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Go String Functions

Go's standard library provides a powerful strings package for working with text. Here are the most common functions you'll use.

Basic Examples

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package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "test"

    // 1. Searching
    fmt.Println("Contains:  ", strings.Contains(s, "es"))  // true
    fmt.Println("Count:     ", strings.Count(s, "t"))     // 2
    fmt.Println("HasPrefix: ", strings.HasPrefix(s, "te")) // true
    fmt.Println("HasSuffix: ", strings.HasSuffix(s, "st")) // true
    fmt.Println("Index:     ", strings.Index(s, "e"))     // 1

    // 2. Joining and Splitting
    fmt.Println("Join:      ", strings.Join([]string{"a", "b"}, "-")) // a-b
    fmt.Println("Split:     ", strings.Split("a-b-c-d-e", "-"))       // [a b c d e]

    // 3. Transformation
    fmt.Println("Repeat:    ", strings.Repeat("a", 5))        // aaaaa
    fmt.Println("Replace:   ", strings.Replace("foo", "o", "0", -1)) // f00
    fmt.Println("Replace:   ", strings.Replace("foo", "o", "0", 1))  // f0o
    fmt.Println("ToLower:   ", strings.ToLower("TEST"))       // test
    fmt.Println("ToUpper:   ", strings.ToUpper("test"))       // TEST
}

Reference Table

Function What it does
Contains(s, substr) Returns true if substr is in s.
Count(s, substr) Returns how many times substr appears.
HasPrefix(s, prefix) Checks if s starts with prefix.
Index(s, substr) Returns the position of the first substr.
Join(slice, sep) Combines a slice of strings into one.
Split(s, sep) Breaks a string into a slice.
ToLower / ToUpper Changes the case.

Note on Efficiency

If you're building a long string piece by piece (like in a loop), don't use +. Instead, use strings.Builder. It's much faster because it doesn't create a new string every time you add to it.

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var b strings.Builder
for i := 0; i < 10; i++ {
    b.WriteString("word")
}
fmt.Println(b.String())