How to Use strings.HasPrefix in Go: Simple Guide

In Go, use strings.HasPrefix to check if a string starts with a specific prefix. It returns true if the string begins with the prefix, otherwise false. Import the strings package to use this function.

Syntax

The strings.HasPrefix function takes two arguments: the full string and the prefix string. It returns a boolean value indicating if the full string starts with the prefix.

• strings.HasPrefix(s, prefix string) bool
• s: The string to check.
• prefix: The prefix to look for at the start of s.
• Returns true if s starts with prefix, otherwise false.

go

package main

import (
	"fmt"
	"strings"
)

func main() {
	s := "golang programming"
	prefix := "go"
	result := strings.HasPrefix(s, prefix)
	fmt.Println(result) // true
}

Output

true

Example

This example shows how to use strings.HasPrefix to check different prefixes in a string and print the results.

go

package main

import (
	"fmt"
	"strings"
)

func main() {
	text := "hello world"

	fmt.Println(strings.HasPrefix(text, "he"))    // true
	fmt.Println(strings.HasPrefix(text, "hello")) // true
	fmt.Println(strings.HasPrefix(text, "world")) // false
	fmt.Println(strings.HasPrefix(text, ""))      // true (empty prefix always matches)
}

Output

true
true
false
true

Common Pitfalls

Some common mistakes when using strings.HasPrefix include:

• Forgetting to import the strings package.
• Confusing HasPrefix with case-insensitive checks (it is case-sensitive).
• Expecting it to check anywhere in the string instead of only at the start.
• Using nil or empty strings incorrectly.

Always remember strings.HasPrefix is case-sensitive and only checks the start of the string.

go

package main

import (
	"fmt"
	"strings"
)

func main() {
	text := "GoLang"

	// Wrong: case-insensitive check (this returns false)
	fmt.Println(strings.HasPrefix(text, "go"))

	// Right: exact case match
	fmt.Println(strings.HasPrefix(text, "Go"))
}

Output

false
true

Quick Reference

Function	Description	Returns
strings.HasPrefix(s, prefix string)	Checks if string s starts with prefix	bool (true or false)
Case sensitivity	The check is case-sensitive	N/A
Empty prefix	Always returns true if prefix is empty	true
Import	Requires importing the strings package	N/A

Key Takeaways

Use strings.HasPrefix to check if a string starts with a specific prefix in Go.

Remember that HasPrefix is case-sensitive and only checks the start of the string.

Always import the strings package before using HasPrefix.

An empty prefix always returns true when checked with HasPrefix.

Use exact case matches to get correct results with HasPrefix.