# the values here don't matter, all we really 
# care about is the existence of the keys
my %pro = map { $_, 1 }
            qw[CMD /bin/sh rds SysExec /oasis/bin/sysmenu 
               /oasis/bin/TS_TextSrvcs];

# get the third column from every line of $syscmd
my @list = map { (split " ")[3] } <$syscmd>;

# remove the keys of %pro in @list
delete @pro{@list}; 

# print the error message
foreach my $not_found (keys %pro) {
  print "Didn't find $not_found in output of system cmd.\n";
}