busybox/shell
Denys Vlasenko b437df1157 inetd: suppress aliasing warning
function                                             old     new   delta
sigprocmask2                                           -       8      +8
wait_for_child_or_signal                             213     218      +5
dowait                                               424     429      +5
block_CHLD_HUP_ALRM                                   62      59      -3
sigprocmask_SIG_SETMASK                               16       -     -16
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 2/1 up/down: 18/-19)             Total: -1 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2018-12-08 15:35:24 +01:00
..
ash_test ash: expand: Do not quote backslashes in unquoted parameter expansion 2018-08-07 18:58:02 +02:00
hush_test ash: expand: Do not quote backslashes in unquoted parameter expansion 2018-08-07 18:58:02 +02:00
ash_doc.txt
ash_ptr_hack.c
ash.c inetd: suppress aliasing warning 2018-12-08 15:35:24 +01:00
brace.txt
Config.src hush: allow hush to run embedded scripts 2018-11-27 16:13:07 +01:00
cttyhack.c regularize format of source file headers, no code changes 2017-09-18 16:28:43 +02:00
hush_doc.txt
hush_leaktool.sh
hush.c inetd: suppress aliasing warning 2018-12-08 15:35:24 +01:00
Kbuild.src
match.c hush: fix a='a\\'; echo "${a%\\\\}" 2018-03-02 20:48:36 +01:00
match.h
math.c shell: handle $((NUM++...) like bash does. Closes 10706 2018-01-28 20:13:33 +01:00
math.h
random.c whitespace fixes 2018-07-17 15:04:17 +02:00
random.h
README
README.job
shell_common.c ash,hush: fold shell_builtin_read() way-too-many params into a struct param 2018-08-05 18:11:15 +02:00
shell_common.h ash,hush: fold shell_builtin_read() way-too-many params into a struct param 2018-08-05 18:11:15 +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.