How to capitalize the first letter of a string

Question

I have a string like this

var sentence string = "the biggest ocean is the Pacific ocean"

I want to be able to capitalize the first letter t in the input string, so that the string becomes

"The biggest ocean is the Pacific ocean"

How to do that in Go?

I have tried using strings.Title and strings.ToTitle however they don't do what I want.

Answer 1

Get the first rune, title case that rune and reassemble the string:

sentence := "the biggest ocean is the Pacific ocean"
r, i := utf8.DecodeRuneInString(sentence)
sentence = string(unicode.ToTitle(r)) + sentence[i:]
fmt.Println(sentence)

Answer 2

Assuming that your input string is valid UTF-8 , this thread ( Golang - ToUpper() on a single byte? ) is close enough, though not quite a perfect duplicate. We can build on that to come to an acceptable solution using unicode.ToUpper on the first rune of the string.

    r := []rune(s)
    r[0] = unicode.ToUpper(r[0])
    s := string(r)

Or with a "clever" one-liner:

    s := string(append([]rune{unicode.ToUpper(r[0])}, r[1:]...))

Unlike strings, rune slices are not immutable, so you can replace the first rune with ToUpper , which will take care of non-ASCII and/or multi-byte code points that do have upper cases (eg Russian) and leave alone those that don't (eg Asian scripts)

NOTE: there is a difference between UPPER case and TITLE case, which is simply explained here . In short, digraph characters like DŽ will have different title case (Dž, only first grapheme capitalized) and upper cases (DŽ, both graphemes capitalized). If you actually need titlecase, use unicode.ToTitle .

NOTE 2: converting to/from string to []rune involves copying, because you get a mutable slice from an immutable string. Do profile your application if you expect to use it in performance-sensitive code.

Playground: https://go.dev/play/p/HpCBM7cRflZ

Answer 3

Here's a couple of ways of doing this

The first alters the bit pattern in the first byte of the sentence

The second calls a upper casing function on a string made of the first character of the sentence

Both make a new newsentence string as strings are immutable, they can't be altered

package main

import (
    "fmt"
    "strings"
)

func methodb() {
    var sentence = "the biggest ocean is the Pacific ocean"
    var b = []byte(sentence)
    b[0] = b[0] & 223
    var newsentence = string(b)
    fmt.Println(newsentence)
}

func methoda() {
    var sentence = "the biggest ocean is the Pacific ocean"
    var newsentence = fmt.Sprintf("%s%s", strings.ToUpper(string(sentence[0])), sentence[1:])
    fmt.Println(newsentence)
}

func main() {
    methoda()
    methodb()
}

Answer 4

The simplest way to achieve the desired result is to use strings.ToUpper() function. Refer

    var input string = "the biggest ocean is the Pacific ocean"
    res := strings.ToUpper(input[:1]) + input[1:]

    fmt.Println(res)

OR

You can try it on goplayground

Answer 5

I have simple solution for you.

Its a fork I have of someones project on Github

https://github.com/CleanMachine1/capitalise

To use it just run in a terminal:

go mod init MODULENAME
go get github.com/cleanmachine1/capitalise

then in your code you can use

package main

import ("github.com/cleanmachine1/capitalise")

func main(){
 sentence = capitalise.First(sentence)
}