busybox

History

Denys Vlasenko 061a09091f ash: [BUILTIN] Use EXEXIT in place of EXEXEC Upstream commit: Date: Sun, 28 Nov 2010 20:44:37 +0800 [BUILTIN] Use EXEXIT in place of EXEXEC The intended semantics of EXEXEC are identical to EXEXIT, so simplify by using EXEXIT directly. Functional change: in edge cases (exec within a trap handler), this causes the exit status from exec not to be clobbered. For example, without this patch: $ sh -c 'trap "exec nonexistent" EXIT'; echo $? exec: 1: nonexistent: not found 0 And with it: $ sh -c 'trap "exec nonexistent" EXIT'; echo $? exec: 1: nonexistent: not found 127 Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>		2016-10-25 17:24:25 +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
ash.c	ash: [BUILTIN] Use EXEXIT in place of EXEXEC	2016-10-25 17:24:25 +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
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
match.c
match.h
math.c	typo fix in comment	2014-11-20 01:43:30 +01:00
math.h
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.