add-webapp-to-links.php

<?php
/*
Plugin Name: Add target="webapp" to links
Description: This plugin will add target="webapp" to links in the post and page content as well as in the comments.
Author: Jan Dembowski
Author URI: http://blog.dembowski.net/
*/
add_filter( 'the_content' , 'mh_webapp' , 50 );
add_filter( 'comment_text' , 'mh_webapp' , 50 );
add_action( 'wp_head' , 'mh_base' );

function mh_webapp( $content ) {
//
// Idea harvested from here http://css-tricks.com/snippets/php/find-urls-in-text-make-links/
//
$mh_url_regex = "/\<a\ href\=\"(http|https)\:\/\/[a-zA-Z0-9\-\.]+[a-zA-Z]{2,3}/";

preg_match_all( $mh_url_regex , $content, $mh_matches );

for ( $mh_count = 0; $mh_count < count( $mh_matches[0] ); $mh_count++ )
    {
    $mh_old_url = $mh_matches[0][$mh_count];
    $mh_new_url = str_replace( ' href="' , ' target="webapp" href="' , $mh_matches[0][$mh_count] );

    // Ignore any links that already have target="webapp"
    if( !preg_match( '/target\=\"webapp\"/' , $mh_old_url , $mh_dont_care ) )
        $content = str_replace( $mh_old_url , $mh_new_url , $content );
    }

return $content;
}

function mh_base() {
        echo '<base target="webapp" />';
}