my $syntax = "
    syntax:  $0  <specfile> <data_in> <data_out> <logfile> <max errors>

    The purpose of this program is ...

";

(my $spec_file     = shift) or die $syntax;
(my $data_in_file  = shift) or die $syntax;
(my $data_out_file = shift) or die $syntax;
# etc...