Re: Passing a Command to Unix in Ada

["David C. Hoos, Sr." <david.c.hoos.sr@ada95.com>]

Robert T. Sagris wrote in message <36BCB222.EF9B4FF7@physics.BLAH.purdue.BLAH.edu>...
>I was wondering if there are any functions similar to the system
>command in C available in Ada. Also I was wondering if there was
>a similar function as rename in Ada.
>
>If you could give a translation for the following lines it would be
>most appreciated. *THIS IS NOT HOMEWORK* I am trying to rewrite a little
>program I wrote in C to Ada but don't no were to look. I have looked
>through Ada, as a Second Language by Cohen and found nothing
>useful for this problem
>

Here is a library function which interfaces to the C library "system" function, followed by a little test program to execute it.

This should serve to illustrate how to interface to _any_ C library function.

Strictly speaking, this technique does not "pass a command to Unix" -- rather it interfaces to the C library.  In the case of
Execute_Shell_Command which interfaces to the C "System" command, I gave it the name I did for two reasons, viz.:

    1.  The name "System" cannot be used in Ada for a
        user-defined entity, because it's a language-defined
        package.

    2.  The name Execute_Shell_Command is more descriptive
        of what it actually does.  In some contexts, a program
        which executes a shell command is considered a security
        risk, so I make what it's doing more obvious.

---- begin Ada source code ----
with Ada.Characters.Latin_1;
with System;
function Execute_Shell_Command
           (The_Command : String) return Integer is
   function Execute
              (The_Command_Address : System.Address) return Integer;
   pragma Import (C, Execute, "system");
   The_Nul_Terminated_Command_String : constant String :=
     The_Command & Ada.Characters.Latin_1.Nul;
begin
   return Execute (The_Nul_Terminated_Command_String'Address);
end Execute_Shell_Command;
with Ada.Command_Line;
with Ada.Text_Io;
with Execute_Shell_Command;
procedure Test_Execute_Shell_Command is
   Status : Integer;
begin
   Ada.Text_Io.Put_Line
     ("Program """ & Ada.Command_Line.Command_Name &
      """ is executing the shell command """ &
      Ada.Command_Line.Argument (1) & """");
   Status := Execute_Shell_Command (Ada.Command_Line.Argument (1));
   Ada.Text_Io.Put_Line
     ("Function "" Execute_Shell_Command"" returned" &
      Integer'Image (Status));
end Test_Execute_Shell_Command;
---- end Ada source code ----