Re: pass a argument to spawn

[Anh Vo <anhvofrcaus@gmail.com>]

On Monday, January 11, 2016 at 5:17:50 PM UTC-8, comicf...@gmail.com wrote:
> Hi , i'm trying to do a simple " ls -a " , on Ubuntu .
> 
> I tried to associate a string value , because :
> 
>    subtype Argument_List is String_List;
> 
> But it failed .
> 
> Anyway , i'm lost with all the types and subtypes in GNAT.OS_Lib and System.Strings .
> 
> So , i don't know how to proceed in the simplier way .
> 
> WITH GNAT.OS_Lib ;	USE GNAT.OS_Lib ;
> WITH Ada.Text_IO ;	USE Ada.Text_IO ;
> 
> procedure console_Ada is
> 
>     state_spawn : boolean ;
> 
>     arg : Argument_List ( 1..1 ) ;
>     -- here the value must be "-a" .
> 
> begin
> 
>     new_line ;
> 
>     put_line ( " Print of your files :") ;
> 
>     new_line ;
> 
> 	Spawn ( "/bin/ls" , arg , state_spawn );
>     -- /bin/ls -a
> 
>     new_line ;
> 
>     put ( " Execution of the program with Spawn ?  : " & Boolean'Image( state_spawn ) ) ;
> 
> end console_Ada ;

Why mess with low level while there is a simpler way. Here is a quick binding to the system call as shown below.

with Interfaces.C;

function Invoke_System (Name :string) return Integer is
	
   C_Name : constant Interfaces.C.Char_Array (1 .. Name'Length + 1) := 
		                                  Interfaces.C.To_C(Name);

   function C_system (Name : System.Address) return Interfaces.C.int;
   pragma Import(C, C_system, "system");

begin
   return integer (C_system(C_Name(1)'address));
end;

procedure Invoke_System (Name : String) is
   Dummy : Integer;
begin
   Dummy := Invoke_System(Name);
end Invoke_System;

--...

declare
   Unix_Command : constant String := "ls -a";
begin
   Invoke_System (Unix_Command);
end;

Anh Vo