Overview
what is regular expression?
A regular expression(regex or regexp) is a notation for describing sets of character strings.
use cases
- "find" or "replace" operations on strings
- Input validation
golang library
regexp
- standard library
- It's the syntax accepted by RE2.
syntax
| Metacharacter | Description |
|---|---|
| . | any character, possibly including newline |
| [xyz] | character class |
| [^xyz] | negated character class |
| \1 | backreference (NOT SUPPORTED) |
| A-Z | character range |
| x+ | one or more x |
e.g.
a.c -> "abc"
[a.c] -> "a", "." or "c"
[abc] -> "a", "b" or "c"
[^ab] -> matches any character other than "a" or "b"
[a-z0-9] -> matches from "a" to "z" and from "0" to "9"
Note that
👉 RE2 doesn't support '\'(backreferences) in order to guarantee linear-time execution.
👉 To match a metacharacter, escape it with a backslash: '\'+ matches a literal plus character. (In order to remove their special meaing, prefix those characters with '\')
👉 The difference between Double Quote(") and Backtick(`) in Golang.
double quote(") - backslash('\') is recognized as escape character.
back quote(') => backslash('\') has not special meaning.
practice
import "regexp"
// regexp.MatchString(`(.)\1\1+`, pw) <- not support
pw := "abcd1234"
match, err := regexp.MatchString(`[^A-Za-z0-9]`, pw)
tag := "varchar(20);unique"
reg := regexp.MustCompile(`varchar\([0-9]+\)`)
r := reg.FindStringSubmatch(tag)
// r[0] varchar(20)refrence
https://pkg.go.dev/regexp
https://github.com/google/re2/wiki/Syntax
