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

%
%
mg

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"^\s*\S*\w*\W*(?<severity>\w)(?<time>\d{4}\s[^\s]*)\s+(?<pid>\d+)\s+(?<source>[^ \]]+)\](?<message>.*\n)" test_str = ("{\"log\":\"I1121 14:37:42.883962 1 serve.go:85] Serving securely on 0.0.0.0:6443\\n\",\"stream\":\"stderr\",\"time\":\"2017-11-21T14:37:42.902231562Z\"}\n" "{\"log\":\"I1121 14:37:42.885062 1 apiservice_controller.go:112] Starting APIServiceRegistrationController\\n\",\"stream\":\"stderr\",\"time\":\"2017-11-21T14:37:42.902266652Z\"}\n" "{\"log\":\"I1121 14:37:42.885079 1 cache.go:32] Waiting for caches to sync for APIServiceRegistrationController controller\\n\",\"stream\":\"stderr\",\"time\":\"2017-11-21T14:37:42.902269685Z\"}\n" "{\"log\":\"I1121 14:37:42.886031 1 available_controller.go:192] Starting AvailableConditionController\\n\",\"stream\":\"stderr\",\"time\":\"2017-11-21T14:37:42.902271525Z\"}\n" "{\"log\":\"I1121 14:37:42.886043 1 cache.go:32] Waiting for caches to sync for AvailableConditionController controller\\n\",\"stream\":\"stderr\",\"time\":\"2017-11-21T14:37:42.902273437Z\"}\n" " {\"log\":\"E0213 13:30:06.573154 1 cleaner.go:100] Error while attempting to clean CSR \"csr-4nzcx\": unable to delete CSR \\\\\\\"csr-4nzcx\\\\\\\": certificatesigningrequests.certificates.k8s.io \\\\\\\"csr-4nzcx\\\\\\\" is forbidden: User \\\\\\\"system:serviceaccount:kube-system:certificate-controller\\\\\\\" cannot delete certificatesigningrequests.certificates.k8s.io at the cluster scope\\\\n\\\",\\\"stream\\\":\\\"stderr\\\",\\\"time\\\":\\\"2018-02-13T13:30:06.575560335Z\\\"}\"\n" "\"log\": \"I0213 17:07:12.217422 1 trace.go:76] Trace[120533389]: \\\"Create /api/v1/namespaces/default/events\\\" (started: 2018-02-13 17:07:08.211886864 +0000 UTC m=+8.804410052) (total time: 4.005504088s):\\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