_SERVER['SERVER_SOFTWARE']: Apache/2.4.25 (Debian) PHP/5.6.40-0+deb8u2 OpenSSL/1.0.2u mod_apreq2-20090110/2.8.0 mod_perl/2.0.10 Perl/v5.24.1

_GET['show']: teststring
_SERVER['QUERY_STRING']: show=teststring

Some special characters like &, % and some escaped %2B and %26 et.c. works fine in a normal PHP string variable.