common regex cookbook

I see nice regexes on the java forums from time to time, i am going to add them all here for use!

<br />//1. replace leading white space in a line:<br />str = str.replaceAll("(?m)(?<=^ *) ", ".");<br /><br />

regex to split a document into words

Say you wanted to split a document into words, but works like are'nt shouldnt be split on the ' and numbers like 10,004,333 should remain intact, but other punctuation should be removed from the resulting word array.

A good way to do this is using Scanner's findWithinHorizon and a regular expression. This way you dont need to read the entire document into memory before processing it.

<br />Pattern p = Pattern.compile("[A-Za-z]+(?:['-][A-Za-z]+)?|\\d+(?:[,.]\\d+)?");<br />Scanner sc = new Scanner(new File("/path/to/the/file.txt"));<br />String word = null;<br />while ((word = sc.findWithinHorizon(p, 0)) != null)<br />{<br /> // etc.<br />}<br />

extract links from a webpage

this is useful if you decide to make a web crawler, and dont want to bother with an html parser. You have to read the body of the page into a string, and then use this regex to extract all the links.

supported link types: <img src=...<a href=...
<br /><br />String body = "..."; //body of the page<br />Matcher m = Pattern.compile("(?im)(?:(?:(?:href)|(?:src))[ ]*?=[ ]*?[\"'])(((?:http|https)(?::\\/{2}[\\w]+)(?:[\\/|\\.]?)(?:[^\\s\"]*))|((?:\\/{0,1}[\\w\\.]+)+))[\"']").matcher(body);<br />while(m.find()){<br />String absolute = m.group(2);<br />String relative = m.group(3);<br />}<br />

an absolute url is in the form of "http://something.com/blah"
a relative url is in the form of "/something/path.blee"

now you can figure out what to do with these...

Remove HTML tags regex

when using an HTML parser is too much work, you may want to use a small regex to remove all the html tags

this is java:
<br />String output = input.replaceAll("</?\\w++[^>]*+>", "");<br />

Javascript: matching with regex

There seem to be 3 ways to use regular expressions in javascript:
1.
var val = document.getElementById("some_id").value;
val.replace(/^\s+|\s+$/g, ""); //trim using regex
2.
var alpha = /^[A-Za-z]+$/ ;
var val = document.getElementById("some_id").value;
if(alpha.test(val)){
//val matches alpha
}
3.

var val = document.getElementById("some_id").value;
var alpha ='((?:[a-z][a-z]+))'; // Word 1
var p = new RegExp(alpha,["i"]);
var m = p.exec(val);
if (m.length>0)
{
   var word=m[1];
   //word is the capture group 1
}

if anyone knows a better way, feel free to share.