busybox/shell
Denys Vlasenko d70e0e995e *: add INSERTs to *.src files where appropriate
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2010-06-08 12:15:11 +02:00
..
ash_test ash: fix redirection of fd 0 in scripts are sourced from interactive ash 2010-06-03 04:28:28 +02:00
hush_test hush: fix segfault in ${?:N:M} 2010-05-22 06:20:26 +02:00
msh_test whitespace fixes 2010-01-25 13:39:24 +01:00
ash_doc.txt ash: fix TRACE commands 2009-03-19 23:09:58 +00:00
ash_ptr_hack.c
ash.c fix a few goofs uncovered by "make allnoconfig" testing 2010-06-06 05:07:11 +02:00
bbsh.c *: remove some uses of argc 2010-01-04 14:15:38 +01:00
brace.txt hush: wait for cmd to complete, and immediately store its exitcode in $? 2009-11-15 19:58:19 +01:00
Config.src *: add INSERTs to *.src files where appropriate 2010-06-08 12:15:11 +02:00
cttyhack.c cttyhack: don't do anything if ctty is already available 2010-05-14 04:08:20 +02:00
hush_doc.txt hush: implement break and continue 2008-07-28 23:04:34 +00:00
hush_leaktool.sh hush: fix "export not_yet_defined_var", fix parsing of "cmd | }" 2009-04-19 23:07:51 +00:00
hush.c bbconfig: make it independent from printf functions 2010-06-07 14:14:26 +02:00
Kbuild.src *: add INSERTs to *.src files where appropriate 2010-06-08 12:15:11 +02:00
match.c shell: split read builtin from ash 2010-01-12 22:11:24 +01:00
match.h hush: use ash's read builtin 2010-01-12 23:29:57 +01:00
math.c hush: use ash's read builtin 2010-01-12 23:29:57 +01:00
math.h hush: use ash's read builtin 2010-01-12 23:29:57 +01:00
random.c ash,hush: fix $RANDOM in children being repeated 2009-10-12 15:25:01 +02:00
random.h shell: split read builtin from ash 2010-01-12 22:11:24 +01:00
README update shell/README 2010-05-20 12:56:14 +02:00
README.job
shell_common.c shell: consolidate builtin_foo.? into shell_common.?; delete obsolete shells 2010-05-23 17:49:50 +02:00
shell_common.h shell: consolidate builtin_foo.? into shell_common.?; delete obsolete shells 2010-05-23 17:49:50 +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.