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
  • Match everything enclosed
    (?:...)
  • Capture everything enclosed
    (...)
  • 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

/
/
g

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"<p>(\s*)(<a(.*)>)?(\s*)(https?:\/\/)?(w{3}\.)?(youtube\.com|youtu\.be)\/(watch\?v=|embed\/)?([A-Za-z0-9-_]{11})(\S*)(\s*)(<\/a>)?(\s*)<\/p>" test_str = ("No protocol:\n\n" "<p>youtube.com/watch?v=dQw4w9WgXcQ</p>\n" "<p>www.youtube.com/watch?v=dQw4w9WgXcQ</p>\n\n" "HTTP or HTTPS:\n\n" "<p>http://youtube.com/watch?v=dQw4w9WgXcQ</p>\n" "<p>http://www.youtube.com/watch?v=dQw4w9WgXcQ</p>\n" "<p>https://youtube.com/watch?v=dQw4w9WgXcQ</p>\n" "<p>https://www.youtube.com/watch?v=dQw4w9WgXcQ</p>\n\n" "With or without “www”\n\n" "<p>https://youtube.com/watch?v=dQw4w9WgXcQ</p>\n" "<p>https://www.youtube.com/watch?v=dQw4w9WgXcQ</p>\n\n" "Youtu.be short links\n" "<p>youtu.be/LQaehcfXvK0</p>\n" "<p>https://youtu.be/LQaehcfXvK0</p>\n\n" "Embed Urls:\n" "<p>http://www.youtube.com/embed/dQw4w9WgXcQ</p>\n\n" "URLs with extra parameters:\n" "<p>https://www.youtube.com/watch?v=LQaehcfXvK0&feature=youtu.be</p>\n" "<p>https://www.youtube.com/watch?v=dQw4w9WgXcQ&list=RDdQw4w9WgXcQ&start_radio=1&t=1</p>\n\n" "This URL won’t actually work on YouTube, but it works here, which is somewhat odd? And yet doesn't seem harmful.\n" "<p>youtu.be/embed/dQw4w9WgXcQ</p>\n\n" "Paragraph tags on separate lines with arbitrary whitespace:\n\n" "<p>\n" " www.youtube.com/embed/u8pCsfT1gDU\n" "</p>\n\n" "<p>\n" " https://youtube.com/watch?v=dQw4w9WgXcQ\n" "</p>\n" "<p>\n" " http://www.youtube.com/embed/dQw4w9WgXcQ\n" "</p>\n\n" " <p>\n" " youtube.com/watch?v=dQw4w9WgXcQ\n\n" "</p>\n\n" "Paragraph tags with any other text in them, besides the URL:\n\n" "<p>This shouldn’t work: https://youtube.com/watch?v=dQw4w9WgXcQ</p>\n" "<p>https://youtube.com/watch?v=dQw4w9WgXcQ nor this</p>\n" "<p>\n" "https://youtube.com/watch?v=dQw4w9WgXcQ also not this\n\n" "</p>\n\n\n" "Paragraph tags with links added by markdown-it:\n\n" "<p><a href=\"https://www.youtube.com/watch?v=dQw4w9WgXcQ\">https://www.youtube.com/watch?v=dQw4w9WgXcQ</a></p>\n\n" "<p>\n" " <a href=\"https://www.youtube.com/watch?v=dQw4w9WgXcQ?something\" class=\"something\" id=\"whatever\">\n" " youtube.com/watch?v=dQw4w9WgXcQ?foo=bar&whatever\n\n" " </a>\n" "</p>\n") matches = re.finditer(regex, test_str) 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