busybox/shell
Denys Vlasenko ecc85832f8 ash: expand: Merge syntax/quotes in memtodest with flags
Upstream commit:

    Date: Mon, 28 May 2018 00:17:39 +0800
    expand: Merge syntax/quotes in memtodest with flags

    The function arguments syntax and quotes are both derived from
    the expansion flags.  As syntax is only used by memtodest we do
    not need to maintain it outside of the function at all.

    The only place that uses something other than BASESYNTAX or DQSYNTAX
    is exptilde.  However in that case DQSYNTAX has exactly the same
    effect as SQSYNTAX.

    This patch merges these two arguments into a single flags.  The
    macro QUOTES_KEEPNUL has been renamed to EXP_KEEPNUL in order
    to keep the namespace separate.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2020-02-20 10:37:30 +01:00
..
ash_test ash: eval: Fail immediately with redirections errors for simple command 2020-02-20 09:36:51 +01:00
hush_test ash,hush: testcase for "exit" without arguments in a trap 2020-02-19 12:10:41 +01:00
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: expand: Merge syntax/quotes in memtodest with flags 2020-02-20 10:37:30 +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: add comment about masked SIGCHLD, handle SIG_IGNed SIGHUP as in bash 2020-02-18 16:46:01 +01:00
Kbuild.src Make it possible to select "sh" and "bash" aliases without selecting ash or hush 2016-12-23 16:56:43 +01:00
match.c hush: fix a='a\\'; echo "${a%\\\\}" 2018-03-02 20:48:36 +01:00
match.h hush: optimize #[#] and %[%] for speed. size -2 bytes. 2010-09-04 21:21:07 +02:00
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 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 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

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.