busybox

History

Denys Vlasenko b0d2dc7d62 ash: exec: Do not allocate stack string in padvance Upstream commit: Date: Sat, 19 May 2018 02:39:48 +0800 exec: Do not allocate stack string in padvance Many callers of padvance immediately free the allocated string so this patch moves the stalloc call to the caller. Instead of returning the allocated string, padvance now returns the length to allocate (this may be longer than the actual string length, even including the NUL). For the case where we would previously return NULL, we now return -1. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>		2020-02-17 15:59:44 +01:00
..
ash_test	ash: expand: Fix trailing newlines processing in backquote expanding	2020-02-17 10:24:32 +01:00
hush_test	ash: expand: Fix trailing newlines processing in backquote expanding	2020-02-17 10:24:32 +01:00
ash_doc.txt
ash_ptr_hack.c
ash.c	ash: exec: Do not allocate stack string in padvance	2020-02-17 15:59:44 +01:00
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	ash,hush: allow builtins to be tab-completed, closes 7532	2020-01-29 15:23:17 +01:00
Kbuild.src
match.c	hush: fix a='a\\'; echo "${a%\\\\}"	2018-03-02 20:48:36 +01:00
match.h
math.c	shell: better comments in BASE#nn code	2019-10-22 14:25:43 +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	shell/ulimit: code shrink	2019-10-21 16:47:09 +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.