gistfile1.php

<?php
// [gist id="ID" file="FILE"]
function gist_shortcode($atts) {
  return sprintf(
    '<script src="https://gist.github.com/%s.js%s"></script>', 
    $atts['id'], 
    $atts['file'] ? '?file=' . $atts['file'] : ''
  );
} add_shortcode('gist','gist_shortcode');

// Remove this function if you don't want autoreplace gist links to shortcodes
function gist_shortcode_filter($content) {
  return preg_replace('/https:\/\/gist.github.com\/([\da-f]+)[\.js\?]*[\#]*file[=|_]+([\w\.]+)(?![^<]*<\/a>)/i', '[gist id="${1}" file="${2}"]', $content );
} add_filter( 'the_content', 'gist_shortcode_filter', 9);
?>