Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
gu

Test String

Code Generator

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "(?<=^|[\\n;](?:[\\t ]*(?:\\w+ )?)?)export\\s*(?<modifiers>(?:\\s*declare|\\s*abstract|\\s*async)+)?\\s*(?<declaration>class|const +enum|const|enum|function\\*?|interface|let|namespace|type(?! *\\{)|var)\\s+(?<exports>(?:[$_\\p{ID_Start}][$\\u200C\\u200D\\p{ID_Continue}]*(?=[\\s=:;/(\\{])(?!.*?,))|(?:[\\w\\t\\n\\r .,:$'\"=-]+)|(?:[\\{[][\\w\\t\\n\\r .,:$'\"-]+[\\}\\]]))(?:\\s*=\\s*[$_\\p{ID_Start}][$\\u200C\\u200D\\p{ID_Continue}]*)?"; final String string = "export const CJS_SYNTAX_REGEX: RegExp = /pattern/gm;export const IGNORE_PATTERNS: string[] = [];\n" + "export declare const RESOLVE_EXTENSIONS: string[]\n" + "export enum Snack{}\n" + "export const enum Snack {}\n" + "export interface User {}\n" + "export class House {}\n" + "export declare abstract class House extends Building {}\n" + "export abstract class House {}\n" + "export async function run() {}\n" + "export async function* run() {}\n" + "export function foo() {}\n" + "export function* foo() {}\n" + "export const $foo = 42\n" + "export const $foo= 42\n" + "export namespace Foo {}\n" + "export type Foo = 'foo'\n" + "export let name1, name2/*, … */; // also var\n" + "export const name1 = 1, name2 = 2/*, … */; // also var, let\n" + "export function functionName() { /* … */ }\n" + "export class ClassName { /* … */ }\n" + "export function* generatorFunctionName() { /* … */ }\n" + "export const { name1, name2: bar } = o;\n" + "export const [ name1, name2 ] = array;\n\n" + "declare module 'module-name' {\n" + " export declare abstract class Building {}\n" + " export declare class House extends Building {}\n" + "}\n\n" + "\"export const $foo = 42\"\n\n" + "export default async function functionName() { /* … */ }\n" + "export default function functionName() { /* … */ }\n" + "export default function* generatorName() { /* … */ }\n" + "export default async function* generatorNameAsync() { /* … */ }\n" + "export default class ClassName { /* … */ }\n" + "export default abstract class ClassName { /* … */ }\n\n" + "export default function () { /* … */ }\n" + "export default async function () { /* … */ }\n" + "export default function* () { /* … */ }\n" + "export default async function* () { /* … */ }\n" + "export default class { /* … */ }\n\n" + "export default async () => {}\n" + "export default async arg => {}\n" + "export default () => {}\n" + "export default arg => {}\n" + "export default (arg) => {}\n\n" + "export default foo\n" + "export default foo;\n" + "export default 1 + 1;\n\n" + "// export const CJS_SYNTAX_REGEX\n\n" + "/**\n" + " * Resolvable file extensions.\n" + " *\n" + " * @example\n" + " * export const CJS_SYNTAX_REGEX\n" + " */\n\n" + "export type Foo = 'foo'"; final Pattern pattern = Pattern.compile(regex, Pattern.UNICODE_CASE); final Matcher matcher = pattern.matcher(string); while (matcher.find()) { System.out.println("Full match: " + matcher.group(0)); for (int i = 1; i <= matcher.groupCount(); i++) { System.out.println("Group " + i + ": " + matcher.group(i)); } } } }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html