How can I print my own error message instead of the one above if the command is not found?

How about something like this:

:
:
:  much hand waving....
:
my $output="";
eval "
         $output=`my_command -v`;
     ";
if ($@){
    print "it broke!\n";
} else {
   : whatever...
}
[download]

disclaimer: completely untested and I don't know what's in "my_command".