It's shocking how many of these upvoted/accepted answers are incomplete, so they don't answer the OP's question, after 7 years!
If you are on a page with URL like: http://example.com/directory/file.php?paramater=value
...and you would like to return just: http://example.com/directory/file.php
then use:
echo $_SERVER['REQUEST_SCHEME'].'://'.$_SERVER['SERVER_NAME'].$_SERVER['PHP_SELF'];