strings.ToUpper() / ToLower() / TrimSpace()

import "strings"

// Converts to uppercase.
upper := strings.ToUpper(s)

// Converts to lowercase.
lower := strings.ToLower(s)

// Converts to title case (capitalizes the first letter of each word).
title := strings.Title(s) // Deprecated. Use golang.org/x/text/cases instead.

// Removes leading and trailing whitespace.
trimmed := strings.TrimSpace(s)

// Removes leading and trailing characters found in the cutset.
trimmed := strings.Trim(s, cutset)

// Removes leading characters only.
trimmed := strings.TrimLeft(s, cutset)

// Removes trailing characters only.
trimmed := strings.TrimRight(s, cutset)

// Removes a leading substring (exact match).
trimmed := strings.TrimPrefix(s, prefix)

// Removes a trailing substring (exact match).
trimmed := strings.TrimSuffix(s, suffix)

package main

import (
    "fmt"
    "strings"
)

func main() {
    // ToUpper / ToLower: case conversion
    s := "Hello, Go!"
    fmt.Println("ToUpper:", strings.ToUpper(s))
    fmt.Println("ToLower:", strings.ToLower(s))

    // Case-insensitive comparison
    a, b := "Go", "go"
    fmt.Println("Case-insensitive equal:", strings.ToLower(a) == strings.ToLower(b))

    fmt.Println()

    // TrimSpace: removes leading and trailing spaces and newlines.
    padded := "   Hello, World!   \n"
    fmt.Printf("Original: %q\n", padded)
    fmt.Printf("After TrimSpace: %q\n", strings.TrimSpace(padded))

    fmt.Println()

    // Trim: removes specified characters from both ends.
    s2 := "***Go Language***"
    fmt.Println("Trim('*'):", strings.Trim(s2, "*"))

    s3 := "---Hello---"
    fmt.Println("TrimLeft('-'):", strings.TrimLeft(s3, "-"))
    fmt.Println("TrimRight('-'):", strings.TrimRight(s3, "-"))

    fmt.Println()

    // TrimPrefix / TrimSuffix: removes a specific string from either end.
    url := "https://example.com"
    fmt.Println("TrimPrefix:", strings.TrimPrefix(url, "https://"))

    filename := "document.pdf"
    fmt.Println("TrimSuffix:", strings.TrimSuffix(filename, ".pdf"))

    fmt.Println()

    // Repeat: repeats a string.
    separator := strings.Repeat("=", 20)
    fmt.Println(separator)
    fmt.Println("Go Dictionary")
    fmt.Println(separator)
}

strings.TrimSpace() is one of the most commonly used functions for sanitizing user input. Use it to strip extra spaces and newlines from form values or configuration file entries. Note that the cutset in strings.Trim() is a set of individual characters, not a substring. To remove a specific substring, use strings.TrimPrefix() or strings.TrimSuffix() instead.

The cutset in strings.Trim(s, cutset) is a set of characters to remove, not a substring. For example, strings.Trim("---hello---", "---") removes the character "-", not the sequence "---". To remove a multi-character sequence, you need a different approach.

For string searching, see strings.Contains(). For conversions between strings and numbers, see strconv.Atoi() / Itoa().