A.15 The Package Command_Line

1. The package Command_Line allows a program to obtain the values of its arguments and to set the exit status code to be returned on normal termination.
   Static Semantics
   
2. The library package Ada.Command_Line has the following declaration:

3. package Ada.Command_Line is
     pragma Preelaborate(Command_Line);
   

4.   function Argument_Count return Natural;
   

5.   function Argument (Number : in Positive) return String;
   

6.   function Command_Name return String;
   

7.   type Exit_Status is implementation-defined integer type;
   

8.   Success : constant Exit_Status;
     Failure : constant Exit_Status;
   

9.   procedure Set_Exit_Status (Code : in Exit_Status);
   

10. private
      ... -- not specified by the language
    end Ada.Command_Line;
    

11. function Argument_Count return Natural;
    

    1. If the external execution environment supports passing arguments to a program, then Argument_Count returns the number of arguments passed to the program invoking the function. Otherwise it returns 0. The meaning of "number of arguments" is implementation defined.

1. function Argument (Number : in Positive) return String;
   

   1. If the external execution environment supports passing arguments to a program, then Argument returns an implementation-defined value corresponding to the argument at relative position Number. If Number is outside the range 1..Argument_Count, then Constraint_Error is propagated.

1. function Command_Name return String;
   

   1. If the external execution environment supports passing arguments to a program, then Command_Name returns an implementation-defined value corresponding to the name of the command invoking the program; otherwise Command_Name returns the null string.
   2. The type Exit_Status represents the range of exit status values supported by the external execution environment. The constants Success and Failure correspond to success and failure, respectively.

1. procedure Set_Exit_Status (Code : in Exit_Status);
   

   1. If the external execution environment supports returning an exit status from a program, then Set_Exit_Status sets Code as the status. Normal termination of a program returns as the exit status the value most recently set by Set_Exit_Status, or, if no such value has been set, then the value Success. If a program terminates abnormally, the status set by Set_Exit_Status is ignored, and an implementation-defined exit status value is set.
   2. If the external execution environment does not support returning an exit value from a program, then Set_Exit_Status does nothing.

1. An alternative declaration is allowed for package Command_Line if different functionality is appropriate for the external execution environment.
   

   NOTES
   

2. (36) Argument_Count, Argument, and Command_Name correspond to the C language's argc, argv[n] (for n>0) and argv[0], respectively.

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