When I try to execte my script I get following error:

[root@ scripts]# su cactiuser perl unix_apachestats.pl localhost
perl: /usr/bin/perl: cannot execute binary file

I also tried

[root@ scripts]# su cactiuser unix_apachestats.pl localhost
unix_apachestats.pl: /bin/bash=/bin/bash: No such file or directory
unix_apachestats.pl: =/usr/bin/lynx: No such file or directory
unix_apachestats.pl: =/usr/bin/head: No such file or directory
unix_apachestats.pl: my: command not found
unix_apachestats.pl: chomp: command not found
unix_apachestats.pl: line 34: syntax error near unexpected token `{'
unix_apachestats.pl: line 34: `if ($hostname eq '') {'

In order to narrow the possible sources for this error, it might be a good idea to check the system log file, to see if there is a more detailed error message.

In a Debian system this file is located at /var/log/messages

Shortly after reproducing the error, display the newest lines in this usually very long file by typing:

(You need be root to have access to that file).

try su - cactiuser perl unix_apachestats.pl localhost

su by itself does not set environment variables needed by this script. call it with su - (the minus runs the environment scripts and sets the variables)..