Thats what meta_boxes are for. First you need to register the metabox within the page or post with the function add_meta_box. Then you want to get that value with get_post_meta on the page where you want the “Source”.
This goes into your functions.php file:
/* Define the custom box */
add_action( 'add_meta_boxes', 'wpse_source_link' );
/* Do something with the data entered */
add_action( 'save_post', 'wpse_source_link_save' );
/* Adds a box to the main column on the Post and Page edit screens */
function wpse_source_link() {
add_meta_box(
'source_link',
__( 'Source-link', 'myplugin_textdomain' ),
'wpse_source_meta_box',
'post',
'side'
);
}
/* Prints the box content */
function wpse_source_meta_box( $post ) {
// Use nonce for verification
wp_nonce_field( plugin_basename( __FILE__ ), 'myplugin_noncename' );
// The actual fields for data entry
echo '<input type="text" id="source-link"" name="source_link" value="'. get_post_meta( $post->ID, '_source_link', true ) .'" size="25" />';
}
/* When the post is saved, saves our custom data */
function wpse_source_link_save( $post_id ) {
// verify if this is an auto save routine.
// If it is our form has not been submitted, so we dont want to do anything
if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
return;
// verify this came from the our screen and with proper authorization,
// because save_post can be triggered at other times
if ( ! wp_verify_nonce( $_POST['myplugin_noncename'], plugin_basename( __FILE__ ) ) )
return;
// Check permissions
if ( current_user_can( 'edit_post', $post_id ) ) {
update_post_meta( $post_id, '_source_link', $_POST['source_link'] );
}
}
This code register the meta_box and stores the value in post_meta as “_source_link”.
It will look like this:
Then you want to get the value in the post, Use get_post_meta:
<?php echo esc_url( get_post_meta( $post->ID, '_source_link', true ) ); ?>
You should read about:
add_meta_boxes,
update_post_meta and
get_post_meta