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. Here is a simple explanation on how this works. The above regular expression will first try to m...

When we need to process a HTML page source code, we often need to retrieve the meta description of the page besides the links in the page. This description is usually located in <meta> tag of a HTML page. The meta description is very useful for search engine index. How can we retrieve the meta description? If we use a regular expression, we can easily get the meta description.In JavaScript, the regular expression looks like :var pattern = /<meta.*?name="description".*?content="(.*?)".*?>|<meta.*?content="(.*?)".*?name="description".*?>/i;since the description is the content i...

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.CharacterMeaningcGeneral 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] == '^')        return matchhere(regexp+1,text);     do{ /*Check the strin...

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=/(.+:\/\/)?([^\/]+)(\/.*)*/i;the regular expression pattern can be used to get the hostname. There are three...