Go by Example: Contains Substring

Go 1.23

Checking if a string exists inside another is done with `strings.Contains`. For prefixes and suffixes, use `HasPrefix` and `HasSuffix`.

Code

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "seafood"

    // 1. Contains (Substring check)
    // Checks if "foo" is anywhere inside "seafood".
    if strings.Contains(s, "foo") {
        fmt.Println("Found 'foo'")
    }

    // 2. HasPrefix (Starts with)
    // More efficient than Contains for checking the start.
    if strings.HasPrefix(s, "sea") {
        fmt.Println("Starts with 'sea'")
    }

    // 3. HasSuffix (Ends with)
    // Checks the end of the string.
    if strings.HasSuffix(s, "food") {
        fmt.Println("Ends with 'food'")
    }

    // 4. ContainsAny (Character check)
    // Checks if ANY of the characters "x", "y", or "z" are in s.
    if !strings.ContainsAny(s, "xyz") {
        fmt.Println("No x, y, or z found")
    }
}

Explanation

The strings.Contains function is the standard way to check for the presence of a substring. It performs a highly optimized search and returns a boolean. While simple, it is case-sensitive, so "Foo" will not be found in "seafood". For case-insensitive checks, you would typically use strings.Contains(strings.ToLower(s), "foo") or regular expressions.

When validating data formats, checking the beginning or end of a string is common. strings.HasPrefix and strings.HasSuffix are specialized functions for this. They are more readable and performant than using Contains or slicing strings manually. Additionally, strings.ContainsAny is useful for validating that a string does not contain forbidden characters, as it checks for the presence of any character from a provided set.

Contains: General purpose substring check.
HasPrefix/Suffix: Optimized for start/end checks.
ContainsAny: Checks for presence of specific characters.

Code Breakdown

13

Using 'strings.Contains'. This scans the string 's' for the substring "foo". It returns true immediately upon finding a match.

19

Using 'strings.HasPrefix'. This is faster than 'Contains' because it only checks the beginning of the string. It's great for checking URL schemes (http://) or file paths.

31

Using 'strings.ContainsAny'. This checks if 's' contains 'x' OR 'y' OR 'z'. It's useful for input validation (e.g., ensuring no special characters).

Samplebadu

Go by Example: Contains Substring

Code

Explanation

Code Breakdown