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
  • Match everything enclosed
    (?:...)
  • Capture everything enclosed
    (...)
  • 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

/
/

Test String

Substitution

Processing...

Code Generator

Generated Code

using System; using System.Text.RegularExpressions; public class Example { public static void Main() { string pattern = @/ (?xsm) # free-spacing mode, DOTALL, multi-line (?=.*?blue) # if blue isn't there, fail without delay ########### LINE SKIPPER / COUNTER ############ (?: # start non-capture group # the aim is to skip lines that don't contain blue # and capture a corresponding digit sequence (?: # skip one line that doesn't contain blue ^ # beginning of line (?:(?!blue)[^\r\n])* # zero or more chars # that do not start blue (?:\r?\n) # newline chars ) # With each line skipped, let Group 1 capture # an ever-growing portion of the string of numbers (?= # lookahead .* # Go to the end of the file ( # start Group 1 ~\d+ # match a tilde and digits (?(1)\1) # if Group 1 is set, match Group 1 ) # end Group 1 ) # end lookahead )*+ # end counter-line-skipper: zero or more times # the possessive + forbids backtracking .*? # lazily match any chars up to... blue # match blue .* # Get to the end of the data ~ # match a tilde \K # drop what we matched so far \d+ # match digits. This is the match! (?=(?(1)\1)) # if Group 1 has been set, match it /; string substitution = @""; string input = @"Paint it white Paint it black Why not blue? Or red or brown? ~10~9~8~7~6~5~4~3~2~1"; Regex regex = new Regex(pattern); string result = regex.Replace(input, substitution, 1); } }

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