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

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"^((?:[A-Za-z0-9!#$%&'*+\-\/=?^_`{|}~]|(?<=^|\.)\"|\"(?=$|\.|@)|(?<=\".*)[ .](?=.*\")|(?<!\.)\.){1,64})(@)((?:[A-Za-z0-9.\-])*(?:[A-Za-z0-9])\.(?:[A-Za-z0-9]){2,})$" test_str = ("Valid email addresses\n\n" "simple@example.com\n\n" "very.common@example.com\n\n" "disposable.style.email.with+symbol@example.com\n\n" "other.email-with-hyphen@example.com\n\n" "fully-qualified-domain@example.com\n\n" "user.name+tag+sorting@example.com\n" "(may go to user.name@example.com inbox depending on mail server)\n\n" "x@example.com\n" "(one-letter local-part)\n\n" "example-indeed@strange-example.com\n\n" "example@s.example\n" "(see the List of Internet top-level domains)\n\n" "\" \"@example.org\n" "(space between the quotes)\n\n" "\"john..doe\"@example.org\n" "(quoted double dot)\n\n" "=============================================================\n" "Invalid email addresses\n\n" "Abc.example.com\n" "(no @ character)\n\n" "A@b@c@example.com\n" "(only one @ is allowed outside quotation marks)\n\n" "a\"b(c)d,e:f;g<h>i[j\\k]l@example.com\n" "(none of the special characters in this local-part are allowed outside quotation marks)\n\n" "just\"not\"right@example.com\n" "(quoted strings must be dot separated or the only element making up the local-part)\n\n" "this is\"not\\allowed@example.com\n" "(spaces, quotes, and backslashes may only exist when within quoted strings and preceded by a backslash)\n\n" "this\\ still\\\"not\\\\allowed@example.com\n" "(even if escaped (preceded by a backslash), spaces, quotes, and backslashes must still be contained by quotes)\n\n" "1234567890123456789012345678901234567890123456789012345678901234+x@example.com\n" "(local part is longer than 64 characters)") 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