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- [/==============================================================================
- Copyright (C) 2001-2011 Joel de Guzman
- Copyright (C) 2001-2011 Hartmut Kaiser
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
- ===============================================================================/]
- [section:lexer Supported Regular Expressions]
- [table Regular expressions support
- [[Expression] [Meaning]]
- [[`x`] [Match any character `x`]]
- [[`.`] [Match any except newline (or optionally *any* character)]]
- [[`"..."`] [All characters taken as literals between double quotes, except escape sequences]]
- [[`[xyz]`] [A character class; in this case matches `x`, `y` or `z`]]
- [[`[abj-oZ]`] [A character class with a range in it; matches `a`, `b` any
- letter from `j` through `o` or a `Z`]]
- [[`[^A-Z]`] [A negated character class i.e. any character but those in
- the class. In this case, any character except an uppercase
- letter]]
- [[`r*`] [Zero or more r's (greedy), where r is any regular expression]]
- [[`r*?`] [Zero or more r's (abstemious), where r is any regular expression]]
- [[`r+`] [One or more r's (greedy)]]
- [[`r+?`] [One or more r's (abstemious)]]
- [[`r?`] [Zero or one r's (greedy), i.e. optional]]
- [[`r??`] [Zero or one r's (abstemious), i.e. optional]]
- [[`r{2,5}`] [Anywhere between two and five r's (greedy)]]
- [[`r{2,5}?`] [Anywhere between two and five r's (abstemious)]]
- [[`r{2,}`] [Two or more r's (greedy)]]
- [[`r{2,}?`] [Two or more r's (abstemious)]]
- [[`r{4}`] [Exactly four r's]]
- [[`{NAME}`] [The macro `NAME` (see below)]]
- [[`"[xyz]\"foo"`] [The literal string `[xyz]\"foo`]]
- [[`\X`] [If X is `a`, `b`, `e`, `n`, `r`, `f`, `t`, `v` then the
- ANSI-C interpretation of `\x`. Otherwise a literal `X`
- (used to escape operators such as `*`)]]
- [[`\0`] [A NUL character (ASCII code 0)]]
- [[`\123`] [The character with octal value 123]]
- [[`\x2a`] [The character with hexadecimal value 2a]]
- [[`\cX`] [A named control character `X`.]]
- [[`\a`] [A shortcut for Alert (bell).]]
- [[`\b`] [A shortcut for Backspace]]
- [[`\e`] [A shortcut for ESC (escape character `0x1b`)]]
- [[`\n`] [A shortcut for newline]]
- [[`\r`] [A shortcut for carriage return]]
- [[`\f`] [A shortcut for form feed `0x0c`]]
- [[`\t`] [A shortcut for horizontal tab `0x09`]]
- [[`\v`] [A shortcut for vertical tab `0x0b`]]
- [[`\d`] [A shortcut for `[0-9]`]]
- [[`\D`] [A shortcut for `[^0-9]`]]
- [[`\s`] [A shortcut for `[\x20\t\n\r\f\v]`]]
- [[`\S`] [A shortcut for `[^\x20\t\n\r\f\v]`]]
- [[`\w`] [A shortcut for `[a-zA-Z0-9_]`]]
- [[`\W`] [A shortcut for `[^a-zA-Z0-9_]`]]
- [[`(r)`] [Match an `r`; parenthesis are used to override precedence
- (see below)]]
- [[`(?r-s:pattern)`] [apply option 'r' and omit option 's' while interpreting pattern.
- Options may be zero or more of the characters 'i' or 's'.
- 'i' means case-insensitive. '-i' means case-sensitive.
- 's' alters the meaning of the '.' syntax to match any single character whatsoever.
- '-s' alters the meaning of '.' to match any character except '`\n`'.]]
- [[`rs`] [The regular expression `r` followed by the regular
- expression `s` (a sequence)]]
- [[`r|s`] [Either an `r` or and `s`]]
- [[`^r`] [An `r` but only at the beginning of a line (i.e. when just
- starting to scan, or right after a newline has been
- scanned)]]
- [[`r`$] [An `r` but only at the end of a line (i.e. just before a
- newline)]]
- ]
- [note POSIX character classes are not currently supported, due to performance issues
- when creating them in wide character mode.]
- [tip If you want to build tokens for syntaxes that recognize items like quotes
- (`"'"`, `'"'`) and backslash (`\`), here is example syntax to get you started.
- The lesson here really is to remember that both c++, as well as regular
- expressions require escaping with `\` for some constructs, which can
- cascade.
- ``
- quote1 = "'"; // match single "'"
- quote2 = "\\\""; // match single '"'
- literal_quote1 = "\\'"; // match backslash followed by single "'"
- literal_quote2 = "\\\\\\\""; // match backslash followed by single '"'
- literal_backslash = "\\\\\\\\"; // match two backslashes
- ``
- ]
- [heading Regular Expression Precedence]
- * `rs` has highest precedence
- * `r*` has next highest (`+`, `?`, `{n,m}` have the same precedence as `*`)
- * `r|s` has the lowest precedence
- [heading Macros]
- Regular expressions can be given a name and referred to in rules using the
- syntax `{NAME}` where `NAME` is the name you have given to the macro. A macro
- name can be at most 30 characters long and must start with a `_` or a letter.
- Subsequent characters can be `_`, `-`, a letter or a decimal digit.
- [endsect]
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