C# Regular Expressions Cheat Sheet

C#

Cheat sheet for C# regular expressions metacharacters, operators, quantifiers etc

Character
Description
\

Marks the next character as either a special character or escapes a literal. For example, "n" matches the character "n". "\n" matches a newline character. The sequence "\\" matches "\" and "\(" matches "(".

Note: double quotes may be escaped by doubling them: "<a href=""...>"

^ Depending on whether the MultiLine option is set, matches the position before the first character in a line, or the first character in the string.
$ Depending on whether the MultiLine option is set, matches the position after the last character in a line, or the last character in the string.
* Matches the preceding character zero or more times. For example, "zo*" matches either "z" or "zoo".
+ Matches the preceding character one or more times. For example, "zo+" matches "zoo" but not "z".
? Matches the preceding character zero or one time. For example, "a?ve?" matches the "ve" in "never".
. Matches any single character except a newline character.
(pattern) Matches pattern and remembers the match. The matched substring can be retrieved from the resulting Matches collection, using Item [0]...[n]. To match parentheses characters ( ), use "\(" or "\)".
(?<name>pattern) Matches pattern and gives the match a name.
(?:pattern) A non-capturing group
(?=...) A positive lookahead
(?!...) A negative lookahead
(?<=...) A positive lookbehind .
(?<!...) A negative lookbehind .
x|y Matches either x or y. For example, "z|wood" matches "z" or "wood". "(z|w)oo" matches "zoo" or "wood".
{n} n is a non-negative integer. Matches exactly n times. For example, "o{2}" does not match the "o" in "Bob," but matches the first two o's in "foooood".
{n,} n is a non-negative integer. Matches at least n times. For example, "o{2,}" does not match the "o" in "Bob" and matches all the o's in "foooood." "o{1,}" is equivalent to "o+". "o{0,}" is equivalent to "o*".
{n,m} m and n are non-negative integers. Matches at least n and at most m times. For example, "o{1,3}" matches the first three o's in "fooooood." "o{0,1}" is equivalent to "o?".
[xyz] A character set. Matches any one of the enclosed characters. For example, "[abc]" matches the "a" in "plain".
[^xyz] A negative character set. Matches any character not enclosed. For example, "[^abc]" matches the "p" in "plain".
[a-z] A range of characters. Matches any character in the specified range. For example, "[a-z]" matches any lowercase alphabetic character in the range "a" through "z".
[^m-z] A negative range characters. Matches any character not in the specified range. For example, "[m-z]" matches any character not in the range "m" through "z".
\b Matches a word boundary, that is, the position between a word and a space. For example, "er\b" matches the "er" in "never" but not the "er" in "verb".
\B Matches a non-word boundary. "ea*r\B" matches the "ear" in "never early".
\d Matches a digit character. Equivalent to [0-9].
\D Matches a non-digit character. Equivalent to [^0-9].
\f Matches a form-feed character.
\k A back-reference to a named group.
\n Matches a newline character.
\r Matches a carriage return character.
\s Matches any white space including space, tab, form-feed, etc. Equivalent to "[ \f\n\r\t\v]".
\S Matches any nonwhite space character. Equivalent to "[^ \f\n\r\t\v]".
\t Matches a tab character.
\v Matches a vertical tab character.
\w Matches any word character including underscore. Equivalent to "[A-Za-z0-9_]".
\W Matches any non-word character. Equivalent to "[^A-Za-z0-9_]".
\num Matches num, where num is a positive integer. A reference back to remembered matches. For example, "(.)\1" matches two consecutive identical characters.
\n Matches n, where n is an octal escape value. Octal escape values must be 1, 2, or 3 digits long. For example, "\11" and "\011" both match a tab character. "\0011" is the equivalent of "\001" & "1". Octal escape values must not exceed 256. If they do, only the first two digits comprise the expression. Allows ASCII codes to be used in regular expressions.
\xn Matches n, where n is a hexadecimal escape value. Hexadecimal escape values must be exactly two digits long. For example, "\x41" matches "A". "\x041" is equivalent to "\x04" & "1". Allows ASCII codes to be used in regular expressions.
\un Matches a Unicode character expressed in hexadecimal notation with exactly four numeric digits. "\u0200" matches a space character.
\A Matches the position before the first character in a string. Not affected by the MultiLine setting
\Z Matches the position after the last character of a string. Not affected by the MultiLine setting.
\G Specifies that the matches must be consecutive, without any intervening non-matching characters.

