If elseif else shortcode example

functions.php

<?php
// See this comment: https://www.nathankowald.com/blog/2019/06/wordpress-shortcode-if-elseif-else-statements/comment-page-1/#comment-222167

/**
 * Add this code into your theme's functions.php file (or custom plugin).
 */

add_filter( 'query_vars', function( $vars ) {
	// Add any other $_GET params you want to use.
	$vars[] = 'paramName';

	return $vars;
});

function param_is( $param_name, $val ) {
	return $val === get_query_var( $param_name );
}

add_filter( 'if_elseif_else_shortcode_allowed_callables', function( $whitelist ) {
	$whitelist[] = 'param_is';

	return $whitelist;
});

/* Shortcodes to use:
[if param_is paramName value1]
text option #1
[elseif param_is paramName value2]
text option #2
[else]
text option #3
[/if]
*/

When you don't want to whitelist every GET parameter:

function param_is( $param_name, $val ) {
	return isset($_GET[$param_name]) && $_GET[$param_name] === $val;
}

There should be a tailing ; after the last add_filter() call, when we are not using a closing ?> tag: https://stackoverflow.com/a/29284131/13765033

Thanks David. I've updated the gist.