SLRE: Super Light Regular Expression library ============================================ SLRE is an ISO C library that implements a subset of Perl regular expression syntax. Main features of SLRE are: * Written in strict ANSI C'89 * Small size (compiled x86 code is about 5kB) * Uses little stack and does no dynamic memory allocation * Provides simple intuitive API * Implements most useful subset of Perl regex syntax (see below) * Easily extensible. E.g. if one wants to introduce a new metacharacter `\i`, meaning "IPv4 address", it is easy to do so with SLRE. SLRE is perfect for tasks like parsing network requests, configuration files, user input, etc, when libraries like [PCRE](http://pcre.org) are too heavyweight for the given task. Developers of embedded systems would benefit most. ## Supported Syntax (?i) Must be at the beginning of the regex. Makes match case-insensitive ^ Match beginning of a buffer $ Match end of a buffer () Grouping and substring capturing \s Match whitespace \S Match non-whitespace \d Match decimal digit + Match one or more times (greedy) +? Match one or more times (non-greedy) * Match zero or more times (greedy) *? Match zero or more times (non-greedy) ? Match zero or once (non-greedy) x|y Match x or y (alternation operator) \meta Match one of the meta character: ^$().[]*+?|\ \xHH Match byte with hex value 0xHH, e.g. \x4a [...] Match any character from set. Ranges like [a-z] are supported [^...] Match any character but ones from set Under development: Unicode support. ## API int slre_match(const char *regexp, const char *buf, int buf_len, struct slre_cap *caps, int num_caps); `slre_match()` matches string buffer `buf` of length `buf_len` against regular expression `regexp`, which should conform the syntax outlined above. If regular expression `regexp` contains brackets, `slre_match()` can capture the respective substrings into the array of `struct slre_cap` structures: /* Stores matched fragment for the expression inside brackets */ struct slre_cap { const char *ptr; /* Points to the matched fragment */ int len; /* Length of the matched fragment */ }; N-th member of the `caps` array will contain fragment that corresponds to the N-th opening bracket in the `regex`, N is zero-based. `slre_match()` returns number of bytes scanned from the beginning of the string. If return value is greater or equal to 0, there is a match. If return value is less then 0, there is no match. Negative return codes are as follows: #define SLRE_NO_MATCH -1 #define SLRE_UNEXPECTED_QUANTIFIER -2 #define SLRE_UNBALANCED_BRACKETS -3 #define SLRE_INTERNAL_ERROR -4 #define SLRE_INVALID_CHARACTER_SET -5 #define SLRE_INVALID_METACHARACTER -6 #define SLRE_CAPS_ARRAY_TOO_SMALL -7 #define SLRE_TOO_MANY_BRANCHES -8 #define SLRE_TOO_MANY_BRACKETS -9 ## Example: parsing HTTP request line const char *request = " GET /index.html HTTP/1.0\r\n\r\n"; struct slre_cap caps[4]; if (slre_match("^\\s*(\\S+)\\s+(\\S+)\\s+HTTP/(\\d)\\.(\\d)", request, strlen(request), caps, 4) > 0) { printf("Method: [%.*s], URI: [%.*s]\n", caps[0].len, caps[0].ptr, caps[1].len, caps[1].ptr); } else { printf("Error parsing [%s]\n", request); } ## Example: find all URLs in a string static const char *str = " " " some link"; static const char *regex = "(?i)((https?://)[^\\s/'\"<>]+/?[^\\s'\"<>]*)"; struct slre_cap caps[2]; int i, j = 0, str_len = strlen(str); while (j < str_len && (i = slre_match(regex, str + j, str_len - j, caps, 2, NULL)) > 0) { printf("Found URL: [%.*s]\n", caps[0].len, caps[0].ptr); j += i; } Output: Found URL: [HTTPS://FOO.COM/x?b#c=tab1] Found URL: [http://cesanta.com] # Licensing SLRE is dual licensed. It is available either under the terms of [GNU GPL v.2 license](http://www.gnu.org/licenses/old-licenses/gpl-2.0.html) for free, or under the terms of standard commercial license provided by [Cesanta Software](http://cesanta.com). Businesses who whish to use Cesanta's products must [license commercial version](http://cesanta.com/products.html). [Super Light DNS Resolver](https://github.com/cesanta/sldr), [Mongoose web server](https://github.com/cesanta/mongoose) are other projects by Cesanta Software, developed with the same philosophy of functionality and simplicity.