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Regular Expressions Quick Reference

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Modified on Mon, Feb 13, 2012, 12:52 PM by Administrator Categorized as (Favorites), Quick Reference, Regular Expressions

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Special Characters¶

Character	Usage
`[`	starts a character class
`\`	cancels the special meaning of the next character
`^` (caret)	start-of-string anchor
`$`	end-of-string anchor
`.`	Matches any character except for line breaks
`\|` (pipe)	alternation group
`?`	indicates the previous character or group is optional. Equivalent to `{0,1}`
`*` (asterisk)	-
`+`	-
`(`	-
`)`	-

Text	Description
`\f`	Form feed (ASCII 12)
`\n`	Line feed (ASCII 10)
`\r`	Carriage return (ASCII 13)
`\t`	Tab (ASCII 9)
`\v`	Vertical tab (ASCII 11)
`\a`	Alarm (ASCII 7)
`\e`	Escape (ASCII 25)
`\xxx`	The ASCII character specified by the octal number `xxx`
`\xnn`	The ASCII character specified by the hexadecimal number `nn`
`\cX`	The control character `Control-X`. For example, `\cI` is equivalent to `\t` and `\cJ` is equivalent to `\n`.

A character class matches one out of a set of characters.

Text	Description
`[...]`	Any one character between the brackets.
`[^...]`	Any one character not between the brackets.
`.`	Any character except newline. Equivalent to `[^\n]`
`\w`	Any word character. Equivalent to `[a-zA-Z0-9_]` and `[[:alnum:]_]`
`\W`	Any non-word character. Equivalent to `[^a-zA-Z0-9_]` and `[^[:alnum:]_]`
`\s`	Any whitespace character. Equivalent to `[ \t\n\r\f\v]` and `[[:space:]]`
`\S`	Any non-whitespace. Equivalent to `[^ \t\n\r\f\v]` and `[^[:space:]]` Note: `\w != \S`
`\d`	Any digit. Equivalent to `[0-9]` and `[[:digit:]]`
`\D`	Any character other than a digit. Equivalent to `[^0-9]` and `[^[:digit:]]`
`[\b]`	A literal backspace (special case)
`[[:class:]]`	`class` can be one of the following: `alnum, alpha, ascii, blank, cntrl, digit, graph, lower, print, punct, space upper, xdigit`

Text	Description
`\`	Turn off the special meaning of the following character.
`\n`	Restore the text matched by the nth pattern previously saved by `$` and `$`. n is a number from 1 to 9, with 1 starting on the left.
`&`	Reuse the text matched by the search pattern as part of the replacement pattern.
`~`	Reuse the previous replacement pattern in the current replacement pattern. Must be the only character in the replacement pattern. (ex and vi).
`%`	Reuse the previous replacement pattern in the current replacement pattern. Must be the only character in the replacement pattern. (ed).

Text	Description
`^` (caret)	matches start of string
`$`	matches end of string
`\b`	matches word boundary (a position between a character that can be matched by `\w` and one that cannot
`\B`	negation of `\b`
`\u`	Convert first character of replacement pattern to uppercase.
`\U`	Convert entire replacement pattern to uppercase.
`\l`	Convert first character of replacement pattern to lowercase.
`\L`	Convert entire replacement pattern to lowercase.

Pattern	Description
`{n,m}`	Match the previous item at least `n` times but no more than `m` times.
`{n,}`	Match the previous item `n` or more times.
`{n}`	Match exactly `n` occurrences of the previous item.
`?`	Match zero or one occurrences of the previous item. Equivalent to `{0,1}`
`+`	Match one or more occurrences of the previous item. Equivalent to `{1,}`
`*`	Match zero or more occurrences of the previous item. Equivalent to `{0,}`
`{}?`	Non-greedy match - will not include the next match's characters.
`??`	Non-greedy match.
`+?`	Non-greedy match.
`*?`	Non-greedy match. For example, in `^(.?)\s$` the grouped expression will not include trailing spaces.

Text	Description
`g`	Perform a global match. That is, find all matches rather than stopping after the first match.
`i`	Do case-insensitive pattern matching.
`m`	Treat string as multiple lines (`^` and `$` match internal `\n`).
`s`	Treat string as single line (`^` and `$` ignore `\n`, but `.` matches `\n`).
`x`	Extend your pattern's legibility with whitespace and comments.

Pattern	Description
`(?#abc)`	Comment; `abc` is ignored.
`(?:abc)`	Matches but doesn't return `abc`
`(?=abc)`	Matches if expression would match `abc` next. This is called a non-consuming search, and can be used to match several search terms independent of what order they appear.
`(?!abc)`	Matches if expression wouldn't match `abc` next
`(?imsx)`	Change matching rules (see options) midway through an expression.

Pattern	Description
`(...)`	Grouping. Group several items into a single unit that can be used with `*`, `+`, `?`, `\|`, and so on, and remember the characters that match this group for use with later references.
`(?<name>...)`	Named group
`\|`	Alternation. Match either the subexpressions to the left or the subexpression to the right.
`\n`	Match the same characters that were matched when group number n was first matched. Groups are subexpressions within (possibly nested) parentheses.
`^` (caret)	Match the beginning of the string, and, in multiline searches, the beginning of a line.
`$`	Match the end of the string, and, in multiline searches, the end of a line.
`\b`	Match a word boundary. That is, match the position between a `\w` character and a `\W` character. (Note, however, that `[\b]` matches backspace.)
`\B`	Match a position that is not a word boundary.