/*  $Id: pipe.pl,v 1.1 2000/10/09 10:18:32 jan Exp $

    Part of SWI-Prolog

    Author:  Jan Wielemaker
    E-mail:  jan@swi.psy.uva.nl
    WWW:     http://www.swi.psy.uva.nl/projects/SWI-Prolog/
    Copying: GPL-2.  See the file COPYING or http://www.gnu.org

    Copyright (C) 1990-2000 SWI, University of Amsterdam. All rights reserved.
*/

:- module(subcommand,
          [ pipe_through_command/3      % +Command, +In, -Out
          ]).
:- use_module(library(unix)).

%       pipe_through_command(+Command, +In, -Out)
%
%       Pipe text In through command Command and put the output of command
%       in Out.
%
%       Example:
%
%               ?- pipe_through_command(tr('a-z', 'A-Z'), hello, X)
%
%               X = 'HELLO'

pipe_through_command(Command, In, Out) :-
        pipe(ChildIn, MeOut),
        pipe(MeIn,  ChildOut),
        fork(Pid),
        (   Pid == child,
            close(MeOut),
            close(MeIn),
            dup(ChildIn, 0),
            dup(ChildOut, 1),
            close(ChildIn),
            close(ChildOut),
            exec(Command)
        ;   close(ChildIn),
            close(ChildOut),
            write(MeOut, In),
            close(MeOut),
            read_input(MeIn, Out),
            close(MeIn),
            wait(Pid, _Status)          % avoid zombi
        ).


read_input(In, Atom) :-
        get_code(In, C0),
        read_input(C0, In, Codes),
        atom_codes(Atom, Codes).

read_input(-1, _, []) :- !.
read_input(C, In, [C|T]) :-
        get_code(In, C1),
        read_input(C1, In, T).

