busybox/shell
Denys Vlasenko 25ce3ee9f3 typo fix in comment
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2013-07-14 01:23:06 +02:00
..
ash_test ash: fix a bug in >${varexp} handling. Closes 5282 2012-06-09 02:06:57 +02:00
hush_test hush: fix for "while false && true; do echo BUG; break; done". closes 6170 2013-04-07 18:16:58 +02:00
msh_test
ash_doc.txt
ash_ptr_hack.c
ash.c unicode: check $LC_CTYPE too to detect Unicode mode 2013-07-05 22:00:57 +02:00
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 typo fix in comment 2013-07-08 03:13:08 +02:00
Kbuild.src
match.c shell/match.c: shrink by dropping double bool inversion 2010-09-12 15:06:42 +02:00
match.h
math.c move endofname() to libbb 2013-02-26 00:36:53 +01:00
math.h move endofname() to libbb 2013-02-26 00:36:53 +01:00
random.c
random.h
README
README.job
shell_common.c typo fix in comment 2013-07-14 01:23:06 +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.