busybox

History

Ron Yorston 943e81f5db ash: only catch unexpected exceptions in PS1 expansion Commit `d1a2fa2a4` (ash: catch error in arithmetic expansion in PS1) catches all exceptions raised by expandarg(). Some exceptions, such as the EXEXIT raised when command expansion is used, are expected: export PS1='$(echo "$ ")' These should be processed normally or the shell hangs at the prompt. function old new delta expandstr 344 353 +9 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 1/0 up/down: 9/0) Total: 9 bytes Signed-off-by: Ron Yorston <rmy@pobox.com> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>		2019-07-31 13:44:32 +02:00
..
ash_test	hush: remove test for "echo ${-}" errorring out - now it works	2019-05-19 16:35:56 +02:00
hush_test	hush: remove test for "echo ${-}" errorring out - now it works	2019-05-19 16:35:56 +02:00
ash_doc.txt
ash_ptr_hack.c
ash.c	ash: only catch unexpected exceptions in PS1 expansion	2019-07-31 13:44:32 +02:00
brace.txt
Config.src	shell: implement optional "BASE#nnnn" numeric literals	2019-05-19 17:23:31 +02:00
cttyhack.c	config: update size information	2018-12-28 03:20:17 +01:00
hush_doc.txt
hush_leaktool.sh
hush.c	libbb: reduce the overhead of single parameter bb_error_msg() calls	2019-07-02 11:35:03 +02:00
Kbuild.src
match.c	hush: fix a='a\\'; echo "${a%\\\\}"	2018-03-02 20:48:36 +01:00
match.h
math.c	shell: move all definitions of strto_arith_t() together	2019-05-26 14:02:10 +02:00
math.h	shell: move all definitions of strto_arith_t() together	2019-05-26 14:02:10 +02:00
random.c	whitespace fixes	2018-07-17 15:04:17 +02:00
random.h
README
README.job
shell_common.c	libbb: reduce the overhead of single parameter bb_error_msg() calls	2019-07-02 11:35:03 +02:00
shell_common.h	hush: fix "export PS1=xyz" and "local PS1=xyz" messing up prompt	2019-05-14 18:56:04 +02:00

README

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.