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

/
/
g

Test String

Code Generator

Language

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "<p>(\\s*)(<a(.*)>)?(\\s*)(https?:\\/\\/)?(w{3}\\.)?(youtube\\.com|youtu\\.be)\\/(watch\\?v=|embed\\/)?([A-Za-z0-9-_]{11})(\\S*)(\\s*)(<\\/a>)?(\\s*)<\\/p>"; final String string = "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"; final Pattern pattern = Pattern.compile(regex); final Matcher matcher = pattern.matcher(string); while (matcher.find()) { System.out.println("Full match: " + matcher.group(0)); for (int i = 1; i <= matcher.groupCount(); i++) { System.out.println("Group " + i + ": " + matcher.group(i)); } } } }

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 Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html