busybox/shell
Johannes Schindelin 9d4dc84a76 ash: protect WIFSTOPPED use with #if JOBS
This change fixes the build in setups where there are
no headers defining WIFSTOPPED and WSTOPSIG (where JOBS has to be
set to 0).

This partially reverts 4700fb5be (ash: make dowait() a bit more
readable. Logic is unchanged, 2015-10-09).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-07-15 11:38:00 +02:00
..
ash_test hush: fix "(sleep 1; exit 3) & sleep 2; echo $?; wait $!; echo $?" 2017-07-07 22:56:02 +02:00
hush_test hush: add support for "set -e" 2017-07-14 13:36:48 +02:00
ash_doc.txt
ash_ptr_hack.c
ash.c ash: protect WIFSTOPPED use with #if JOBS 2017-07-15 11:38:00 +02:00
brace.txt
Config.src wget: add a big explanation what TLS code implements and what does not 2017-01-30 16:27:37 +01:00
cttyhack.c
hush_doc.txt
hush_leaktool.sh
hush.c hush: make "wait %1" work even if the job is dead 2017-07-14 19:58:46 +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
match.h
math.c
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
random.h
README
README.job
shell_common.c fixes for bugs found by make_single_applets.sh 2017-07-03 21:31:16 +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.