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34 Comments

- Steve

Thanks. Been quite a while since I last used Regular Expressions. Your cheat sheet is just what the doctor ordered.

- Dhwanit

Thanks! This was very helpful!

- pat

Maybe also good to mention that "?" can be used to indicate non-greedy match ie .*? Often quite handy

- DJ

Anyone know the correct way to check for the dash/minus "-" character?

- Mike

DJ:

Escape it with a backslash: \-

- Jeff

The descriptions for \W and \w are not completely correct.

You say they're equivalent to [A-Za-z0-9] or [^A-Za-z0-9] when in fact \w allows extended ASCII chars to pass through, e.g. accented letters from non-English languages.

- Rick

Thanks for the great resource. I was wondering if I could link to your article from a help file I'm creating for my company's product which uses c# regular expressions to search through a text file.

- Mike

@Rick

Yes, by all means

- Roland

Cool, but now how do I use it in code?

- Alister

One that's missing:

\k : a back-reference to a named group.

- Mike

@Roland

Huh?

- Tim

I tried using (pattern) to parse out "(Preferred)" from a string and Visual C# 2008 required me to enter it as (\\(Preferred\\)) . So in order to match parentheses characters ( ), it should be listed as "\\(" or "\\)" not "\(" or "\)" as stated above.

- Tomas

How can I write expression with negative number?.. like Column = -8. It doesn't work and result is empty ..

- Steve Wellens

Very nice.

I hope you don't mind me pointing out a very useful, and more importantly free, tool for developing Regular Expressions.

http://www.ultrapico.com/Expresso.htm

- Mike

@Steve,

Thanks for that. I've kept meaning to update this entry with a link to Expresso. You've done it for me now :o)

- Marc D

Dude... awesome cheat sheet. I just started learning/using/attempting to use reg expressions, so this list rocks:D One thing I think would be great would be how to put together patterns. Some of the patterns out there are just confusing looking. Anyway.. Good job!

- greensweater

One that's missing: \k : a back-reference to a named group.

as in:

^(?[0-9]*)=\k$

123=123 match
123=456 fail

- Mike

@Alister and greensweater

I've added \k now. Thanks for pointing it out.

- Jonas

Regular expression comment(#) is missing.

- chhanda

Excellent

- vijay

Thanks for your help.

- alexitosrv

Nice resource. Also Expresso is such a great tool.

Thank you very much.

- Alistair

\x for stripping non printable ascii characters is a life saver for me. The samples on Regexlib.com just don't work in .NET. Thanks for providing this resource. No wonder it's the most popular page on your great site!

- mark

whats the modifier to make searches/matches case insensitive?

thanks

- Mike

@mark

For .NET, you apply it as a RegexOptions parameter: http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regexoptions.aspx

- suddu

As Tim said,for parenthesis you should use \\( and \\)

- Niels Heurlin

Ok as a cheat sheet. I was hoping for some examples.

- Dominic

Thanks, this saved my day!

I needed an expression to match anything (including newlines and embedded HTML tags) in the element of an HTML document.

This worked in C#:
pattern = @"";

- dev

please send me regularexpression for
(mm/dd/yyyy HH:MM:SS AM/PM)

Thank you

- Mike

@dev,

You don't need a regular expression. You need DateTime.TryParse().

- Art

Haha, I can't believe you bothered responding to "dev"...

Anyway, thanks for the great resource!

- Ric

The \un example should be "\u0020", rather than "\u0200"--that would give you Ȁ instead.

- Satyabrata Mohapatra

All in one place.

Thanks.

- zircon747

thanks
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