Object-oriented Software in Ada 95

34 Ada introduction: Part 1
If the program echo is compiled with the package Ada.Command_Line then the programmer has available the
following function calls:
call of function
Argument_Count
Argument(1)
Argument(2)
Note:
Returns
The number of command line arguments. In this case,
two.
A string representing the first command line argument.
In this case “Hello”.
A string representing the second command line
argument. In this case “there!”.
It would be an error detected at run-time to access argument(3).
The code for the program echo is as follows:
with Ada.Text_Io, Ada.Command_Line;
use Ada.Text_Io, Ada.Command_Line;
procedure Echo is
begin
for I in 1 .. Argument_Count loop --For each argument
Put( Argument(I) ); -- Print it
if I /= Argument_Count then -- If not last
Put(" "); -- Print separator
end if;
end loop;
New_Line;
end Echo;
Note:
See how the package Ada.Command_Line has been used here.
3.10.1 Putting it all together
If compiled to the executable file echo, the program could be run on a Unix or MSDOS system to implement the
command echo as follows:
% echo Hello there!
Which when run would write:
Hello there!
3.11 A better cat program
By using, the package Ada.Command_line a better version of the cat program can be written. In this new
version the files to be listed to the terminal are specified after the executable program name.
The following procedures and functions are used to control the reading of data from a file.
Function/Procedure
Open
Close
Effect
Opens an existing file. A file descriptor to this file is
returned as the result. A file descriptor is of type:
File_type in the package Ada.Text_Io.
Close the open file.
© M A Smith - May not be reproduced without permission