create a login form shortcode

// functions.php

// wp login form shortcode
function devpress_login_form_shortcode() {
	if ( is_user_logged_in() )
		return '';

	return wp_login_form( array( 'echo' => false ) );
}

function devpress_add_shortcodes() {
	add_shortcode( 'devpress-login-form', 'devpress_login_form_shortcode' );
}

add_action( 'init', 'devpress_add_shortcodes' );


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// shortcode usages

<?php echo do_shortcode('[devpress-login-form]');?>



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// only can use this                           <?php wp_login_form(); ?>

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source link:http://www.wprecipes.com/how-to-create-a-login-form-shortcode-for-your-wordpress-blog