Avoid AIX 6.1 ksh88 ECHO_C command substitution bug.

* lib/m4sugar/m4sh.m4 (_AS_ECHO_N_PREPARE): Ensure more than
one character is output with `\c'; reset echo output state
if buggy ksh was detected, and set ECHO_T instead of ECHO_C.
* doc/autoconf.texi (Limitations of Builtins): Document it.
* tests/m4sh.at (ECHO_C): New test.
* THANKS: Update.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>

ChangeLog

@@ -1,3 +1,14 @@
+2009-06-30  Jan Madzik  <jmadzik@gmail.com>  (tiny change)
+	    Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
+
+	Avoid AIX 6.1 ksh88 ECHO_C command substitution bug.
+	* lib/m4sugar/m4sh.m4 (_AS_ECHO_N_PREPARE): Ensure more than
+	one character is output with `\c'; reset echo output state
+	if buggy ksh was detected, and set ECHO_T instead of ECHO_C.
+	* doc/autoconf.texi (Limitations of Builtins): Document it.
+	* tests/m4sh.at (ECHO_C): New test.
+	* THANKS: Update.
+
 2009-06-27  William Pursell  <bill.pursell@gmail.com>  (tiny change)
 
 	Fix grammaro in documenation.

THANKS

@@ -160,6 +160,7 @@ Iohannes m zmoelnig         zmoelnig@iem.at
 J C Fitzgerald              v7022@wave.co.nz
 Jaap Haitsma                jaap@haitsma.org
 James A. Lupo               lupoja@feynman.ml.wpafb.af.mil
+Jan Madzik                  jmadzik@gmail.com
 Jason Molenda               jsm@cygnus.com
 Jeff Garzik                 jgarzik@pobox.com
 Jeff Painter                ?

doc/autoconf.texi

@@ -15733,7 +15733,10 @@ their handling.  For @samp{echo '\n' | wc -l}, the @command{sh} of
 Solaris outputs 2, but Bash and Zsh (in @command{sh} emulation mode) output 1.
 The problem is truly @command{echo}: all the shells
 understand @samp{'\n'} as the string composed of a backslash and an
-@samp{n}.
+@samp{n}.  Within a command substitution, @samp{echo 'string\c'} will
+mess up the internal state of ksh88 on AIX 6.1 so that it will print
+the first character @samp{s} only, followed by a newline, and then
+entirely drop the output of the next echo in a command substitution.
 
 Because of these problems, do not pass a string containing arbitrary
 characters to @command{echo}.  For example, @samp{echo "$foo"} is safe

lib/m4sugar/m4sh.m4

@@ -780,14 +780,19 @@ m4_defun_init([_AS_ECHO_LOG],
 # display the checking message.  In addition, caching something used once
 # has little interest.
 # Idea borrowed from dist 3.0.  Use `*c*,', not `*c,' because if `\c'
-# failed there is also a newline to match.
+# failed there is also a newline to match.  Use `xy' because `\c' echoed
+# in a command substitution prints only the first character of the output
+# with ksh version M-11/16/88f on AIX 6.1; it needs to be reset by another
+# backquoted echo.
 m4_defun([_AS_ECHO_N_PREPARE],
 [ECHO_C= ECHO_N= ECHO_T=
-case `echo -n x` in @%:@((((
+case `echo -n x` in @%:@(((((
 -n*)
-  case `echo 'x\c'` in
+  case `echo 'xy\c'` in
   *c*) ECHO_T='	';;	# ECHO_T is single tab character.
-  *)   ECHO_C='\c';;
+  xy)  ECHO_C='\c';;
+  *)   echo `echo ksh88 bug on AIX 6.1` > /dev/null
+       ECHO_T='	';;
   esac;;
 *)
   ECHO_N='-n';;

tests/m4sh.at

@@ -1412,3 +1412,23 @@ AT_CHECK_M4SH
 AT_CHECK([./script])
 
 AT_CLEANUP
+
+
+## -------- ##
+## ECHO_C.  ##
+## -------- ##
+
+AT_SETUP([ECHO_C])
+
+AT_DATA_M4SH([script.as], [[dnl
+AS_INIT
+_AS_PREPARE
+foo=`echo foobar`
+echo "$foo"
+]])
+
+AT_CHECK_M4SH
+AT_CHECK([./script], [], [foobar
+])
+
+AT_CLEANUP