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

/
/
gm

Test String

Code Generator

Generated Code

use strict; my $str = 'This still has a problem with FOUR+ character match \\b(?<!val\\s)(?<!var\\s)(?<!=)(?<!=\\s)(?<!\\.)([A-Z]{1,3}[0-9]*?)\\b \\b(?<!val\\s|var\\s|=|=\\s|\\.)([A-Z]+|[A-Z0-9]+)\\b \\b([A-Z0-9]{1,3})\\b(?![\\(;:])(?=[,\\)> ]) <[A-Z0-9]+>|\\([A-Z0-9]+\\) \\b([A-Z0-9]{1,3})\\b <in T, out R> : R { : R = (S, T, R) (S) -> S -> (S) [^a-z:\\s\\.\\,] <> :\\w+(?=,|>) //------------------- class IO<out A>(val fn: () -> A) { // blows the stack fun <B> map(g: (A) -> B): IO<B> = IO { g(this()) } fun <B> flatMap(g: (A) -> IO<B>): IO<B> = IO { g(this())() } operator fun invoke(): A = fn() companion object { val empty: IO<Unit> = IO {} operator fun <A> invoke(a: A): IO<A> = IO { a } } } // blows the stack fun <A, B> forever(ioa: IO<A>): IO<B> { val t: () -> IO<B> = { forever(ioa) } return ioa.flatMap { t() } } var count = 0 val program: IOU = IO { forever<String, String>(IO { "${count++} Repeating function" }) .flatMap { Console.println(it) } } //----------------------- class State<S, out T>(val runState: (S) -> Pair<S, T>) { fun <R> map(f: (T) -> R): State<S, R> = flatMap { t -> pure<S, R>(f(t)) } fun <P15, R> map(sx: State<S, P1>, f: (T, P1) -> R): State<STAB, R> = flatMap { t -> sx.map { x -> f(t, x) } } fun <R> flatMap(f: (T) -> State<S, R>): State<S, R> = State { s -> val (s1, t) = runState(s) f(t).runState(s1) } companion object { fun <S, T> pure(t: T): State<S, T> = State { s -> s to t } fun <S> get(): State<S, S> = State { s -> s to s } fun <S> set(newState: S): State<S, Unit> = State { _ -> newState to Unit } fun <S> modify(f: (S) -> S): State<S, Unit> = get<S>().flatMap { s: S -> set(f(s)).map { Unit } } } } //---------------- data class Book( val ISDN: String, val name: String, val pages: Int, val price: Price, val weight: Double, val year: Int, val author: String ) //------------------- fun <S, A> StateAlias<S, A>.map(f: (A) -> Boolean): StateAlias<S, Boolean> = { s -> val (s1, t) = this(s) when { f(s1) -> Pair(true, t) else -> Pair(false, t) } } fun <S, A, B> flatMap(): ((StateAlias<S, A>) -> (A)) -> ((A) -> (StateAlias<S, B>)) -> StateAlias<S, B> //-------------------- val dog = Dog(id = 0, name = "Doglin", furColour = FurColour.BLACK val cat: DOG = DOG //------------------- fun <T : Comparable<T>> sort(list: List<T>) fun <T> cloneWhenGreater(list: List<T>, threshold: T): List<T> where T : Comparable, T : Cloneable { return list.filter { it > threshold }.map { it.clone() } } //---------------------- enum class FurColour { BLACK, GREEN, PATCHED; } enum class Direction { NORTH, SOUTH, WEST, EAST } enum class Color(val rgb: Int) { RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF) } enum class ProtocolState { WAITING { override fun signal() = TALKING }, TALKING { override fun signal() = WAITING }; abstract fun signal(): ProtocolState }'; my $regex = qr/((?<==\h)\([A-Z][A-Z0-9_]+\b(?=[<:\;])|\b(?<!<)[A-Z][A-Z0-9_]+(?=[^>\)]))\b|\b((?<!=\s)(?<!\.)[A-Z]+\d*?(?![\(\;:])(?=[,\)>\s]))\b/mp; if ( $str =~ /$regex/g ) { print "Whole match is ${^MATCH} and its start/end positions can be obtained via \$-[0] and \$+[0]\n"; # print "Capture Group 1 is $1 and its start/end positions can be obtained via \$-[1] and \$+[1]\n"; # print "Capture Group 2 is $2 ... and so on\n"; } # ${^POSTMATCH} and ${^PREMATCH} are also available with the use of '/p' # Named capture groups can be called via $+{name}

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 Perl, please visit: http://perldoc.perl.org/perlre.html