busybox/shell
Ron Yorston 71df2d3589 hush: allow hush to run embedded scripts
Embedded scripts require a shell to be present in the BusyBox
binary.  Allow either ash or hush to be used for this purpose.
If both are enabled ash takes precedence.

The size of the binary is unchanged in the default configuration:
both ash and hush are present but support for embedded scripts
isn't compiled into hush.

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2018-11-27 16:13:07 +01:00
..
ash_test ash: expand: Do not quote backslashes in unquoted parameter expansion 2018-08-07 18:58:02 +02:00
hush_test ash: expand: Do not quote backslashes in unquoted parameter expansion 2018-08-07 18:58:02 +02:00
ash_doc.txt
ash_ptr_hack.c
ash.c hush: allow hush to run embedded scripts 2018-11-27 16:13:07 +01:00
brace.txt
Config.src hush: allow hush to run embedded scripts 2018-11-27 16:13:07 +01:00
cttyhack.c
hush_doc.txt
hush_leaktool.sh
hush.c hush: allow hush to run embedded scripts 2018-11-27 16:13:07 +01:00
Kbuild.src
match.c
match.h
math.c
math.h
random.c whitespace fixes 2018-07-17 15:04:17 +02:00
random.h
README
README.job
shell_common.c ash,hush: fold shell_builtin_read() way-too-many params into a struct param 2018-08-05 18:11:15 +02:00
shell_common.h ash,hush: fold shell_builtin_read() way-too-many params into a struct param 2018-08-05 18:11:15 +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.