C# Regular Expressions Guide
Guide 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, “erb” matches the “er” in “never” but not the “er” in “verb”. |
| B | Matches a non-word boundary. “ea*rB” 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 “[ fnrtv]”. |
| S | Matches any nonwhite space character. Equivalent to “[^ fnrtv]”. |
| 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 “�11” both match a tab character. “�011” is the equivalent of “�01” & “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. |
