From c607c48c84dc29b994d397bc31c8bd6fe6a9201b Mon Sep 17 00:00:00 2001
From: Martijn Dekker <martijn@inlv.org>
Date: Tue, 1 Sep 2020 08:36:28 +0100
Subject: [PATCH] Revert <> redir FD except in posix mode (re: eeee77ed,
 60516872)

eeee77ed implemented a POSIX compliance fix that caused a potential
incompatibility with existing ksh scripts; it made the (rarely
used) read/write redirection operator, <>, default to file
descriptor 0 (standard input) as POSIX specified, instead of 1
(standard output) which is traditional ksh93 behaviour. So ksh
scripts needed to change all <> to 1<> to override the new default.

This commit reverts that change, except in the new posix mode.

src/cmd/ksh93/sh/lex.c:
- Make FD for <> default to 0 in POSIX mode, 1 otherwise.

src/cmd/ksh93/tests/io.sh:
- Revert <> regression test changes from 60516872; we no longer
  need 1<> instead of <> in ksh code.
---
 NEWS                      | 3 +++
 src/cmd/ksh93/sh.1        | 4 +++-
 src/cmd/ksh93/sh/lex.c    | 2 +-
 src/cmd/ksh93/tests/io.sh | 6 +++---
 4 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/NEWS b/NEWS
index 003ea1148..81f04f079 100644
--- a/NEWS
+++ b/NEWS
@@ -17,6 +17,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
   * causes the 'let' arithmetic command to recognise octal numbers by
     leading zeros regardless of the setting of the 'letoctal' option
   * causes file descriptors > 2 to be left open when invoking another program
+  * makes the <> redirection operator default to stdin instead of stdout
+    (this keeps the 2020-05-13 BUG_REDIRIO fix for the POSIX mode while
+    restoring traditional ksh93 behaviour for backwards compatibility)
 
 2020-08-19:
 
diff --git a/src/cmd/ksh93/sh.1 b/src/cmd/ksh93/sh.1
index 9e5bfcd3a..31e1f1406 100644
--- a/src/cmd/ksh93/sh.1
+++ b/src/cmd/ksh93/sh.1
@@ -3423,7 +3423,8 @@ otherwise, the file is created.
 Open file
 .I word\^
 for reading and writing
-as standard input.
+as standard output.
+If the \fBposix\fR option is active, it defaults to standard input instead.
 .TP
 .BI <>; word
 The same as
@@ -7040,6 +7041,7 @@ to fail or zero if no command has failed.
 Enable POSIX standard compatibility mode. This option
 is on by default if ksh is invoked as \fBsh\fR. It
 causes file descriptors > 2 to be left open when invoking another program,
+makes the \fB<>\fR redirection operator default to standard input,
 enables octal numbers in \fBlet\fR shell arithmetic (see \fBletoctal\fR), and
 disables the \fB&>\fR redirection shorthand.
 .TP 8
diff --git a/src/cmd/ksh93/sh/lex.c b/src/cmd/ksh93/sh/lex.c
index 0988802d8..54507541c 100644
--- a/src/cmd/ksh93/sh/lex.c
+++ b/src/cmd/ksh93/sh/lex.c
@@ -601,7 +601,7 @@ int sh_lex(Lex_t* lp)
 						c  |= SYMPIPE;
 					else if(c=='<' && n=='>')
 					{
-						lp->digits = 0;
+						lp->digits = sh_isoption(SH_POSIX) ? 0 : 1;
 						c = IORDWRSYM;
 						fcgetc(n);
 						if(fcgetc(n)==';')
diff --git a/src/cmd/ksh93/tests/io.sh b/src/cmd/ksh93/tests/io.sh
index f703e2c4a..5aab5dc36 100755
--- a/src/cmd/ksh93/tests/io.sh
+++ b/src/cmd/ksh93/tests/io.sh
@@ -304,14 +304,14 @@ fi
 $SHELL -c 'exec 3<>; /dev/null'  2> /dev/null && err_exit '<>; with exec should be an error'
 $SHELL -c ': 3<>; /dev/null'  2> /dev/null || err_exit '<>; not working with at all'
 print $'hello\nworld' > $tmp/1
-if      ! $SHELL -c "false 1<>; $tmp/1"  2> /dev/null
+if      ! $SHELL -c "false <>; $tmp/1"  2> /dev/null
 then    [[ $(<$tmp/1) == $'hello\nworld' ]] || err_exit '<>; not preserving file on failure'
 fi
-if	! $SHELL -c "head -1 $tmp/1" 1<>; $tmp/1  2> /dev/null
+if	! $SHELL -c "head -1 $tmp/1" <>; $tmp/1  2> /dev/null
 then	[[ $(<$tmp/1) == hello ]] || err_exit '<>; not truncating file on success of head'
 fi
 print $'hello\nworld' > $tmp/1
-if	! $SHELL -c head  < $tmp/1 <#((6)) 1<>; $tmp/1  2> /dev/null
+if	! $SHELL -c head  < $tmp/1 <#((6)) <>; $tmp/1  2> /dev/null
 then	[[ $(<$tmp/1) == world ]] || err_exit '<>; not truncating file on success of behead'
 fi