Adding custom code into header.php using a plugin

Question

I have a bunch of code that I tend to put into the header.php of every site I do which are specific to Internet Explorer.

I was wondering if there was a way to insert code into a 'standard' header.php.

Yes, I can simply modify the header. But the idea is to make this a plugin which is generic.

Specifically, I'd like to create a plugin to echo the following in the header immediately after the default stylesheet:

<!--[if IE]>
  <link rel="stylesheet" href="<?php bloginfo('stylesheet_directory'); ?>/ie.css" type="text/css" />
<![endif]-->

Answer 1

One way to do it is using the wp_head action:

function wpse85495_header() {
?>
<!--[if IE]>
  <link rel="stylesheet" href="<?php bloginfo('stylesheet_directory'); ?>/ie.css" type="text/css" />
<![endif]-->
<?php
}
add_action('wp_head','wpse85495_header');

but I think the prefered way is using wp_enqueue_style() in a conditional way as described here:

http://core.trac.wordpress.org/ticket/10618#comment:6

function wpa85495_enqueue_style(){
    wp_enqueue_style('my-style', WP_PLUGIN_URL . '/my-plugin/style.css', false );
    global $wp_styles;
    $wp_styles->add_data( 'my-style', 'conditional', 'IE' );
}

add_action( 'wp_enqueue_scripts', 'wpa85495_enqueue_style' );

Answer 2

You want wp_enqueue_style(). It's considered best practice and all around more elegant than hooking into the wp_head.

http://codex.wordpress.org/Function_Reference/wp_enqueue_style