busybox/shell
Ron Yorston 549deab5ab ash: move parse-time quote flag detection to run-time
Because the parser does not recursively parse parameter expansion
with respect to quotes, we can't accurately determine quote status at
parse time.  This patch works around this by moving the quote detection
to run-time where we do interpret it recursively.

Test case:
   foo=\\ echo "<${foo#[\\]}>"
Old result:
   <\>
New result:
   <>

Do not quote back slashes in parameter expansions outside quotes.

Test case:
   a=/b/c/*
   b=\\
   echo ${a%$b*}
Old result:
   /b/c/*
New result:
   /b/c/

Based on commits 880d952, 7cfd8be, 0d7d660 and a7c21a6 from
git://git.kernel.org/pub/scm/utils/dash/dash.git by Herbert Xu

function                                             old     new   delta
argstr                                              1164    1193     +29
memtodest                                            147     174     +27
subevalvar                                          1153    1177     +24
redirect                                            1279    1282      +3
dolatstr                                               5       7      +2
static.spclchars                                      10       9      -1
expandarg                                            962     960      -2
evalcase                                             273     271      -2
evalcommand                                         1204    1197      -7
rmescapes                                            236     227      -9
preglob                                               27       8     -19
evalvar                                              604     582     -22
cmdputs                                              389     334     -55
readtoken1                                          3163    3061    -102
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 5/9 up/down: 85/-219)          Total: -134 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2015-05-18 09:57:51 +02:00
..
ash_test ash: move parse-time quote flag detection to run-time 2015-05-18 09:57:51 +02:00
hush_test hush: document buggy handling of duplicate "local" 2015-04-18 19:38:13 +02:00
msh_test
ash_doc.txt
ash_ptr_hack.c
ash.c ash: move parse-time quote flag detection to run-time 2015-05-18 09:57:51 +02:00
brace.txt
Config.src ash,hush: optional support for $HISTFILESIZE. 2011-03-31 13:16:52 +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 libbb: introduce and use is_prefixed_with() 2015-03-12 17:48:34 +01:00
Kbuild.src
match.c
match.h
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 typo fix in comment 2013-07-14 01:23:06 +02:00
shell_common.h *: declare strings with ALIGN1, as appropriate 2012-07-24 15:56:37 +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.