A.15 The Package Command_Line
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.
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
The library package
Ada.Command_Line has the following declaration:
{
AI12-0241-1}
package Ada.Command_Line
with Preelaborate, Nonblocking, Global =>
in out synchronized is function Argument_Count
return Natural;
function Argument (Number :
in Positive)
return String;
function Command_Name
return String;
type Exit_Status
is implementation-defined integer type;
Success :
constant Exit_Status;
Failure :
constant Exit_Status;
procedure Set_Exit_Status (Code :
in Exit_Status);
private
... -- not specified by the language
end Ada.Command_Line;
function Argument_Count return Natural;
{
AI05-0264-1}
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.
function Argument (Number : in Positive) return String;
{
AI12-0259-1}
If the external execution environment supports passing arguments to a
program, then Argument returns an implementation-defined value with lower
bound 1 corresponding to the argument at relative position Number. If
Number is outside the range 1..Argument_Count, then Constraint_Error
is propagated.
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.
function Command_Name return String;
{
AI05-0264-1}
{
AI12-0259-1}
If the external execution environment supports passing arguments to a
program, then Command_Name returns an implementation-defined value with
lower bound 1 corresponding to the name of the command invoking the program;
otherwise, Command_Name returns the null string.
type Exit_Status is implementation-defined integer type;
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.
procedure Set_Exit_Status (Code : in Exit_Status);
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.
If the external execution environment does not
support returning an exit value from a program, then Set_Exit_Status
does nothing.
Implementation Permissions
An alternative declaration is allowed for package
Command_Line if different functionality is appropriate for the external
execution environment.
NOTE Argument_Count, Argument, and
Command_Name correspond to the C language's argc, argv[n] (for n>0)
and argv[0], respectively.
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
Wording Changes from Ada 2012
{
AI12-0259-1}
Correction: Defined the lower bound of functions Argument and
Command_Name. This could be inconsistent if someone depended on the lower
bound of these routines (and it wasn't 1), but such code was never portable
(even to later versions of the same implementation). Thus we don't document
it as an inconsistency.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
