or download this
SV mysv = newSVpv("");
SvGROW(mysv, 1024); // preallocate 1024 bytes as buffer for the re
+sponse
sv_setpv("Hello World\0");
some_systemcall_with_the_message_buffer( SvPV(mysv), 1024); // wri
+tes the response into mysv and expects 1024 bytes to be writable