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

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]"; final String string = "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"; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE); 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