How can I display a desired date into a Wordpress page? - wordpress

Question

I'm trying to find a way to choose a date and display it into a Wordpress page.
Simply put, that's the way this may operate:
One or several pages are input a shortcode or a PHP code via PHP insert
An operator/webmaster chooses a date from let's say a calendar or drop down
This date (formatted) shows into the pages that have the shortcode/PHP code
I do not want automatic or current date which I can do with this plugin.
Can anybody help achieve this with a plugin or a PHP snippet?

Answer 1

Display a custom date field in Settings->Reading:
function wpse_52414489_custom_date() {
// Add the section to reading settings so we can add our
// fields to it
add_settings_section(
'eg_custom_settings',
'My custom settings',
'',
'reading'
);
// Add the field with the names and function to use for our new
// settings, put it in our new section
add_settings_field(
'eg_custom_date',
'My custom date',
'eg_custom_date_callback',
'reading',
'eg_custom_settings'
);
// Register our setting so that $_POST handling is done for us and
// our callback function just has to echo the <input>
register_setting( 'reading', 'eg_custom_date' );
}
function eg_custom_date_callback() {
echo '<input name="eg_custom_date" id="eg_custom_date" type="date" value="' . get_option( 'eg_custom_date' ) . '" class="code" /> Explanation text';
}
add_action( 'admin_init', 'wpse_52414489_custom_date' );
Add your shortcode (EDIT: custom date format):
add_filter( 'init', function() {
add_shortcode( 'my-custom-date', function() {
return date( 'd/m/Y', strtotime( get_option( 'eg_custom_date' ) ) );
});
});
Usage:
[my-custom-date]
Output:
2018-09-18