[v1.1] add &>>foo as a shorthand for >>foo 2>&1 (re: 921bbca)

This is the 'append' variant of &>. It is very simple to add with
a little code in the lexer (lex.c); all we need to do is xor SYMREP
into the token to signify that the > is repeated. The parser will
then do the right thing without modification.

&>> msut be disabled in the POSIX compatibility mode for the same
reason as &> because, POSIXly,
	somecommand &>>somefile
is the same as
	somecommand &
	>>somefile
so it's a syntactical incompatibility. It's not one that's likely
to cause problems in real-life scripts, but better safe than sorry.

ANNOUNCE

@@ -19,6 +19,9 @@ New command line editor features:
 
 New shell language features:
 
+- The appending redirection operator &>>FILE is now available. It is a
+  shorthand for: >>FILE 2>&1
+
 - The 'time' reserved word now outputs timings in a precision of 3 digits
   after the decimal point if the TIMEFORAMT variable is not set. See also
   TIMEFORMAT under 'New features in shell variables' below.

NEWS

@@ -4,6 +4,9 @@ Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 
 2024-12-05:
 
+- [v1.1] The appending redirection operator &>>FILE is now available
+  (inspired by bash 4.0 and later). It is a shorthand for: >>FILE 2>&1
+
 - Fixed an issue in the vi line editors where lines beginning with whitespace
   could not be recalled from the history (e.g. with arrow up). Bug introduced
   on 2022-10-31.

src/cmd/ksh93/sh.1

@@ -3926,10 +3926,11 @@ for reading and store
 the file descriptor number in variable
 .BR n .
 .PP
-A special shorthand redirection operator \fB&>\fR\fIword\fR is available; it
-is equivalent to \fB>\fR\fIword\fR\fB 2>&1\fR. It cannot be preceded by any
-digit or variable name. This shorthand is disabled if the \fBposix\fR shell
-option is active.
+Special shorthand redirection operators \fB&>\fR\fIword\fR and
+\fB&>>\fR\fIword\fR are available; they are equivalent to
+\fB>\fR\fIword\fR\fB 2>&1\fR and \fB>\fR\fIword\fR\fB 2>&1\fR, respectively.
+They cannot be preceded by any digit or variable name. These shorthands are
+disabled if the \fBposix\fR shell option is active.
 .PP
 The order in which redirections are specified is significant.
 The shell evaluates each redirection in terms of the
@@ -8065,7 +8066,7 @@ and
 to open file descriptors > 2 without the close-on-exec flag,
 so that they are left open when invoking another program;
 .IP \[bu]
-disables the \fB&>\fR redirection shorthand;
+disables the \fB&>\fR and \fB&>>\fR redirection shorthands;
 .IP \[bu]
 disables fast filescan loops of type
 \f3while\fP \f2inputredirection\^\fP \f3;do\fP \f2list\^\fP \f3;done\fP;

src/cmd/ksh93/sh/lex.c

@@ -521,6 +521,12 @@ int sh_lex(Lex_t* lp)
 							/* bash-style "&>file" shorthand for ">file 2>&1" */
 							lp->digits = -1;
 							c = '>';
+							/* bash 4.0-style "&>>file" shorthand for ">>file 2>&1" */
+							fcgetc();
+							if(fcpeek(0)==c)
+								c |= SYMREP;
+							else
+								fcseek(-1);
 						}
 						else if(n=='|')
 							c |= SYMPIPE;

src/cmd/ksh93/tests/posix.sh

@@ -130,17 +130,32 @@ got=$(set --noposix; redirect 3>&1; "$SHELL" -c 'echo ok >&3' 2>/dev/null)
 [[ $got == "$exp" ]] || err_exit "file descriptor 3 left open in --noposix mode" \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 
-# disables the &> redirection shorthand;
+# disables the &> and &>> redirection shorthands;
 exp=''
 (set --posix; eval 'echo output &>out') >/dev/null
 got=$(<out)
 [[ $got == "$exp" ]] || err_exit "&> redirection shorthand not disabled in --posix mode" \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+(set --posix; eval 'echo output &>>out') >/dev/null
+got=$(<out)
+[[ $got == "$exp" ]] || err_exit "&>> redirection shorthand not disabled in --posix mode" \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 (set --noposix; eval 'echo output &>out') >/dev/null
 exp='output'
 got=$(<out)
 [[ $got == "$exp" ]] || err_exit "&> redirection shorthand disabled in --noposix mode" \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+case ${.sh.version} in
+*93u+m/1.0.*)
+	;;
+*)	# &>> available as of 93u+m/1.1
+	(set --noposix; eval 'echo MOAR &>>out') >/dev/null
+	exp+=$'\nMOAR'
+	got=$(<out)
+	[[ $got == "$exp" ]] || err_exit "&>> redirection shorthand disabled in --noposix mode" \
+		"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+	;;
+esac
 
 # disables fast filescan loops of type 'while inputredirection; do list; done';
 printf '%s\n' "un duo tres" >out