Re: '>>' does not create file if set -C (noclobber) is active

[Peter Stephenson <p.w.stephenson@ntlworld.com>]

On Sun, 28 Jun 2015 02:02:05 +0200
Martijn Dekker <martijn@inlv.org> wrote:
> Peter Stephenson schreef op 27-06-15 om 19:02:
> > This isn't very elegant, but nor is it obviously problematic, and it
> > does at least draw attention to a potential issue.
> 
> I've tested this patch against the current git version and noticed the
> following:

Yep, I got throughly confused about the logic.  I think this is now
correct.

It doesn't have to have a name with CLOBBER in it, though it does have
to be related to NO_CLOBBER --- the whole point is to choose between
long-standing and documented zsh behaviour, and POSIX behaviour, when
you have NO_CLOBBER set.  You can now also make your own decision which
you want, and don't need to post messages to the list to tell us :-).
I've called it APPEND_CREATE.

diff --git a/Doc/Zsh/options.yo b/Doc/Zsh/options.yo
index 2371e35..833c975 100644
--- a/Doc/Zsh/options.yo
+++ b/Doc/Zsh/options.yo
@@ -1094,10 +1094,12 @@ pindex(NOCLOBBER)
 cindex(clobbering, of files)
 cindex(file clobbering, allowing)
 item(tt(CLOBBER) (tt(PLUS()C), ksh: tt(PLUS()C)) <D>)(
-Allows `tt(>)' redirection to truncate existing files,
-and `tt(>>)' to create files.
-Otherwise `tt(>!)' or `tt(>|)' must be used to truncate a file,
-and `tt(>>!)' or `tt(>>|)' to create a file.
+Allows `tt(>)' redirection to truncate existing files.
+Otherwise `tt(>!)' or `tt(>|)' must be used to truncate a file.
+
+If the option is not set, and the option tt(APPEND_CREATE) is also
+not set, `tt(>>!)' or `tt(>>|)' must be used to create a file.
+If either option is set, `tt(>>)' may be used.
 )
 pindex(CORRECT)
 pindex(NO_CORRECT)
@@ -1792,6 +1794,21 @@ enditem()
 
 subsect(Shell Emulation)
 startitem()
+pindex(APPEND_CREATE
+pindex(NO_APPEND_CREATE)
+pindex(APPENDCREATE)
+pindex(NOAPPENDCREATE)
+cindex(clobbering, POSIX compatibility)
+cindex(file clobbering, POSIX compatibility)
+cindex(no clobber, POSIX compatible)
+item(tt(APPEND_CREATE) <K> <S>)(
+This option only applies when tt(NO_CLOBBER) (-tt(C)) is in effect.
+
+If this option is not set, the shell will report an error when a
+append redirection (tt(>>)) is used on a file that does not already
+exists (the traditional zsh behaviour of tt(NO_CLOBBER)).  If the option
+is set, no error is reported (POSIX behaviour).
+)
 pindex(BASH_REMATCH)
 pindex(NO_BASH_REMATCH)
 pindex(BASHREMATCH)
diff --git a/Src/exec.c b/Src/exec.c
index 39d1326..960601f 100644
--- a/Src/exec.c
+++ b/Src/exec.c
@@ -3315,7 +3315,8 @@ execcmd(Estate state, int input, int output, int how, int last1)
 		    fil = -1;
 		else if (IS_APPEND_REDIR(fn->type))
 		    fil = open(unmeta(fn->name),
-			       (unset(CLOBBER) && !IS_CLOBBER_REDIR(fn->type)) ?
+			       ((unset(CLOBBER) && unset(APPENDCREATE)) &&
+				!IS_CLOBBER_REDIR(fn->type)) ?
 			       O_WRONLY | O_APPEND | O_NOCTTY :
 			       O_WRONLY | O_APPEND | O_CREAT | O_NOCTTY, 0666);
 		else
diff --git a/Src/options.c b/Src/options.c
index da3d830..320f46b 100644
--- a/Src/options.c
+++ b/Src/options.c
@@ -110,6 +110,7 @@ static struct optname optns[] = {
 {{NULL, "chaselinks",	      OPT_EMULATE},		 CHASELINKS},
 {{NULL, "checkjobs",	      OPT_EMULATE|OPT_ZSH},	 CHECKJOBS},
 {{NULL, "clobber",	      OPT_EMULATE|OPT_ALL},	 CLOBBER},
+{{NULL, "appendcreate",	      OPT_EMULATE|OPT_BOURNE},	 APPENDCREATE},
 {{NULL, "combiningchars",     0},			 COMBININGCHARS},
 {{NULL, "completealiases",    0},			 COMPLETEALIASES},
 {{NULL, "completeinword",     0},			 COMPLETEINWORD},
diff --git a/Src/zsh.h b/Src/zsh.h
index ce9b979..183620f 100644
--- a/Src/zsh.h
+++ b/Src/zsh.h
@@ -2120,6 +2120,7 @@ enum {
     CHASELINKS,
     CHECKJOBS,
     CLOBBER,
+    APPENDCREATE,
     COMBININGCHARS,
     COMPLETEALIASES,
     COMPLETEINWORD,