Go by Example: Regular Expressions

Go offers built-in support for regular expressions. Here are some examples of common regexp-related tasks in Go.
	package main
	import "bytes" import "fmt" import "regexp"
	func main() {
This tests whether a pattern matches a string.	match, _ := regexp.MatchString("p([a-z]+)ch", "peach") fmt.Println(match)
Above we used a string pattern directly, but for other regexp tasks you’ll need to `Compile` an optimized `Regexp` struct.	r, _ := regexp.Compile("p([a-z]+)ch")
Many methods are available on these structs. Here’s a match test like we saw earlier.	fmt.Println(r.MatchString("peach"))
This finds the match for the regexp.	fmt.Println(r.FindString("peach punch"))
The also finds the first match but returns the start and end indexes for the match instead of the matching text.	fmt.Println(r.FindStringIndex("peach punch"))
The `Submatch` variants include information about both the whole-pattern matches and the submatches within those matches. For example this will return information for both `p([a-z]+)ch` and `([a-z]+)`.	fmt.Println(r.FindStringSubmatch("peach punch"))
Similarly this will return information about the indexes of matches and submatches.	fmt.Println(r.FindStringSubmatchIndex("peach punch"))
The `All` variants of these functions apply to all matches in the input, not just the first. For example to find all matches for a regexp.	fmt.Println(r.FindAllString("peach punch pinch", -1))
These `All` variants are available for the other functions we saw above as well.	fmt.Println(r.FindAllStringSubmatchIndex( "peach punch pinch", -1))
Providing a non-negative integer as the second argument to these functions will limit the number of matches.	fmt.Println(r.FindAllString("peach punch pinch", 2))
Our examples above had string arguments and used names like `MatchString`. We can also provide `[]byte` arguments and drop `String` from the function name.	fmt.Println(r.Match([]byte("peach")))
When creating constants with regular expressions you can use the `MustCompile` variation of `Compile`. A plain `Compile` won’t work for constants because it has 2 return values.	r = regexp.MustCompile("p([a-z]+)ch") fmt.Println(r)
The `regexp` package can also be used to replace subsets of strings with other values.	fmt.Println(r.ReplaceAllString("a peach", "<fruit>"))
The `Func` variant allows you to transform matched text with a given function.	in := []byte("a peach") out := r.ReplaceAllFunc(in, bytes.ToUpper) fmt.Println(string(out)) }

	$ go run regular-expressions.go true true peach [0 5] [peach ea] [0 5 1 3] [peach punch pinch] [[0 5 1 3] [6 11 7 9] [12 17 13 15]] [peach punch] true p([a-z]+)ch a <fruit> a PEACH
For a complete reference on Go regular expressions check the `regexp` package docs.

Previous example: String Formatting.

Next example: JSON.