Thank you for thereply.
with case changes that worked But:
when I am trying to get the data in Json.which I think is better to parser:
http://en.wikipedia.org/w/api.php?format=json&action=query&titles=United_States&prop=revisions&rvprop=content 

I see that I am getting lot of data like:
==
 \u0906\u0923\u093f \u092a\u094d\u0930\u0926\u0947\u0936]]\n[[ms:Negeri dan wilayah di India]]\n[[nl:Lijst van staten en territoria van India]]\n[[ne:\u092d\u093e\u0930\u0924\u0915\u093e \u0930\u093e\u091c\u094d\u092f\u0939\u0930\u0941 \u0930 \u0915\u0947\u0928\u094d\u0926\u094d\u0930 \u0936\u093e\u0938\u093f\u0924 \u0930\u093e\u091c\u094d\u092f\u0939\u0930\u0941]]\n[[ja:\u30a4\u30f3\u30c9\u306e\u5730\u65b9\u884c\u653f\u533a\u753b]]\n[[no:Indias delstater og territorier]]\n[[nn:Statar og territorium i India]]\n[[or:\u0b2d\u0b3e\u0b30\u0b24\u0b30
is my query correct? all I need is to get the 
Leading population centers




From: Platonides <platonides@gmail.com>
To: Pavan Kumar <pavankumarstudent@yahoo.com>; MediaWiki API announcements & discussion <mediawiki-api@lists.wikimedia.org>
Sent: Thursday, August 9, 2012 4:14 AM
Subject: Re: [Mediawiki-api] getting data for a topic

On Thu, Aug 9, 2012 at 8:16 AM, Pavan Kumar <pavankumarstudent@yahoo.com> wrote:
Hi all,
I am new to wikipedia API.
can you help me with the following:
I want to grep all the content of the "united states of america" to a text file with out images.
I am looking a response in text format.

How can I do that?
looking for: http://en.wikipedia.org/wiki/United_States  page contents.

I got this url constructed:
http://en.wikipedia.org/w/api.php?format=xml&action=query&titles=united_states&prop=revisions&rvprop=content 
But I am not getting what I want ..:(.may be I am missing some thing basic

A simple mistake: You are writing the article in lowercase.
 

Try with http://en.wikipedia.org/w/api.php?format=xml&action=query&titles=United_States&prop=revisions&rvprop=content


1.how can I get the content of what ever string I give in the query?
    please help me with the url.
2. I am trying to have this in a text file. can I get the response in the text format? other than xml and json?
3. In the unites_states example, I want to get the  first coulm of the citys (
Leading population centers

)
how can I get that .   

Extracting content from the inside of the article content will require you to perform some parsing of the wikitext.