46_regular_expressions.go

package gobyexample

import (
	"bytes"
	"fmt"
	"regexp"
)

// RegexpDemo - demonstrates usage of regular expressions
func RegexpDemo() {
	// test whether a pattern matches a string
	match, _ := regexp.MatchString("p([a-z]+)ch", "peach")
	fmt.Println(match)

	// for other regexp tasks we 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"))

	// This 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
	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 methods apply to all matches in the input
	fmt.Println(r.FindAllString("peach punch pinch", -1))

	// These All variants are available for the other methods we saw above
	// as well
	fmt.Println(r.FindAllStringSubmatchIndex("peach punch pinch", -1))

	// Providing a non-negative integer as the second argument to these
	// methods 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` variant
	// of `Compile`. A plain `Compile` won't work for constants because it has 2 return values.
	r = regexp.MustCompile("p([a-z]+)ch")

	// 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 within a given function
	in := []byte("a peach")
	out := r.ReplaceAllFunc(in, bytes.ToUpper)
	fmt.Println(string(out))
}