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🔤 strings — String manipulation functions

Provides functions for searching, splitting, replacing, and transforming strings. In Go, strings are immutable UTF-8 byte sequences. This package covers all common string operations without needing external libraries.

Import: import "strings" | Docs: pkg.go.dev/strings

📋 Functions, Types & Constants

Name	Signature / Value	Description
strings.Contains	func Contains(s, substr string) bool	Report if substr is within s
strings.ContainsAny	func ContainsAny(s, chars string) bool	Report if any Unicode code point in chars is in s
strings.Count	func Count(s, substr string) int	Count non-overlapping instances of substr in s
strings.HasPrefix	func HasPrefix(s, prefix string) bool	Report if s begins with prefix
strings.HasSuffix	func HasSuffix(s, suffix string) bool	Report if s ends with suffix
strings.Index	func Index(s, substr string) int	Return index of first instance of substr in s
strings.LastIndex	func LastIndex(s, substr string) int	Return index of last instance of substr in s
strings.Replace	func Replace(s, old, new string, n int) string	Replace first n occurrences of old with new
strings.ReplaceAll	func ReplaceAll(s, old, new string) string	Replace all occurrences of old with new
strings.Split	func Split(s, sep string) []string	Split s into substrings separated by sep
strings.SplitN	func SplitN(s, sep string, n int) []string	Split into at most n substrings
strings.Join	func Join(elems []string, sep string) string	Join elements with separator
strings.Fields	func Fields(s string) []string	Split on whitespace, discarding empty strings
strings.TrimSpace	func TrimSpace(s string) string	Trim leading and trailing whitespace
strings.Trim	func Trim(s, cutset string) string	Trim leading and trailing chars in cutset
strings.TrimLeft	func TrimLeft(s, cutset string) string	Trim leading chars in cutset
strings.TrimRight	func TrimRight(s, cutset string) string	Trim trailing chars in cutset
strings.TrimPrefix	func TrimPrefix(s, prefix string) string	Remove prefix from s if present
strings.TrimSuffix	func TrimSuffix(s, suffix string) string	Remove suffix from s if present
strings.ToUpper	func ToUpper(s string) string	Return uppercase copy of s
strings.ToLower	func ToLower(s string) string	Return lowercase copy of s
strings.Title	func Title(s string) string	Return title-cased copy of s
strings.EqualFold	func EqualFold(s, t string) bool	Case-insensitive comparison
strings.Repeat	func Repeat(s string, count int) string	Return count copies of s concatenated
strings.NewReader	func NewReader(s string) *Reader	Return a Reader that reads from s
strings.NewReplacer	func NewReplacer(oldnew ...string) *Replacer	Create multi-pair string replacer
strings.Builder	type Builder struct{}	Efficient string builder (use WriteString + String())
strings.Cut	func Cut(s, sep string) (before, after string, found bool)	Cut s around first instance of sep (Go 1.18+)

💡 Example Program

Save as main.go inside any directory and run with go run main.go. No extra packages to install — all standard library.

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "  Hello, Go World!  "

    fmt.Println(strings.TrimSpace(s))
    fmt.Println(strings.ToUpper(s))
    fmt.Println(strings.ToLower(s))
    fmt.Println(strings.Contains(s, "Go"))
    fmt.Println(strings.HasPrefix(strings.TrimSpace(s), "Hello"))
    fmt.Println(strings.Count(s, "l"))
    fmt.Println(strings.ReplaceAll(s, "Go", "Golang"))
    fmt.Println(strings.Index(s, "Go"))

    // Split and Join
    csv := "apple,banana,cherry,date"
    parts := strings.Split(csv, ",")
    fmt.Println(parts)
    fmt.Println(strings.Join(parts, " | "))

    // Fields — split on any whitespace
    words := strings.Fields("  foo   bar  baz  ")
    fmt.Println(words)

    // Cut — split around separator (Go 1.18+)
    before, after, found := strings.Cut("user@example.com", "@")
    fmt.Printf("before=%s  after=%s  found=%v\n", before, after, found)

    // Builder — efficient string construction
    var b strings.Builder
    for i := 0; i < 5; i++ {
        fmt.Fprintf(&b, "item%d ", i)
    }
    fmt.Println(b.String())

    // NewReplacer — multiple substitutions in one pass
    r := strings.NewReplacer("Go", "Golang", "World", "Universe")
    fmt.Println(r.Replace("Hello, Go World!"))
}
// go run main.go

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