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

`
`
gim

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])?|[0-9]{1,3}?/[0-9]{2})\\.)+(?:[a-z](?:[a-z0-9-]{0,61}[a-z0-9])?)?$"; final String string = "This regexp can be used to validate domain names in Golang.\n" + "While it cannot enforce the 253 character limit (with optional trailing period not included)\n" + "that can be easily done with a `len(domain) <= 253` check.\n\n" + "This can be used as-is in other languages, even with RE2 regex engine.\n" + "Non-capturing groups are used.\n" + "Example validated domains (some may be invalid per TLD rules):\n\n" + "example.com\n" + "_25._tcp.SRV.example\n" + "a.punycoded-idna.xn--zckzah\n" + "under_score.example\n" + "0/27.0.0.1.in-addr.arpa\n" + "128/32.255.255.123.in-addr.arpa\n" + "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.\n\n" + "Example invalid domains:\n\n" + "192.0.2.1\n" + "has spaces.com\n" + "easy,typo.example\n" + "23/1.invalid\n" + "domain\\.escapes.invalid\n" + "trailing_.underscore.invalid\n" + "-leading.hyphens.invalid\n" + "trailing-.hyphens.invalid\n" + "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n\n" + "TLDs have more validation, the following will not validate:\n\n" + "a\n" + "example\n" + "digit.1example\n" + "underscore._example_com\n\n" + "but with a trailing period, the same rules as non-TLD are applied:\n\n" + "a.\n" + "example.\n" + "digit.1example.\n" + "underscore._example_com.\n"; final Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE | 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