Regular Expressions 101

Save & Manage Regex

  • Current Version: 1
  • Save & Share
  • Community Library

Flavor

  • PCRE2 (PHP)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java
  • .NET 7.0 (C#)
  • Rust
  • PCRE (Legacy)
  • Regex Flavor Guide

Function

  • Match
  • Substitution
  • List
  • Unit Tests
Sponsors
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]
  • Character class intersection
    [\w&&[^\d]]
  • 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
Processing...

Test String

Code Generator

Language

Generated Code

import re regex = re.compile(r"^function (\w+)\(") test_str = ("function Date(Y, M, D, h, m, s, ms) { // 1397\n" " var length = arguments.length; // 1398\n" " var date; // 1399\n" " if (this instanceof NativeDate) { // 1400\n" " var seconds = s; // 1401\n" " var millis = ms; // 1402\n" " if (hasSafariSignedIntBug && length >= 7 && ms > maxSafeUnsigned32Bit) { // 1403\n" " // work around a Safari 8/9 bug where it treats the seconds as signed // 1404\n" " var msToShift = Math.floor(ms / maxSafeUnsigned32Bit) * maxSafeUnsigned32Bit; // 1405\n" " var sToShift = Math.floor(msToShift / 1e3); // 1406\n" " seconds += sToShift; // 1407\n" " millis -= sToShift * 1e3; // 1408\n" " } // 1409\n" " date = length === 1 && $String(Y) === Y ? // isString(Y) // 1410\n" " // We explicitly pass it through parse: // 1411\n" " new NativeDate(DateShim.parse(Y)) : // 1412\n" " // We have to manually make calls depending on argument // 1413\n" " // length here // 1414\n" " length >= 7 ? new NativeDate(Y, M, D, h, m, seconds, millis) : // 1415\n" " length >= 6 ? new NativeDate(Y, M, D, h, m, seconds) : // 1416\n" " length >= 5 ? new NativeDate(Y, M, D, h, m) : // 1417\n" " length >= 4 ? new NativeDate(Y, M, D, h) : // 1418\n" " length >= 3 ? new NativeDate(Y, M, D) : // 1419\n" " length >= 2 ? new NativeDate(Y, M) : // 1420\n" " length >= 1 ? new NativeDate(Y instanceof NativeDate ? +Y : Y) : // 1421\n" " new NativeDate(); // 1422\n" " } else { // 1423\n" " date = NativeDate.apply(this, arguments); // 1424\n" " } // 1425\n" " if (!isPrimitive(date)) { // 1426\n" " // Prevent mixups with unfixed Date object // 1427\n" " defineProperties(date, { constructor: DateShim }, true); // 1428\n" " } // 1429\n" " return date; // 1430\n" " }") match = regex.search(test_str) if match: print(f"Match was found at {match.start()}-{match.end()}: {match.group()}") for group_num, group in enumerate(match.groups(), start=1): print(f"Group {group_num} found at {match.start(group_num)}-{match.end(group_num)}: {group}")

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 Python, please visit: https://docs.python.org/3/library/re.html