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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. 
1.a/2
Implementation defined: The meaning of Argument_Count, Argument, and Command_Name for package Command_Line. The bounds of type Command_Line.Exit_Status.

Static Semantics

2
The library package Ada.Command_Line has the following declaration: 
3
package Ada.Command_Line is
  pragma Preelaborate(Command_Line);
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  function Argument_Count return Natural;
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  function Argument (Number : in Positive) return String;
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  function Command_Name return String;
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  type Exit_Status is implementation-defined integer type;
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  Success : constant Exit_Status;
  Failure : constant Exit_Status;
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  procedure Set_Exit_Status (Code : in Exit_Status);
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private
  ... -- not specified by the language
end Ada.Command_Line;
11
function Argument_Count return Natural;
12
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.
13
function Argument (Number : in Positive) return String;
14
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. {Constraint_Error (raised by failure of run-time check)} If Number is outside the range 1..Argument_Count, then Constraint_Error is propagated. 
14.a
Ramification: If the external execution environment does not support passing arguments to a program, then Argument(N) for any N will raise Constraint_Error, since Argument_Count is 0.
15
function Command_Name return String;
16
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.
16.1/1
type Exit_Status is implementation-defined integer type;
17
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.
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procedure Set_Exit_Status (Code : in Exit_Status);
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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.
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{unspecified [partial]} If the external execution environment does not support returning an exit value from a program, then Set_Exit_Status does nothing. 

Implementation Permissions

21
An alternative declaration is allowed for package Command_Line if different functionality is appropriate for the external execution environment. 
NOTES
22
37  Argument_Count, Argument, and Command_Name correspond to the C language's argc, argv[n] (for n>0) and argv[0], respectively. 
22.a
To be honest: The correspondence of Argument_Count to argc is not direct — argc would be one more than Argument_Count, since the argc count includes the command name, whereas Argument_Count does not. 

Extensions to Ada 83

22.b
{extensions to Ada 83} This clause is new in Ada 95. 

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