busybox/shell
Kylie McClain 40eea690c7 Fix compiling with musl's utmp stubs
This patch fixes compiling busybox with FEATURE_UTMP and _WTMP enabled.
musl, while not really support utmp/wtmp, provides stub functions, as well
as variables such as _PATH_UTMP, so that programs using utmp or wtmp can
still compile fine.

My reasoning for this patch is that on Exherbo, I'm currently trying to get
us to be able to use the same busybox config file for both glibc and musl
systems, using utmp/wtmp on systems that support it, and using the stubs
on musl without needing two different configs.

As of latest musl git, it provides all utmp functions needed; 1.1.12 doesn't,
but I sent a patch to Rich to add the utmp{,x}name functions expected to
exist, which was merged into musl upstream.

Signed-off-by: Kylie McClain <somasissounds@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2016-02-01 01:36:05 +01:00
..
ash_test ash: add support for bash 'function' keyword 2015-11-04 19:30:24 +01:00
hush_test hush-misc/func_args1.tests: remove "UNFIXED BUG", it does not fail 2015-11-04 14:50:19 +01:00
msh_test
ash_doc.txt
ash_ptr_hack.c *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
ash.c Fix compiling with musl's utmp stubs 2016-02-01 01:36:05 +01:00
brace.txt
Config.src ash,hush: optional support for $HISTFILESIZE. 2011-03-31 13:16:52 +02:00
cttyhack.c cttyhack: handle multiple consoles found in sysfs 2012-02-04 21:55:01 +01:00
hush_doc.txt
hush_leaktool.sh
hush.c hush: code shrink 2015-10-11 21:47:11 +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
README.job
shell_common.c build system: -fno-builtin-printf 2015-10-07 22:42:45 +02:00
shell_common.h *: declare strings with ALIGN1, as appropriate 2012-07-24 15:56:37 +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.