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

using System; using System.Text.RegularExpressions; public class Example { public static void Main() { string pattern = @"(?: |^)hostname=(?:[^\s.]+\.)*?(?P<myfield>[^\s.]+\.(?:(?:ac|co)\.uk|govt?\.uk|judiciary\.uk|l(?:ea|td)\.uk|m(?:e|il|od)\.uk|n(?:et|hs|ic)\.uk|orgn?\.uk|p(?:arliament|lc|olice)\.uk|(?:royal|sch)\.uk|[^\s.]+)(?!\S))"; string input = @"hostname=www.aaa.bbb.someurl.net hostname=www.amazon.co.uk 2021-07-20 18:19:14 reason=Not allowed to browse this category event_id=12345 protocol=HTTP action=Blocked transactionsize=16051 responsesize=789 requestsize=456 urlcategory=Blocked serverip=1.2.4.5 clienttranstime=0 requestmethod=GET refererURL=None useragent=Microsoft-Delivery location=Internal ClientIP=5.6.7.8 status=403 user=John url=dl.delivery.mp.microsoft.com/filestreamingservice/files/abcd-efgh-ijkl/pieceshash vendor=Zscaler hostname=dl.delivery.mp.microsoft.com"; RegexOptions options = RegexOptions.Multiline; foreach (Match m in Regex.Matches(input, pattern, options)) { Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index); } } }

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 C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx