Regular Expressions 101

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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"(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]" test_str = ("Valid domain name matching.\n" "Vote for it: http://stackoverflow.com/a/30007882/697313\n\n" "Sample text for testing:\n" "abcdefghijklmnopqrstuvwxyz.ABCDEFGHIJKLMNOPQRSTUVWXYZ\n" "0123456789 +-.,!@#$%^&*();\\\\/|<>\\\"\\'\n" "12345 -98.7 3.141 .6180 9,000 +42\n" "555.123.4567 +1-(800)-555-2468\n" "foodemo.net\n" "bar.ba.test.co.uk\n" "www.demo.com\n" "http://foo.co.uk/\n" "http://regexr.com/foo.html?q=bar\n" "g.com\n" "g-.com\n" "com.g\n" "-g.com\n" "xn--d1ai6ai.xn--p1ai\n" "xn-fsqu00a.xn-0zwm56d\n" "xn--stackoverflow.com\n" "stackoverflow.xn--com\n" "stackoverflow.co.uk\n" "google.com.au\n\n" "-0-0o.com\n" "0-0o_.com (underscore not allowed)\n" "a.net\n" "-a.dot\n" "0-0o.com\n" "0-oz.co.uk\n" "0-tension.com.br\n" "0-wh-ao14-0.com-com.net\n" "a-1234567890-1234567890-1234567890-1234567890-1234567890-1234-z.eu.us\n" "a-1234567890-1234567890-1234567890-1234567890-1234567890-12345-z.eu.us (too long)\n\n" "List of valid domain names:\n" "www.google.com\n" "google.com\n" "mkyong123.com\n" "mkyong-info.com\n" "sub.mkyong.com\n" "sub.mkyong-info.com\n" "mkyong.com.au\n" "g.co\n" "mkyong.t.t.co\n\n" "List of invalid domain names, and why:\n" "mkyong.t.t.c – Tld must between 2 and 6 long\n" "mkyong,com – Comma is not allow\n" "mkyong – No Tld\n" "mkyong.123 , Tld not allow digit (can easily fix for this)\n" ".com – Must start with [A-Za-z0-9]\n" "mkyong.com/users – No Tld\n" "-mkyong.com – Cannot begin with a hyphen -\n" "mkyong-.com – Cannot end with a hyphen -\n" "sub.-mkyong.com – Cannot begin with a hyphen -\n" "sub.mkyong-.com – Cannot end with a hyphen -\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