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  Greedy and Nongreedy Matching in a Regular Expression

By default, pattern matching is greedy, which means that the matcher returns the longest match possible. For example, applying the pattern A.*c to AbcAbcA matches AbcAbc rather than the shorter Abc. To do nongreedy matching, a question mark must be added to the quantifier. For example, the pattern A.*?c will find the shortest match possible. COPY // Greedy quantifiers String match = find("A.*c", "AbcAbc"); // AbcAbc match = find("A.+", "AbcAbc"); // AbcAbc // Nongreedy quantifier...

   Regular expression,Pattern match,Greedy,     2011-08-09 12:42:28

  How regular expression works

Rob Pike wrote 30 lines of codes to realize a simple regular expression matcher in his book The practice of Programming. This piece of code is really cool. Let's take a look at the code.Meaning of different characters.Character Meaning c General character . Match any single character ^ Match start of a string $ Match end of a string * Match zero or many occurrences of a character /*match ：Test the regexp in text*/int match(char* regexp,char* text){    if(regexp[0] == '^')&n...

   Regular expression,Implementation,Rob Pike,C     2012-06-25 05:23:41

  A Perl Regular Expression That Matches Prime Numbers

perl -lne '(1x$_) =~ /^1?$|^(11+?)\1+$/ || print "$_ is prime"' Can you figure out how it works? I give an explanation below, but try to figure it out yourself. Here is what happens when you run it: $ perl -lne '(1x$_) =~ /^1?$|^(11+?)\1+$/ || print "$_ is prime"' 1 2 2 is prime 3 3 is prime 4 5 5 is prime 6 7 7 is prime 8 9 10 11 11 is prime Here is how it works. First, the number is converted in its unary representation by (1x$_). For example, the number 5 gets converted into 1x5, which is ...

   Perl,Regex,Regular expression,Prime number,One line     2011-12-26 08:42:00

  Fuzzy search algorithm in Sublime Text

Fuzzy string searching is the technique of finding strings that match a pattern approximately (rather than exactly. In many editors, we can easily find the Find menu item to do exact matching. While in Sublime Text and some other editors, we can use fuzzy string searching as well if we just want to have an approximate match. There is some algorithm implemented in Sublime Text to implement achieve this. First the search query is split into characters, join them with a regex wildcard, and then run...

   Sublime Text,Fuzzy search     2013-10-14 22:49:38

  The Greatest Regex Trick Ever (Simplified)

There is a post which is really hot recently which showcased a best ever regular expression trick. In this post, it provides a trick which can be adapted to situations where one wants to match some patterns desired and exclude the patterns undesired. In simple, the trick is : Pattern not desired | (Pattern desired) Then taking the group 1 match of the capturing group of matched. This group will contain the strings matching the desired patterns. Have to say this trick is really neat and brilliant...

   REGULAR EXPRESSION,PROGRAMMING,JAVA     2015-10-01 21:59:05

  Get hostname from a URL using JavaScript

Sometimes we may have strings which contain some UR;s and we may want to retrieve the hostname from the URLs for some statistic use. For example, we may have a URL : http://www.example.com/aboutus.html. We may want to retrieve the www.example.com from the URL. How? Use regular expression. Here I give an example using JavaScript. If you want to check whether a string is a URL or not. Refer to Detect URLs in a Block of Text. In JavaScript, we can have a regular expression like var pattern=/(.+:\/\...

   JavaScript,URL,regular expression, Hostname     2012-06-15 09:16:45

  An alternative way to parse URL in JavaScript

Normally when we need to process URL in JavaScript, we may use the location object. Then we can use location.hostname,location.href,location.port etc to get the information we need. In this post, we will parse an URL with an alternative way. We can use an URL to create a DOM object by calling document.createElement("a"). The complete code is: function parseURL(url) { var a = document.createElement('a'); a.href = url; return { source: url, protocol: a.protocol.replace(':',''), host: a.ho...

   URL,location,parse     2014-03-03 07:05:11

  Five-minute Multimethods in Python

So what are multimethods? I'll give you my own definition, as I've come to understand them: a function that has multiple versions, distinguished by the type of the arguments. (Some people go beyond this and also allow versions distinguished by the value of the arguments; I'm not addressing this here.) As a very simple example, let's suppose we have a function that we want to define for two ints, two floats, or two strings. Of course, we could define it as follows: def foo(a, b): if...

   Python,Multimethod,Argument list,Version,Overloadding     2011-12-07 08:41:03

  Check mobile device using JavaScript

Sometimes developers want to know whether the user is using a mobile browser or a desktop browser so that they can build corresponding user experience. Although in many cases responsive web design would help solve component alignment issues, there are performance related considerations in some cases where some code should not be ran or some feature should not be available if user is on mobile browser. or vice versa This post will summarize a few ways which are commonly used to check whether a us...

   CHECK,MOBILE BROWSER,MOBILE DEVICE,JAVASCRIPT     2021-10-02 01:36:16

  Getting started with C++ TR1 regular expressions

Overview This article is written for the benefit of someone familiar with regular expressions but not with the use of regular expressions in C++ via the TR1 (C++ Standards Committee Technical Report 1) extensions. Comparisons will be made with Perl for those familiar with Perl, though no knowledge of Perl is required. The focus is not on the syntax of regular expressions per se but rather how to use regular expressions to search for patterns and make replacements. Support for TR1 ext...

   Regular expression,Replace,TR1,Extension     2011-08-14 07:25:20

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