Golang : Read data from config file and assign to variables

Usually a large program will need multiple parameters to function properly and the parameters will determine the behavior of the program. A good programmer will make his or her program to accept parameters from command line, environment or read from a file.

In this tutorial, we will learn how to read data from a plain text config file - simulating a program reading parameters from a file.

Here you go!

 package main

 import (
  "bufio"
  "fmt"
  "io"
  "os"
  "strings"
 )

 type Config map[string]string

 func ReadConfig(filename string) (Config, error) {
 // init with some bogus data
  config := Config{
 "port": "8888",
 "password": "abc123",
 "ip": "127.0.0.1",
  }
  if len(filename) == 0 {
 return config, nil
  }
  file, err := os.Open(filename)
  if err != nil {
 return nil, err
  }
  defer file.Close()
  
  reader := bufio.NewReader(file)
  
  for {
 line, err := reader.ReadString('\n')
 
 // check if the line has = sign
 // and process the line. Ignore the rest.
 if equal := strings.Index(line, "="); equal >= 0 {
 if key := strings.TrimSpace(line[:equal]); len(key) > 0 {
 value := ""
 if len(line) > equal {
 value = strings.TrimSpace(line[equal+1:])
 }
 // assign the config map
 config[key] = value
 }
 }
 if err == io.EOF {
 break
 }
 if err != nil {
 return nil, err
 }
  }
  return config, nil
 }

 func main() {
 // for this tutorial, we will hard code it to config.txt
  config, err := ReadConfig(`config.txt`)

  if err != nil {
 fmt.Println(err)
  }

  //fmt.Println("Config data dump :", config)

  // assign values from config file to variables
  ip := config["ip"]
  pass := config["password"]
  port := config["port"]

  fmt.Println("IP :", ip)
  fmt.Println("Port :", port)
  fmt.Println("Password :", pass)
 }

Reading a sample config.txt file :

 [profile manager]
 key=value
 password = sjssh31mmv
 ; a comment
 port = 8080
 ip = 123.456.789.321
 # another comment
 url=example.com
 file=
 # last comment

Sample output :

IP : 123.456.789.321

Port : 8080

Password : sjssh31mmv