busybox/shell
Denys Vlasenko 66c5b12dbf ash: fix TMOUT not restoring tty attributes
function                                             old     new   delta
pgetc                                                420     500     +80
readtoken1                                          3202    3239     +37
read_line_input                                     3316    3337     +21
udhcpc_main                                         2610    2630     +20
file_get                                             266     272      +6
expandarg                                            958     963      +5
localcmd                                             257     259      +2
addLines                                              85      87      +2
read_line                                             94      95      +1
ed_main                                             2540    2541      +1
timed_out                                              1       -      -1
lineedit_read_key                                    256     255      -1
alrm_sighandler                                       44       -     -44
cmdloop                                              539     434    -105
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 10/2 up/down: 175/-151)          Total: 24 bytes
   text    data     bss     dec     hex filename
 887379     936   17200  905515   dd12b busybox_old
 887411     936   17192  905539   dd143 busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2011-02-08 05:07:02 +01:00
..
ash_test echo: do not retry on write errors 2011-02-07 02:03:51 +01:00
hush_test echo: do not retry on write errors 2011-02-07 02:03:51 +01:00
msh_test whitespace fixes 2010-01-25 13:39:24 +01:00
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: fix TMOUT not restoring tty attributes 2011-02-08 05:07:02 +01:00
brace.txt hush: wait for cmd to complete, and immediately store its exitcode in $? 2009-11-15 19:58:19 +01:00
Config.src hush: use FEATURE_SH_NOFORK to enable NOFORK trick 2011-02-02 18:38:57 +01:00
cttyhack.c mass removal of underscores from _BB_DIR_foo and _BB_SUID_foo 2011-01-18 13:58:01 +01:00
hush_doc.txt
hush_leaktool.sh
hush.c ash: fix TMOUT not restoring tty attributes 2011-02-08 05:07:02 +01:00
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 shell/math: better comment. no code changes 2010-09-17 18:02:17 +02:00
math.h shell/math: deconvolute and explain ?: handling. Give better error message 2010-09-16 11:50:46 +02:00
random.c *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
random.h *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
README update shell/README 2010-05-20 12:56:14 +02:00
README.job
shell_common.c whitespace fixes 2011-02-03 00:05:48 +01:00
shell_common.h *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +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.