WoW Lua string.find(s, pattern [, init [, plain]]) strfind(s, pattern [, init [, plain]]) Find the first occurrence of the pattern in the string passed. Once complex patterns are involved, sticking to string.find() is clearly no longer desirable. To go with “j”, is the “o” which enables compile-once mode. If you’re familiar with Perl, PHP, and a host of other languages, the capabilities and syntax will be familiar. The OpenRESTY project currently is recommending using Luajit 2.1, presumably for performance reasons, but I’ve yet to find good benchmark data comparing the two. There’s a, potentially larger, second problem here though. giving lower case characters a higher priority than all of the upper case characters? The following solutions show how to implement support for interpolating variables into strings in Lua to achieve a syntax somewhat like this: Here's one simple implementation (-- RiciLake): Here's another implementation (-- RiciLake) supporting Pythonic formatting specifications (requires Lua 5.1 or greater): Here's another Lua-only solution (-- MarkEdgar): Both Ruby and Python have a short form for string formatting, using the % operator. Representing a string as a table of string fragments (sometimes called a 'rope') is much more efficient. On the Nginx-Lua side of things there’s ngx.re.find() (lua-nginx-module docs) which allows calls into Nginx’s regex engine. -- Pythonic "%" operator for srting interpolation. I’ve done a significant amount of digging trying to find performance informational about both of these methods, and I haven’t been able to find any. The table shows the 4 test processes that I arranged (not all are going to be useful in each test scenario) with the results for an individual operation in microseconds (10^-6 seconds) for each fo the 5 tested input sizes (approximately 2^4, 2^6, 2^8, 2^10, and 2^12 characters). The idea is simple: By giving a device (real or dummy) in Domoticz a name constructed by adding a pre-determined prefix to an existing device/group name, Lua is used to detect when *any* device with that prefix changes state and to carry out a specific action on an existing physical device/group defined already in Domoticz (and named with… -- obtain local variable from (1 if omitted). Every 5 characters a space is inserted. This makes use of the debug library (particularly debug.getlocal()) to query locals, which might be undesirable for a number of reasons (-- RiciLake). The early takeaway is to always use string.find() when you can exactly match the string you’re searching for. Or well the other option is to convert the string to all upper or lower case. That is if the target string is the first entry in the table, the looped Lua find function performs identically to the a single string.find() call. What the patch does is quite literally convert the above to: The following functions are updated in the llex.c file. When I published my last article looking at lua-nginx performance in a WAF like role in front of WordPress, I noted that when lua was enabled I was seeing a 425 µs increase in latency of no processing at al (including no PHP based WordPress security plugins[1]). Compare(String, String, Boolean) Compares two specified String objects, ignoring or honoring their case, and returns an integer that indicates their relative position in the sort order.. Things like, know bad user agents, key bits used in SQL injection attacks, and various things like that. -- It only accepts a single string argument. One of the behaviors of the Lua find loop that I previously described is that it’s sensitive to the position of the matching text in the input table. So while exact searches are best done with Lua’s string find regardless of the size of the search space. This is obviously adds an O(n) scaling factor to the situation as far as processing goes. Lossless compression for any text. The complaint concerning the Lua version is that the quoting is verbose and can make it more difficult to read, such as in visually distinguishing what text is inside or outside of the quotes. For the Lua find, the following pattern was fed into the loop find function that I described earlier. “J” enables the PCRE JIT compilation engine. If you are a C programmer, this may seem massively inefficient, but the answer is that Lua strings are not the right data structure for modification. To convert a string to lower case, use string.lower(str). [[Hello |name|, welcome to |get_company_name()|. What I’m most interested in here is the behavior of the regex implementation relative to the previous test when there were only a few alternative matches to be considered. std::string s("123"); int i; std::from_chars(s.data(), s.data() + s.size(), i, 10); To put it bluntly, performance testing string matching functions is a challenge. Compare(String, String, StringComparison) -- Retrieves table of all local variables (name, value), -- in given function . There are a couple of points to take away from this test. Most programming languages that have a string datatype will have some string functions although there may be other low-level ways within each language to handle strings directly. While much of the search capabilities looks somewhat like regex in spirit and format, there are significant deficiencies in the string.find() engine that separate it from regex. It takes one optional string parameter representing a Lua user type that the method would use to cast the return object into. In that article, I saw approximately 425 microsecond latency impact form the Lua processing compared to just building the page. With a WordPress security plugin, like Wordfence security, I was seeing an added 10-20 ms (milliseconds) of latency from the security process (that is compared to not having Wordfence running at all). It’s at this point that we start to see the problem. On the Lua side, there’s the built in string.find() (Lua5.1 docs) and associated functions. It uses the "|" character to represent the open and close braces. This test looks at matching against multiple terms in a string. … Because Lua doesn’t offer an efficient way to process multiple alternatives in a single expression, one has to fall back to a nested loop situation. However, specifically in Lua, there is a generic Get() method which takes advantage of Lua being type less, so the method can unbox a Variant object and return the stored object as a type less Lua object. Of course, that was still on the order of 2 orders of magnitude faster than doing the same work in PHP. Here's a simple example: Here, we call the function named print with only one argument - the constant expression "Hello". The Corona string library provides generic functions for string manipulation, such as pattern matching and finding/extracting substrings. I don't know if there is the solution to this problem as yet. Compare to Perl, where variables can be embedded in strings: The complaint concerning the Lua version is that the quoting is verbose and can make it more difficult to read, such as in visually distinguishing what text is inside or outside of the quotes. S string find 7 alternatives to look for to 52, a 7.4x increase in patterns quite literally convert string! Matching functions is a more complex implementation ( -- DavidManura ), -- given. Retrieves table of unique strings magnitude faster than doing the same as the previous example for example, to double. 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