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Denys Vlasenko 469998015f ash: [PARSER] Add FAKEEOFMARK for expandstr 
Upstream commit:

    Date: Thu, 27 Dec 2007 13:54:16 +1100
    [PARSER] Add FAKEEOFMARK for expandstr

    Previously expandstr used the string "" to indicate that it needs to be
    treated just like a here-doc except that there is no terminator.  However,
    the string "" is in fact a valid here-doc terminator so now that we deal
    with it correctly expandstr no longer works in the presence of new-lines
    in the prompt.

    This patch introduces the FAKEEOFMARK macro which does not equal any
    real EOF marker but is distinct from the NULL pointer which is used to
    indicate non-here-doc contexts.

    Thanks to Markus Triska for reporting this regression.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Unfortunately, I did not find the failing example for this old fix.

I also tweaked the code which was added by this commit:
"
Date: Mon Sep 24 18:30:02 2007 +0000
ash: fix prompt expansion (Natanael Copa <natanael.copa@gmail.com>)
"
since other parts of code do expect expandstr() to use DQSYNTAX, not PSSYNTAX.

function                                             old     new   delta
parse_stream                                        2609    2634     +25
setprompt_if                                         128     133      +5
read_profile                                          32      37      +5
evalcommand                                         1334    1339      +5
expandstr                                            122     120      -2
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/1 up/down: 40/-2)              Total: 38 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-07-29 21:12:29 +02:00
..
ash_test hush: fix handling of empty heredoc EOF marker 2017-07-29 20:43:26 +02:00
hush_test hush: fix handling of empty heredoc EOF marker 2017-07-29 20:43:26 +02:00
ash_doc.txt
ash_ptr_hack.c *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
ash.c ash: [PARSER] Add FAKEEOFMARK for expandstr 2017-07-29 21:12:29 +02:00
brace.txt
Config.src config: deindent all help texts 2017-07-21 09:50:55 +02:00
cttyhack.c config: deindent all help texts 2017-07-21 09:50:55 +02:00
hush_doc.txt
hush_leaktool.sh
hush.c hush: fix handling of empty heredoc EOF marker 2017-07-29 20:43:26 +02:00
Kbuild.src Make it possible to select "sh" and "bash" aliases without selecting ash or hush 2016-12-23 16:56:43 +01:00
match.c shell/match.c: shrink by dropping double bool inversion 2010-09-12 15:06:42 +02:00
match.h hush: optimize #[#] and %[%] for speed. size -2 bytes. 2010-09-04 21:21:07 +02:00
math.c typo fix in comment 2014-11-20 01:43:30 +01:00
math.h Make it possible to select "sh" and "bash" aliases without selecting ash or hush 2016-12-23 16:56:43 +01:00
random.c ash,hush: fix a thinko about 2^64-1 factorization 2014-03-15 09:25:46 +01:00
random.h ash,hush: improve randomness of $RANDOM, add easy-ish way to test it 2014-03-13 12:52:43 +01:00
README
README.job
shell_common.c shell: optional support for read -t N.NNN, closes 10101 2017-07-20 16:09:31 +02:00
shell_common.h ash: [VAR] Initialise OPTIND after importing environment 2016-09-30 14:46:41 +02:00

README 

http://www.opengroup.org/onlinepubs/9699919799/
Open Group Base Specifications Issue 7


http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html
Shell & Utilities

It says that any of the standard utilities may be implemented
as a regular shell built-in. It gives a list of utilities which
are usually implemented that way (and some of them can only
be implemented as built-ins, like "alias"):

alias
bg
cd
command
false
fc
fg
getopts
jobs
kill
newgrp
pwd
read
true
umask
unalias
wait


http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
Shell Command Language

It says that shell must implement special built-ins. Special built-ins
differ from regular ones by the fact that variable assignments
done on special builtin are *PRESERVED*. That is,

VAR=VAL special_builtin; echo $VAR

should print VAL.

(Another distinction is that an error in special built-in should
abort the shell, but this is not such a critical difference,
and moreover, at least bash's "set" does not follow this rule,
which is even codified in autoconf configure logic now...)

List of special builtins:

. file
: [argument...]
break [n]
continue [n]
eval [argument...]
exec [command [argument...]]
exit [n]
export name[=word]...
export -p
readonly name[=word]...
readonly -p
return [n]
set [-abCefhmnuvx] [-o option] [argument...]
set [+abCefhmnuvx] [+o option] [argument...]
set -- [argument...]
set -o
set +o
shift [n]
times
trap n [condition...]
trap [action condition...]
unset [-fv] name...

In practice, no one uses this obscure feature - none of these builtins
gives any special reasons to play such dirty tricks.

However. This section also says that *function invocation* should act
similar to special built-in. That is, variable assignments
done on function invocation should be preserved after function invocation.

This is significant: it is not unthinkable to want to run a function
with some variables set to special values. But because of the above,
it does not work: variable will "leak" out of the function.