Regular Expressions 101

Save & Manage Regex

  • Current Version: 14
  • 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
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
Processing...

Test String

Code Generator

Language

Generated Code

import re regex = re.compile(r"\b(127\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|0?10\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|172\.0?1[6-9]\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|172\.0?2[0-9]\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|172\.0?3[01]\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|192\.168\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|169\.254\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|::1|[fF][cCdD][0-9a-fA-F]{2}(?:[:][0-9a-fA-F]{0,4}){0,7}|[fF][eE][89aAbB][0-9a-fA-F](?:[:][0-9a-fA-F]{0,4}){0,7})(?:\/([789]|1?[0-9]{2}))?\b", flags=re.MULTILINE) test_str = ("# loopback\n" "127.0.0.0\n" "127.0.0.0000 # only three digits supported here\n\n" "# A\n" "10.0.0.1/10\n" "10.255.22.33\n\n" "# B\n" "172.17.100.155/32\n\n" "# C\n" "192.168.1.1\n" "192.168.1.255\n\n" "# IPv6\n" "fc00:833e:d648:f196:5c6c:1d9a:a14b:0d59\n" "fc01:67e5::6a66:34a7\n" "FC02:5fcf:e093:bb10:ce77:b5c9::/112\n" "fc03:49bd:b7c1:5685:fa0a:87e9::2/128\n" "fc04:::2 hmpf\n" "# Public IP addresses\n" "0de9:b022:883f:2c3c:7dba:a184:7576:4531\n" "04e4:e53b:0c2f:2990:27ad:0464:6dd3:b6b3\n" "0319:3b4a:546e:d480:4814:f885:3396:bba2\n" "5394:03f5:606f:273e:e343:d94a:610a:3f2e\n" "63cd:ad1f:7ffb:62c7:cc17:6e20:9b59:2f7d\n\n" "# More \"crap\"\n" "30.168.1.255.1\n" "127.1\n" "192.168.1.256\n" "-1.2.3.4\n" "1.1.1.1.\n" "3...3\n" "255.255.255.255\n" "0.0.0.0\n" "1.1.1.01\n" "192.99.16.30\n\n" "# decimal vs. octal mix\n" "172.032.33.33\n" "172.033.33.33\n\n" "# octal - not supported here\n" "0254.0021.0062.0041\n\n" "# link-local addresses IPv4\n" "169.254.1.0\n" "169.254.254.255\n\n" "# link-local addresses IPv6\n" "fe90:1234::/64\n" "feaf:ffff::/128\n" "febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff\n") matches = regex.finditer(test_str) for match_num, match in enumerate(matches, start=1): print(f"Match {match_num} 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