[go] Extracting substrings in Go

I'm trying to read an entire line from the console (including whitespace), then process it. Using bufio.ReadString, the newline character is read together with the input, so I came up with the following code to trim the newline character:

input,_:=src.ReadString('\n')
inputFmt:=input[0:len(input)-2]+"" //Need to manually add end of string

Is there a more idiomatic way to do this? That is, is there already a library that takes care of the ending null byte when extracting substrings for you?

(Yes, I know there is already a way to read a line without the newline character in go readline -> string but I'm looking more for elegant string manipulation.)

Go strings are not null terminated, and to remove the last char of a string you can simply do:

s = s[:len(s)-1]

WARNING: operating on strings alone will only work with ASCII and will count wrong when input is a non-ASCII UTF-8 encoded character, and will probably even corrupt characters since it cuts multibyte chars mid-sequence.

Here's a UTF-8-aware version:

// NOTE: this isn't multi-Unicode-codepoint aware, like specifying skintone or
//       gender of an emoji: https://unicode.org/emoji/charts/full-emoji-modifiers.html
func substr(input string, start int, length int) string {
    asRunes := []rune(input)
    
    if start >= len(asRunes) {
        return ""
    }
    
    if start+length > len(asRunes) {
        length = len(asRunes) - start
    }
    
    return string(asRunes[start : start+length])
}

To avoid a panic on a zero length input, wrap the truncate operation in an if

input, _ := src.ReadString('\n')
var inputFmt string
if len(input) > 0 {
    inputFmt = input[:len(input)-1]
}
// Do something with inputFmt

To get substring

1. find position of "sp"

2. cut string with array-logical

https://play.golang.org/p/0Redd_qiZM

This is the simple one to perform substring in Go

package main

import "fmt"

var p = fmt.Println

func main() {

  value := "address;bar"

  // Take substring from index 2 to length of string
  substring := value[2:len(value)]
  p(substring)

}

8 years later I stumbled upon this gem, and yet I don't believe OP's original question was really answered:

so I came up with the following code to trim the newline character

While the bufio.Reader type supports a ReadLine() method which both removes \r\n and \n it is meant as a low-level function which is awkward to use because repeated checks are necessary.

IMO an idiomatic way to remove whitespace is to use Golang's strings library:

input, _ = src.ReadString('\n')

// more specific to the problem of trailing newlines
actual = strings.TrimRight(input, "\r\n")

// or if you don't mind to trim leading and trailing whitespaces 
actual := strings.TrimSpace(input)

See this example in action in the Golang playground: https://play.golang.org/p/HrOWH0kl3Ww