Trying to execute a command from inside of Ada

Trying to execute a command from inside of Ada

[John Smith]

Hello,

I found the following example:

http://rosettacode.org/wiki/Execute_a_system_command#Ada

And this is how I tried to adapt it to Linux:





with Interfaces.C;

with Ada.Text_IO;     use Ada.Text_IO;
with GNAT.OS_Lib;     use GNAT.OS_Lib;

procedure Sys_Command is
   Result    : Integer;
   Arguments : Argument_List :=
                 (  1=> new String'("bash"),
                    2=> new String'("ls -l ~")
                 );
begin
   Spawn
   (  Program_Name           => "bash",
      Args                   => Arguments,
      Output_File_Descriptor => Standout,
      Return_Code            => Result
   );
   for Index in Arguments'Range loop
      Free (Arguments (Index)); -- Free the argument list
   end loop;
end Sys_Command;




The problem is that 'ls -l ~' is not executed correctly.  I don't see any out put at all.  What am I doing wrong?

Re: Trying to execute a command from inside of Ada

[ytomino]

On Monday, June 4, 2018 at 12:17:32 PM UTC+9, John Smith wrote:
> Hello,
> 
> I found the following example:
> 
> http://rosettacode.org/wiki/Execute_a_system_command#Ada
> 
> And this is how I tried to adapt it to Linux:
> 
> 
> 
> 
> 
> with Interfaces.C;
> 
> with Ada.Text_IO;     use Ada.Text_IO;
> with GNAT.OS_Lib;     use GNAT.OS_Lib;
> 
> procedure Sys_Command is
>    Result    : Integer;
>    Arguments : Argument_List :=
>                  (  1=> new String'("bash"),
>                     2=> new String'("ls -l ~")
>                  );
> begin
>    Spawn
>    (  Program_Name           => "bash",
>       Args                   => Arguments,
>       Output_File_Descriptor => Standout,
>       Return_Code            => Result
>    );
>    for Index in Arguments'Range loop
>       Free (Arguments (Index)); -- Free the argument list
>    end loop;
> end Sys_Command;
> 
> 
> 
> 
> The problem is that 'ls -l ~' is not executed correctly.  I don't see any out put at all.  What am I doing wrong?

"-c" switch is needed for bash to pass the subcommand.
Try to compare them in your interactive shell.

$ bash "ls -l ~"
$ bash -c "ls -l ~"

Re: Trying to execute a command from inside of Ada

[Jacob Sparre Andersen]

John Smith wrote:

> procedure Sys_Command is
>    Result    : Integer;
>    Arguments : Argument_List :=
>                  (  1=> new String'("bash"),
>                     2=> new String'("ls -l ~")
>                  );

Have you tried to run this on your command line?

   bash "ls -l ~"

That's basically what you ask your program to do.

I would:

1) Avoid involving Bash in this.
2) Remember to pass each argument separately.

And I might additionally:

3) Expand "~" myself, as "ls" doesn't know how to do that (but
   "system()" or "/bin/sh" might).

Greetings,

Jacob
-- 
"Universities are not part of the nation's security organisation,
 they are not the nation's research laboratory either: they are
 the nation's universities."                     -- E.W. Dijkstra