busybox

History

Denys Vlasenko eaf9436b08 ash: [REDIR] Move null redirect checks into caller Upstream commit: Date: Thu, 27 May 2010 14:21:17 +0800 [REDIR] Move null redirect checks into caller The null redirect checks were added as an optimisation to avoid unnecessary memory allocations. However, we could avoid this completely by simply making the caller avoid making a redirection unless it is not null. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> function old new delta evaltree 784 809 +25 evalcommand 1251 1261 +10 hashvar 59 62 +3 dotcmd 321 319 -2 clearredir 37 30 -7 popredir 183 162 -21 redirect 1264 1233 -31 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 4/4 up/down: 63/-61) Total: -23 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>		2016-10-25 21:46:03 +02:00
..
ash_test	ash testsuite: fix false positives	2016-10-07 04:07:05 +02:00
hush_test	sh testsuite: add tests for exitcode on failure to exec	2016-10-03 00:55:34 +02:00
ash_doc.txt
ash_ptr_hack.c	*: make GNU licensing statement forms more regular	2010-08-16 20:14:46 +02:00
ash.c	ash: [REDIR] Move null redirect checks into caller	2016-10-25 21:46:03 +02:00
brace.txt
Config.src	config: disentangle PREFER_APPLETS from SH_STANDALONE and SH_NOFORK	2016-07-22 18:48:38 +02:00
cttyhack.c	cttyhack: handle multiple consoles found in sysfs	2012-02-04 21:55:01 +01:00
hush_doc.txt
hush_leaktool.sh
hush.c	ash,hush: set exit code 127 in "sh /does/not/exist" case	2016-10-25 17:00:13 +02:00
Kbuild.src	*: make GNU licensing statement forms more regular	2010-08-16 20:14:46 +02:00
match.c	shell/match.c: shrink by dropping double bool inversion	2010-09-12 15:06:42 +02:00
match.h	hush: optimize #[#] and %[%] for speed. size -2 bytes.	2010-09-04 21:21:07 +02:00
math.c	typo fix in comment	2014-11-20 01:43:30 +01:00
math.h	move endofname() to libbb	2013-02-26 00:36:53 +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	ash: [VAR] Initialise OPTIND after importing environment	2016-09-30 14:46:41 +02:00
shell_common.h	ash: [VAR] Initialise OPTIND after importing environment	2016-09-30 14:46:41 +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.