Are shortcodes case-sensitive?

1 comment

1. Short Answer

   Yes, shortcodes are case sensitive

   Longer Answer

   It’s really easy to build a test case for this and see.

   <?php
   add_shortcode('sOme_ShOrTcOdE', 'wpse102375_shortcode');
   function wpse102375_shortcode($args, $content=null)
   {
       return 'yep';
   }
   

   Longest Answer

   Read the source.

   The “magic” with shortcodes happens in do_shortcode, so let’s take a look at that.

   <?php
   // wp-includes/shortcode.php
   function do_shortcode($content) {
       global $shortcode_tags;
   
       if (empty($shortcode_tags) || !is_array($shortcode_tags))
           return $content;
   
       $pattern = get_shortcode_regex();
       return preg_replace_callback( "/$pattern/s", 'do_shortcode_tag', $content );
   }
   

   Hmmm, $shortcode_tags — probably get’s set up in add_shortcode:

   <?php
   // wp-includes/shortcodes.php
   function add_shortcode($tag, $func) {
       global $shortcode_tags;
   
       if ( is_callable($func) )
           $shortcode_tags[$tag] = $func;
   }
   

   So that’s just a key value part of $shortcode_name => $a_callablle. Makes sense.

   Looks like most of the magic of do_shortcode takes place in building the regular expression to match shortcodes themselves. All that happens in get_shortcode_regex, so let’s take a look there:

   <?php
   // wp-includes/shortcode.php
   function get_shortcode_regex() {
       global $shortcode_tags;
       $tagnames = array_keys($shortcode_tags);
       $tagregexp = join( '|', array_map('preg_quote', $tagnames) );
   
       // WARNING! Do not change this regex without changing do_shortcode_tag() and strip_shortcode_tag()
       // Also, see shortcode_unautop() and shortcode.js.
       return
             '\['                              // Opening bracket
           . '(\[?)'                           // 1: Optional second opening bracket for escaping shortcodes: [[tag]]
           . "($tagregexp)"                     // 2: Shortcode name
           . '(?![\w-])'                       // Not followed by word character or hyphen
           . '('                                // 3: Unroll the loop: Inside the opening shortcode tag
           .     '[^\]\/]*'                   // Not a closing bracket or forward slash
           .     '(?:'
           .         '\/(?!\])'               // A forward slash not followed by a closing bracket
           .         '[^\]\/]*'               // Not a closing bracket or forward slash
           .     ')*?'
           . ')'
           . '(?:'
           .     '(\/)'                        // 4: Self closing tag ...
           .     '\]'                          // ... and closing bracket
           . '|'
           .     '\]'                          // Closing bracket
           .     '(?:'
           .         '('                        // 5: Unroll the loop: Optionally, anything between the opening and closing shortcode tags
           .             '[^\[]*+'             // Not an opening bracket
           .             '(?:'
           .                 '\[(?!\/\2\])' // An opening bracket not followed by the closing shortcode tag
           .                 '[^\[]*+'         // Not an opening bracket
           .             ')*+'
           .         ')'
           .         '\[\/\2\]'             // Closing shortcode tag
           .     ')?'
           . ')'
           . '(\]?)';                          // 6: Optional second closing brocket for escaping shortcodes: [[tag]]
   }
   

   Very well commented in the core, so not much to explain here. The key part is here:

   global $shortcode_tags;
   $tagnames = array_keys($shortcode_tags);
   $tagregexp = join( '|', array_map('preg_quote', $tagnames) );
   

   Which essentially will get used later to explicitly match any of the registered shortcode names. Notice that no text processing is done other than preg_quote, so WP will only try to match the explicit values passed in to add_shortcode as the shortcode name. It’s looking like shortcodes are case sensitive so far.

   Next we need to take a look at the flags where the regular expression built in get_shortcode_regex is used. The relevant bit of do_shortcode.

   "/$pattern/s"
   

   The slashes delimit the regular expression, letters after the closing slash are PRCE flags or modifiers.

   If we saw an i there it would be case insensitive. We only have an s (meaning a . matches all characters including the newline).

   So, yes, shortcodes are case sensitive.

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