busybox/shell
Denys Vlasenko 9fed83a7cc hush: fix false positive in unset.tests
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-08-29 14:35:58 +02:00
..
ash_test hush: fix "getopts" builtin to not be upset by other builtins calling getopt() 2017-08-29 13:38:30 +02:00
hush_test hush: fix false positive in unset.tests 2017-08-29 14:35:58 +02:00
ash_doc.txt
ash_LINENO.patch ash: stage backported LINENO support as a separate patch 2017-08-17 16:43:33 +02:00
ash_ptr_hack.c
ash.c ash: more s/error/perror/ for better error reporting 2017-08-23 14:52:56 +02:00
brace.txt
Config.src config: deindent all help texts 2017-07-21 09:50:55 +02:00
cttyhack.c make 17 state-changing execing applets (ex: "nice PROG ARGS") noexec 2017-08-04 19:55:01 +02:00
hush_doc.txt
hush_leaktool.sh
hush.c hush: GETOPT_RESET() _after_ getopts too. 2017-08-29 14:32:17 +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 do not use `a' quoting style in comments 2017-08-02 14:26:33 +02:00
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 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 hush: GETOPT_RESET() _after_ getopts too. 2017-08-29 14:32:17 +02:00
shell_common.h shell: more efficient check for EOL in read 2017-08-09 14:04:07 +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.