i/sysafe

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    /*
       SYSAFE.I

       Replacement for system function safe for use when Yorick gets huge.

       $Id$
     */
    /*    Copyright (c) 1996.  The Regents of the University of California.
                        All rights reserved.  */

    func sysafe (command)
    /* DOCUMENT sysafe, "command line"
             or system, "command line"
         pass the command line to a UNIX sh (Bourne) shell for execution.

         This requires a fork() system call, which in turn makes a copy of
         the yorick executable in virtual memory before replacing that copy
         with the sh shell.  If yorick has grown to enormous size, the copy

         can bring your machine to its knees or kill it.  If you include
         sysafe.i before yorick grows (before you start the calculation that
         requires the large data arrays), a pipe is opened to an sh which

         remains running, and the original system command is replaced by

         sysafe.  Future system commands will be piped to the already
         running sh, so no dangerous copy operation is required.

         There are four problems with this approach:

           (1) You can't run interactive programs with sysafe, because the
               stdin is from the pipe (sysafe_pipe) instead of the keyboard.
    	   Attempting to do so may lock up yorick.
           (2) Since the command runs asynchronously now, yorick can't wait
               until it completes, and yorick's prompt will often precede

    	   the output from the command, unlike using the default system
    	   function.
           (3) Some typographical errors in commands may kill the sh; since

               you don't start a new one each time, the system command will
    	   stop working.

           (4) The shorthand $ syntax still uses the dangerous system call;

               you need to call system as an ordinary function for sysafe
    	   to protect you.

       SEE ALSO: system_orig
     */
    {

      write, sysafe_pipe, format="%s\n", command;
      fflush, sysafe_pipe;
    }

    if (is_void(system_orig)) {
      sysafe_pipe= popen("sh", 1);
      system_orig= system;

      system= sysafe;
    }