busybox/shell
Denys Vlasenko 579ad107a6 ash: [EXPAND] Removed herefd hack
Upstream commit:

    Date: Sun, 11 Nov 2007 15:00:06 +0800
    [EXPAND] Removed herefd hack

    The herefd hack goes back more than a decade.  it limits the amount of
    memory we have to allocate when expanding here-documents by writing the
    result out from time to time.  However, it's no longer safe because the
    stack is used to place intermediate results too and there we certainly
    don't want to write them out should we be short on memory.

    In any case, with today's computers we can afford to keep the entire
    result in memory and write them out at the end.

function                                             old     new   delta
redirect                                            1268    1264      -4
ash_main                                            1485    1478      -7
subevalvar                                          1157    1132     -25
growstackstr                                          54      24     -30
argstr                                              1192    1154     -38
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/5 up/down: 0/-104)           Total: -104 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2016-10-25 21:10:20 +02:00
..
ash_test ash testsuite: fix false positives 2016-10-07 04:07:05 +02:00
hush_test sh testsuite: add tests for exitcode on failure to exec 2016-10-03 00:55:34 +02:00
ash_doc.txt ash: fix TRACE commands 2009-03-19 23:09:58 +00:00
ash_ptr_hack.c *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
ash.c ash: [EXPAND] Removed herefd hack 2016-10-25 21:10:20 +02:00
brace.txt hush: wait for cmd to complete, and immediately store its exitcode in $? 2009-11-15 19:58:19 +01:00
Config.src config: disentangle PREFER_APPLETS from SH_STANDALONE and SH_NOFORK 2016-07-22 18:48:38 +02:00
cttyhack.c cttyhack: handle multiple consoles found in sysfs 2012-02-04 21:55:01 +01:00
hush_doc.txt hush: implement break and continue 2008-07-28 23:04:34 +00:00
hush_leaktool.sh hush: fix "export not_yet_defined_var", fix parsing of "cmd | }" 2009-04-19 23:07:51 +00:00
hush.c ash,hush: set exit code 127 in "sh /does/not/exist" case 2016-10-25 17:00:13 +02:00
Kbuild.src *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
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 move endofname() to libbb 2013-02-26 00:36:53 +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 update shell/README 2010-05-20 12:56:14 +02:00
README.job
shell_common.c ash: [VAR] Initialise OPTIND after importing environment 2016-09-30 14:46:41 +02:00
shell_common.h ash: [VAR] Initialise OPTIND after importing environment 2016-09-30 14:46:41 +02:00

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.