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Date: Tue, 29 Oct 2019 03:31:18 -0700 (PDT)
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Subject: Re: How to run external program pipeline and capture output
From: joakimds@kth.se
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Xref: reader01.eternal-september.org comp.lang.ada:57364
Date: 2019-10-29T03:31:18-07:00
List-Id: <comp.lang.ada>

Den m=C3=A5ndag 28 oktober 2019 kl. 18:24:41 UTC+1 skrev Alain De Vos:
> I like to run a command like :
> /usr/local/bin/zsh -c "/bin/ls | /usr/bin/grep a"
> But the procedure below produces no ouput,=20
>=20
> To make it strange, with /usr/local/bin/zsh -c "/bin/ls " it works fine.
>=20
> procedure System_Command is
>    Command    : String          :=3D "/usr/local/bin/zsh -c ""/bin/ls | /=
usr/bin/grep a""";
>    Args       : Argument_List_Access;
>    Status     : aliased Integer;
>    Separators : constant String :=3D LF & CR;
>    Reply_List : Slice_Set;
> begin
>    Ada.Text_IO.Put_Line (Command);
>    Args :=3D Argument_String_To_List (Command);
>    -- execute the system command and get the output in a single string
>    declare
>       Response : String :=3D
>         Get_Command_Output
>           (Command   =3D> Args (Args'First).all,
>            Arguments =3D> Args (Args'First + 1 .. Args'Last),
>            Input     =3D> "",
>            Status    =3D> Status'Access);
>    begin
>       Free (Args);
>       -- split the output in a slice for easier manipulation
>       if Status =3D 0 then
>          Create (S          =3D> Reply_List,
>                  From       =3D> Response,
>                  Separators =3D> Separators,
>                  Mode       =3D> Multiple);
>       end if;
>    end;
>    -- do something with the system output. Just print it out
>    for I in 1 .. Slice_Count (Reply_List) loop
>       Put_Line (Slice (Reply_List, I));
>    end loop;
> end System_Command;

In 2010 Gautier De Montmollin posted the following code snippet for executi=
ng terminal commands:

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

procedure Pipe_test is
   Command : constant String :=3D -- a command which should be long to
execute
      "gnatmake -f -Pbig_project.gpr";
   Pd      : Process_Descriptor;
   Args    : Argument_List_Access;
   Result  : Expect_Match;
begin
   Args :=3D Argument_String_To_List (Command);
   Non_Blocking_Spawn
      (Pd,
       Command     =3D> Args (Args'First).all,
       Args        =3D> Args (Args'First + 1 .. Args'Last),
       Buffer_Size =3D> 0);
   loop
      begin
         Expect (Pd, Result, Regexp =3D> "\n", Timeout =3D> 1_000);
         case Result is
            when Expect_Timeout =3D>
               Put("[timeout]"); -- no output for this time slice
            when Expect_Full_Buffer =3D>
               Put("[full]"); -- doesn't happen with buffer size =3D 0 ?
            when 1 =3D>
               Put(Expect_Out(Pd)); -- regexp matched
            when others =3D>
               Put("[?]"); -- shouldn't (and doesn't) happen
         end case;
      exception
         when Process_died =3D> Put("[died]"); exit;
      end;
   end loop;
   Put(Expect_Out(Pd));
   Close (Pd);
end Pipe_test;

Best regards,
Joakim