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To: zsh-workers@math.gatech.edu (Zsh hackers list)
Subject: $(nooutput) problem
Date: Tue, 28 May 1996 11:18:09 +0200
From: Peter Stephenson <pws@ifh.de>
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It seems care is needed: (1) if a command is not a simple one no
arguments may be necessary, so that having no arguments in execcmd()
is perfectly legal; (2) single word substitution needs to keeps its
arguments, for example the variable assignment code expects something
back from prefork(); (3) there's another bug/incompatibility (nearer
the latter than the former) resulting from the failure to delete empty
arguments:

% ksh -c 'cmd=; $cmd print foo'
foo
% zsh -fc 'cmd=; $cmd print foo'
zsh: permission denied: print

(which is certainly not the right answer in any case).

For these reasons I've fixed the problem by getting prefork() to junk
empty nodes if and only if it is not doing single word substitution,
and execcmd() to return if and only if it is a `simple' command with
no arguments.

*** Src/exec.c.empty	Fri May 17 16:25:20 1996
--- Src/exec.c	Tue May 28 10:35:36 1996
***************
*** 1200,1205 ****
--- 1200,1208 ----
      /* Do prefork substitutions */
      prefork(args, (((type == CCASE) ? 4 : 0) | (assign ? 2 : isset(MAGICEQUALSUBST))));
  
+     if (type == SIMPLE && empty(args))
+ 	return;
+ 
      /* Set up special parameter $_ */
      zsfree(underscore);
      if (nonempty(args) && (underscore = ztrdup((char *) getdata(lastnode(args)))))
*** Src/subst.c.empty	Tue May 28 10:34:04 1996
--- Src/subst.c	Tue May 28 10:41:15 1996
***************
*** 51,57 ****
  void
  prefork(LinkList list, int flags)
  {
!     LinkNode node;
  
      for (node = firstnode(list); node; incnode(node)) {
  	char *str, *str3;
--- 51,57 ----
  void
  prefork(LinkList list, int flags)
  {
!     LinkNode node, next;
  
      for (node = firstnode(list); node; incnode(node)) {
  	char *str, *str3;
***************
*** 69,77 ****
  	else if (!(node = stringsubst(list, node, flags & 4)))
  	    return;
      }
!     for (node = firstnode(list); node; incnode(node)) {
  	if (*(char *)getdata(node))
  	    remnulargs(getdata(node));
  	if (unset(IGNOREBRACES) && !(flags & 4))
  	    while (hasbraces(getdata(node)))
  		xpandbraces(list, &node);
--- 69,82 ----
  	else if (!(node = stringsubst(list, node, flags & 4)))
  	    return;
      }
!     for (node = firstnode(list); node; node = next) {
! 	next = nextnode(node);
  	if (*(char *)getdata(node))
  	    remnulargs(getdata(node));
+ 	else if (!(flags & 4)) {
+ 	    uremnode(list, node);
+ 	    continue;
+ 	}
  	if (unset(IGNOREBRACES) && !(flags & 4))
  	    while (hasbraces(getdata(node)))
  		xpandbraces(list, &node);


-- 
Peter Stephenson <pws@ifh.de>       Tel: +49 33762 77366
WWW:  http://www.ifh.de/~pws/       Fax: +49 33762 77330
Deutches Electronen-Synchrotron --- Institut fuer Hochenergiephysik Zeuthen
DESY-IfH, 15735 Zeuthen, Germany.