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

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

This isn't very elegant, but nor is it obviously problematic, and it
does at least draw attention to a potential issue.

pws

diff --git a/Doc/Zsh/options.yo b/Doc/Zsh/options.yo
index 2371e35..6dd2239 100644
--- a/Doc/Zsh/options.yo
+++ b/Doc/Zsh/options.yo
@@ -1819,6 +1819,20 @@ Make the tt(echo) builtin compatible with the BSD manref(echo)(1) command.
 This disables backslashed escape sequences in echo strings unless the
 tt(-e) option is specified.
 )
+pindex(CLOBBER_APPEND)
+pindex(NO_CLOBBER_APPEND)
+pindex(CLOBBERAPPEND)
+pindex(NOCLOBBERAPPEND)
+cindex(clobbering, POSIX compatibility)
+cindex(file clobbering, POSIX compatibility)
+cindex(no clobber, POSIX compatible)
+item(tt(CLOBBER_APPEND) <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.  If the option is set, no error is reported.
+)
 pindex(CONTINUE_ON_ERROR)
 pindex(NO_CONTINUE_ON_ERROR)
 pindex(CONTINUEONERROR)
diff --git a/Src/exec.c b/Src/exec.c
index 50a11eb..4ddfdf4 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) || isset(CLOBBERAPPEND)) &&
+				!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..3a0c838 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, "clobberappend",      OPT_EMULATE|OPT_BOURNE},	 CLOBBER},
 {{NULL, "combiningchars",     0},			 COMBININGCHARS},
 {{NULL, "completealiases",    0},			 COMPLETEALIASES},
 {{NULL, "completeinword",     0},			 COMPLETEINWORD},
diff --git a/Src/zsh.h b/Src/zsh.h
index ce9b979..05efa5f 100644
--- a/Src/zsh.h
+++ b/Src/zsh.h
@@ -2120,6 +2120,7 @@ enum {
     CHASELINKS,
     CHECKJOBS,
     CLOBBER,
+    CLOBBERAPPEND,
     COMBININGCHARS,
     COMPLETEALIASES,
     COMPLETEINWORD,