Find

With regexp we are often trying to find strings within a larger string. We use patterns (passed to MustCompile) to determine which values match.

To use Find, we must have byte slices. This is inconvenient in some programs. We can use a method like FindAllString instead, to operate directly on strings.

Find example

Here we use Find. We try to find a 3-digit sequence that begins with the value 2. The Find method returns the leftmost matching sequence as a byte slice.

package main

import (
    "fmt"
    "regexp"
)

func main() {
    // Match 3-digit values starting with 2.
    re := regexp.MustCompile("2\\d\\d")

    // Use find to get leftmost match.
    result := re.Find([]byte("123 124 125 205 211"))

    // Convert back to string and print it.
    fmt.Println(string(result))
}
205

FindAllString

This func finds multiple matches of a pattern within a string. It returns the values in a slice—we can loop over it with a for-loop.

package main

import (
    "fmt"
    "regexp"
)

func main() {
    // Match 3-char values starting with digit 1.
    re := regexp.MustCompile("1..")

    // Find and loop over all matching strings.
    results := re.FindAllString("123 124 125 200 211", -1)
    for i := range(results) {
        fmt.Println(results[i])
    }
}
123
124
125

With Find methods, we perform a search within the source string—the entire string is not matched as in MatchString(). We can test matches in a for-loop after the method call.