site_url();
bloginfo("wpurl"); //check this!

Returns Root Domain URL without trailing slash.

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home_url();

Returns URL of the WordPress Home target without trailing slash. Usually is the same as the root domain, but needn’t be!

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admin_url();

Returns the URL leading to the WP Admin directory including trailing slash.

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includes_url();

Returns the WP includes URL with trailing slash.

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content_url();

Returns the URL leading to the WP content directory.

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plugins_url();

Returns the URL leading to the WP plugin directory.

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dirname(get_bloginfo('stylesheet_url'));

Returns current active theme directory without trainling slash.

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bloginfo("stylesheet_url");

Returns path to current main Stylesheet.

bloginfo("template_url");
get_template_directory_uri();
bloginfo("template_directory");

Returns the current main template url without trailing slash.

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array_pop(array_filter(explode("/", $_SERVER['REQUEST_URI']), function ($val){return (strlen($val) > 0);}));

Return the last URL Slug that contains characters without leading or trailing slashes.