busybox/shell
Denys Vlasenko f977e004ce ash: eval: Only restore exit status on exit/return
Upstream commit:

    Date: Fri, 14 Dec 2018 13:52:02 +0800
    eval: Only restore exit status on exit/return

    We unconditionally restore the saved status in exitreset, which
    is incorrect as we only want to do it for exitcmd and returncmd.
    This patch fixes the problem by introducing EXEND.

    Reported-by: Martijn Dekker <martijn@inlv.org>
    Fixes: da30b4b78769 ("[BUILTIN] Exit without arguments in a trap...")
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2020-02-20 16:54:29 +01:00
..
ash_test hush: implement "return NUM in trap sets $? after trap" 2020-02-20 16:37:59 +01:00
hush_test hush: implement "return NUM in trap sets $? after trap" 2020-02-20 16:37:59 +01:00
ash_doc.txt
ash_ptr_hack.c
ash.c ash: eval: Only restore exit status on exit/return 2020-02-20 16:54:29 +01:00
brace.txt
Config.src shell: implement optional "BASE#nnnn" numeric literals 2019-05-19 17:23:31 +02:00
cttyhack.c config: update size information 2018-12-28 03:20:17 +01:00
hush_doc.txt
hush_leaktool.sh
hush.c hush: implement "return NUM in trap sets $? after trap" 2020-02-20 16:37:59 +01:00
Kbuild.src Make it possible to select "sh" and "bash" aliases without selecting ash or hush 2016-12-23 16:56:43 +01:00
match.c hush: fix a='a\\'; echo "${a%\\\\}" 2018-03-02 20:48:36 +01:00
match.h
math.c shell: better comments in BASE#nn code 2019-10-22 14:25:43 +02:00
math.h shell: move all definitions of strto_arith_t() together 2019-05-26 14:02:10 +02:00
random.c whitespace fixes 2018-07-17 15:04:17 +02:00
random.h
README
README.job
shell_common.c shell/ulimit: code shrink 2019-10-21 16:47:09 +02:00
shell_common.h hush: fix "export PS1=xyz" and "local PS1=xyz" messing up prompt 2019-05-14 18:56:04 +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.