Golang : Skip or discard items of non-interest when iterating example

Problem:

You want to skip or discard items of non-interest when iterating. For example, skipping the commented lines with # sign in the /etc/passwd file.

 ##
 # User Database
 #
 # Note that this file is consulted directly only when the system is running
 # in single-user mode.  At other times this information is provided by
 # Open Directory.
 #
 # See the opendirectoryd(8) man page for additional information about
 # Open Directory.
 ##
 nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false
 root:*:0:0:System Administrator:/var/root:/bin/sh
 daemon:*:1:1:System Services:/var/root:/usr/bin/false

Solution:

Test each line(item) with strings.Index() function to see if the line starts with # sign. If the # sign is detected, skip or discard the item. This example reads the iterable items from a file; however, you can easily modify it to accommodates array or slice.

 package main

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

 func main() {
 file, err := os.Open("/etc/passwd")

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 defer file.Close()

 reader := bufio.NewReader(file)

 for {
 line, err := reader.ReadString('\n')

 // skip all line starting with #
 if equal := strings.Index(line, "#"); equal < 0 {
 fmt.Print(line)
 }

 // alternatively, only print line starting with #
 //if equal := strings.Index(line, "#"); equal >= 0 {
 // fmt.Print(line)
 // }

 if err == io.EOF {
 break
 }
 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 }

 }

Output:

 nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false
 root:*:0:0:System Administrator:/var/root:/bin/sh
 daemon:*:1:1:System Services:/var/root:/usr/bin/false

References:

https://www.socketloop.com/tutorials/golang-read-data-from-config-file-and-assign-to-variables

https://golang.org/pkg/strings/#Index