Shortcode to output the value of a constant. e.g. [fe_constant_test constant="DB_HOST"]

shortcode_fe_constant_test.php

<?php
/**
 * Shortcode [fe_constant_test], which takes one parameter called "constant"
 * This shortcode then outputs the value of that constant.
 * I find this helpful when testing the value of constants with a complex
 * constant assignment (e.g. using .env)
 *
 * Example usage: [fe_constant_test constant="DB_HOST"]
 * outputs the following on my local development environment
 * Constant DB_HOST is defined as "localhost"
 *
 * Sal Ferrarello
 * http://salferrarello.com/
 * http://twitter.com/salcode
 * 
 * This can be added by navigating to the `mu-plugins` directory and running the following from the command line
 * curl -O https://gist.githubusercontent.com/salcode/72d43b2104b4ef8fb75f/raw/b741e2d5b2c45da80286e6fd772a59f414dfa8fa/shortcode_fe_constant_test.php
 */

add_shortcode( 'fe_constant_test', 'shortcode_fe_constant_test' );

function shortcode_fe_constant_test( $atts ) {
	shortcode_atts(
		array(
			'constant' => false,
		),
		$atts,
		'fe_constant_test'
	);

	if ( false === $atts['constant'] ) {
		return 'no constant was specified as shortcode parameter';
	}

	$constant_name = $atts['constant'];
	if ( ! defined( $constant_name ) ) {
		return "Constant {$constant_name} is undefined";
	}

	$constant_value = constant( $constant_name );
	return "Constant {$constant_name} is defined as \"{$constant_value}\"";
}