuration(text) file, replace certain value of a parameter and write it back(update) into the file.
Basically, what this simple program does is to convert the entire configuration(text) file into a slice, scan for the parameter that we want to alter, update the parameter's value and write back to file.
Here you go!
package main
import (
"fmt"
"strings"
)
func main() {
input, err := ioutil.ReadFile(configFilename)
if err != nil {
log.Println(err)
}
// split into a slice
lines := strings.Split(string(input), "\n")
fmt.Println("before : ", lines)
// assuming that we want to change the value of thirdItem from 3 to 100
replacementText := "thirdItem = 100"
for i, line := range lines {
if equal := strings.Index(line, "thirdItem"); equal == 0 {
// update to the new value
lines[i] = replacementText
}
}
fmt.Println("after : ", lines)
// join back before writing into the file
linesBytes := []byte(strings.Join(lines, "\n"))
//the value will be UPDATED!!!
if err = ioutil.WriteFile(configFilename, linesBytes, 0666); err != nil {
log.Println(err)
}
}
You can play with a demo without modifying any file at https://play.golang.org/p/G8RKWdfh5hu
Hope this helps and happy coding!
References :
https://www.socketloop.com/references/golang-io-ioutil-writefile-function-example
https://www.socketloop.com/tutorials/golang-convert-string-to-byte-examples
See also : Golang : How to remove certain lines from a file
By Adam Ng(黃武俊)
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