Re: How to run external program pipeline and capture output

[joakimds@kth.se]

Den måndag 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, 
> 
> To make it strange, with /usr/local/bin/zsh -c "/bin/ls " it works fine.
> 
> procedure System_Command is
>    Command    : String          := "/usr/local/bin/zsh -c ""/bin/ls | /usr/bin/grep a""";
>    Args       : Argument_List_Access;
>    Status     : aliased Integer;
>    Separators : constant String := LF & CR;
>    Reply_List : Slice_Set;
> begin
>    Ada.Text_IO.Put_Line (Command);
>    Args := Argument_String_To_List (Command);
>    -- execute the system command and get the output in a single string
>    declare
>       Response : String :=
>         Get_Command_Output
>           (Command   => Args (Args'First).all,
>            Arguments => Args (Args'First + 1 .. Args'Last),
>            Input     => "",
>            Status    => Status'Access);
>    begin
>       Free (Args);
>       -- split the output in a slice for easier manipulation
>       if Status = 0 then
>          Create (S          => Reply_List,
>                  From       => Response,
>                  Separators => Separators,
>                  Mode       => 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 executing 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 := -- 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 := Argument_String_To_List (Command);
   Non_Blocking_Spawn
      (Pd,
       Command     => Args (Args'First).all,
       Args        => Args (Args'First + 1 .. Args'Last),
       Buffer_Size => 0);
   loop
      begin
         Expect (Pd, Result, Regexp => "\n", Timeout => 1_000);
         case Result is
            when Expect_Timeout =>
               Put("[timeout]"); -- no output for this time slice
            when Expect_Full_Buffer =>
               Put("[full]"); -- doesn't happen with buffer size = 0 ?
            when 1 =>
               Put(Expect_Out(Pd)); -- regexp matched
            when others =>
               Put("[?]"); -- shouldn't (and doesn't) happen
         end case;
      exception
         when Process_died => Put("[died]"); exit;
      end;
   end loop;
   Put(Expect_Out(Pd));
   Close (Pd);
end Pipe_test;

Best regards,
Joakim