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 = "^(?!.*?_.*?)(?!(?:[\\d\\w]+?\\.)?\\-[\\w\\d\\.\\-]*?)(?![\\w\\d]+?\\-\\.(?:[\\d\\w\\.\\-]+?))(?=[\\w\\d])(?=[\\w\\d\\.\\-]*?\\.+[\\w\\d\\.\\-]*?)(?![\\w\\d\\.\\-]{254})(?!(?:\\.?[\\w\\d\\-\\.]*?[\\w\\d\\-]{64,}\\.)+?)[\\w\\d\\.\\-]+?(?<![\\w\\d\\-\\.]*?\\.[\\d]+?)(?<=[\\w\\d\\-]{2,})(?<![\\w\\d\\-]{25})$"; final String string = "# TEST\n\n" + "## List of valid domains:\n" + "www.google.com\n" + "google.com\n" + "mkyong123.com\n" + "mkyong-info.com\n" + "sub.mkyong.com\n" + "sub.mkyong-info.com\n" + "mkyong.com.au\n" + "g.co\n" + "a.12E\n" + "mkyong.t.t.co\n" + "xn--stackoverflow.com\n" + "stackoverflow.xn--com\n" + "xn--d1ai6ai.xn--p1ai\n" + "stackoverflow.co.uk\n" + "a.xn--wgbh1c\n" + "1.2.3.4.com\n" + "x.XN--VERMGENSBERATUNG-PWB\n" + "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.com\n" + "www.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.com\n" + "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.com\n\n" + "## List of invalid domains:\n" + "http://google.com\n" + "http://www.google.com\n" + "dot.\n" + "space com\n" + "under_score.com\n" + "underscore.c_om\n" + "-dash.com\n" + "dash-.com\n" + "sub.-dash.com\n" + "sub-.dash.com\n" + "-.com\n" + "-com\n" + ".com\n" + "com\n" + "mx.gmail.com.\n" + "mkyong.t.t.c\n" + "mkyong,com\n" + "mkyong.com/users\n" + "a.123\n" + "x.XN--VERMGENSBERATUNG-PWBB\n" + "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijkk.com\n" + "www.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijkk.co.uk\n" + "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcde.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.comm\n" + "0123456789 +-.,!@#$%^&*();\\\\/|<>\\\"\\'\n" + "12345 -98.7 3.141 .6180 9,000 +42\n\n\n" + "HELP\n\n" + "https://github.com/c-hive/guides/blob/57cbbf72f1152214a160f9be8a57e2c4dc868cfd/etc/regex.md#domains\n" + "# allowed chars\n" + "[\\w\\d\\.\\-]\n\n\n" + "EXPLAIN\n\n" + "# once upon a time...\n" + "^\n" + "# doesn't contain underscore (this is so that we can use \\w alter on)\n" + "(?![\\w\\d\\.\\-]*?_[\\w\\d\\.\\-]*?)\n" + "# doesn't contain dash at the beginning of a label\n" + "(?!(?:[\\d\\w]+?\\.)?\\-[\\w\\d\\.\\-]*?)\n" + "# doesn't contain dash at the end of a label\n" + "(?![\\w\\d]+?\\-\\.(?:[\\d\\w\\.\\-]+?))\n" + "# starts with a non-limit char\n" + "(?=[\\w\\d\\])\n" + "# contains at least 1 dot\n" + "(?=[\\w\\d\\.\\-]*?\\.+[\\w\\d\\.\\-]*?)\n" + "# not longer than 253 chars\n" + "(?![\\w\\d\\.\\-]{253})\n" + "# doesn't contain a label longer than 63 char\n" + "(?!(?:\\.?[\\w\\d\\-\\.]*?[\\w\\d\\-]{64,}\\.)+?)\n" + "# allowed chars\n" + "[\\w\\d\\.\\-]+?\n" + "# TLD is not digit-only\n" + "(?<![\\w\\d\\-\\.]*?\\.[\\d]+?)\n" + "# TLD is at least 2 characters\n" + "(?<=[\\w\\d\\-]{2,})\n" + "# TLD is at most 24 characters\n" + "(?<![\\w\\d\\-]{25})\n" + "# the end\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