Hi,
thanks for discovering the bug, I'm sorry that I did not find it during my tests. Regarding a possible solution, I have the following comment:
We could resolve it in 3 different files: extrahd.pl - which actually emits the output by a PRINT statement (line 51) which looks a little bit like a debug statement. Nevertheless, it might make sense that this file gives some output.
extrahdctrl.c - which only calls the extrahd.pl, but might be used by users in the commandline, so removing/redirecting the stdout could make sense, but still it might be that users actually expect output here. Alternatively, a --quiet option could be introduced here that suppresses the output.
extrahd.cgi - which is used by the web-frontend. Here, the "system" call could be exchanged with an "qx" call or backticks, which would maybe make it more explicit that we are not using stdout at this point. The commands could then be unchanged. I'm not a perl expert, so I'm not familiar if qx is preferred over system when the stdout should be ignored. In php, exec would be more appropriate, I suppose.
Best regards, Wolfgang