my_program inputfile outputfile

##</code><code>##

my $whatever = <>; 

##</code><code>##

           while (<>) {
               ...                     # code for each line
           }

       is equivalent to the following Perl-like pseudo code:

           unshift(@ARGV, ’-’) unless @ARGV;
           while ($ARGV = shift) {
               open(ARGV, $ARGV);
               while (<ARGV>) {
                   ...         # code for each line
               }
           }