program open_example;
{ This program demonstrates the use of the open procedure. }
const
   name_of_file = 'open1.txt';
   file3 = '*Enter_a_filename-- ';
type
   char_array = varying [50] of char;
var
   infile: text;
   error: integer32;
   name: char_array;
begin
   { Open an existing file. }
   open(infile, name_of_file, 'old', error);
   if error = 0 then begin
     writeln('Opened ', name_of_file, ' for reading.');
     close(infile)
   end else
     writeln('Error opening file', name_of_file, error);
   { Open a file specified by a command line argument. }
   open(infile, '^1', 'unknown', error);
   if error = 0 then begin
     argv(1, name);
     writeln('Opened ', name, ' for reading.');
     close(infile)
   end else
     writeln('No command line argument; error code =', error);
   { Open a file that may or may not exist. }
   { Prompt user for name of file at runtime. }
   open(infile, file3, 'unknown', error);
   if error = 0 then begin
     writeln('Opened file for reading.');
     close(infile)
   end else
     writeln('Error opening file', error)
end. { open_example }