Golang Regular Expression Tutorial

Introduction

This lab demonstrates how to use regular expressions in Golang.

Regular Expressions

The lab requires you to complete the code to perform various regular expression-related tasks in Golang.

• Use the regexp package to perform regular expression-related tasks.
• Use MatchString to test whether a pattern matches a string.
• Use Compile to optimize a Regexp struct.
• Use MatchString to test a match like Compile.
• Use FindString to find the match for the regexp.
• Use FindStringIndex to find the first match and return the start and end indexes for the match instead of the matching text.
• Use FindStringSubmatch to return information for both p([a-z]+)ch and ([a-z]+).
• Use FindStringSubmatchIndex to return information about the indexes of matches and submatches.
• Use FindAllString to find all matches for a regexp.
• Use FindAllStringSubmatchIndex to apply to all matches in the input, not just the first.
• Use Match to test a match with []byte arguments and drop String from the function name.
• Use MustCompile to create global variables with regular expressions.
• Use ReplaceAllString to replace subsets of strings with other values.
• Use ReplaceAllFunc to transform matched text with a given function.

## For a complete reference on Go regular expressions check
## the [`regexp`](https://pkg.go.dev/regexp) package docs.

There is the full code below:

// Go offers built-in support for [regular expressions](https://en.wikipedia.org/wiki/Regular_expression).
// Here are some examples of  common regexp-related tasks
// in Go.

package main

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

    // This also finds the first match but returns the
    // start and end indexes for the match instead of the
    // matching text.
    fmt.Println("idx:", 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("all:", 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 global variables with regular
    // expressions you can use the `MustCompile` variation
    // of `Compile`. `MustCompile` panics instead of
    // returning an error, which makes it safer to use for
    // global variables.
    r = regexp.MustCompile("p([a-z]+)ch")
    fmt.Println("regexp:", 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))
}

Summary

This lab demonstrates how to use regular expressions in Golang to perform various tasks such as testing whether a pattern matches a string, finding the match for the regexp, and replacing subsets of strings with other values.