# C# Regular Expressions

This page contains 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. Matchesat least n and at most m times. For example, “o{1,3}” matchesthe 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. |