Regular Expressions 101

Save & Share

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java 8
  • .NET 7.0 (C#)
  • Rust
  • Regex Flavor Guide

Function

  • Match
  • Substitution
  • List
  • Unit Tests

Tools

Sponsors
There are currently no sponsors. Become a sponsor today!
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

/
/
gm

Test String

Code Generator

Language

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"(?:<[^>]*>)?(accessed(?:\s*\:?\s*| on ))((?:[0-2]?[0-9]?|30|31)(?:st|nd|rd|th)?)(?:<\/[^>]*>)?([\.\-\/ ])(Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|June?|July?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|Nov(?:ember)?|Dec(?:ember)?|[1-9]|1[012])([\.\-\/ ])(?:<[^>]*>)?(20\d{2})(?:<\/[^>]*>)?" test_str = ("<note>accessed 13</note> March <year>2022</year>\n" "<note>accessed 13th</note> March <year>2022</year>\n" " <note>accessed 8</note> April <year>2022</year>.\n" "accessed 21st February 2020\n" "accessed 32 Febr 2022\n" "accessed 32 February 2022\n" "accessed 30 February 202\n" "accessed 30 January 2022\n" "accessed 30 Jan 2022\n" "accessed 30 February 2022\n" "accessed 30 Feb 2022\n" "accessed: 30 March 2022\n" "accessed on 30 Mar 2022\n" "accessed 30 April 2022\n" "accessed 30 Apr 2022\n" "accessed 30 May 2022\n" "accessed 30 June 2022\n" "accessed 30 Jun 2022\n" "accessed 30 July 2022\n" "accessed 30 Jul 2022\n" "accessed 30 August 2022\n" "accessed 30 Aug 2022\n" "accessed 30 September 2022\n" "accessed 30 Sep 2022\n" "accessed 30 October 2022\n" "accessed 30 Oct 2022\n" "accessed 30 November 2022\n" "accessed 30 Nov 2022\n" "accessed 30 December 2022\n" "accessed 30 Dec 2022\n\n" "accessed on 30.12.2022\n" "accessed on 30.13.2022\n" "accessed on 34.12.2022\n" "accessed on 30.12.2023\n" "accessed on 30.15.2022\n" "accessed on 01.12.2022\n" "accessed on 41.12.2092\n\n" "accessed on 30-12-2022\n" "accessed on 30-13-2022\n" "accessed on 34-12-2022\n" "accessed :30-12-2023\n" "accessed :30-15-2022\n" "accessed :01-12-2022\n" "accessed :41-12-2092\n\n" "accessed : 30/12/2022\n" "accessed : 30/13/2022\n" "accessed :34/12/2022\n" "accessed :30/12/2023\n" "accessed : 30/15/2022\n" "accessed 01/12/2022\n" "accessed 41/12/2092\n\n\n\n\n\n\n\n") matches = re.finditer(regex, test_str, re.MULTILINE) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

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