busybox/shell
Denys Vlasenko 7ce209b9d4 shell_builtin_read: set cc[VMIN] to 1; lineedit: don't clear c_cc[VINTR]
First change fixes "read -n NUM". Apparently poll() won't report
data availability if cc[VMIN] > 1 until there are at least cc[VMIN] bytes.

function                                             old     new   delta
read_line_input                                     3885    3877      -8
shell_builtin_read                                  1097    1087     -10
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-18)             Total: -18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2012-01-15 22:58:06 +01:00
..
ash_test slightly better wording in comments 2011-02-21 03:47:50 +01:00
hush_test hush: fix remaining known two bugs with IFS expansion. Closes 4027. 2011-08-01 18:16:43 +02:00
msh_test whitespace fixes 2010-01-25 13:39:24 +01:00
ash_doc.txt ash: fix TRACE commands 2009-03-19 23:09:58 +00:00
ash_ptr_hack.c *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
ash.c ash: in standalone mode, search in $PATH if /proc/self/exe doesn't exist 2011-12-20 06:10:35 +01:00
brace.txt hush: wait for cmd to complete, and immediately store its exitcode in $? 2009-11-15 19:58:19 +01:00
Config.src ash,hush: optional support for $HISTFILESIZE. 2011-03-31 13:16:52 +02:00
cttyhack.c cttyhack: move /sys/class/tty/console/active check to the front 2011-10-31 16:57:04 +01:00
hush_doc.txt hush: implement break and continue 2008-07-28 23:04:34 +00:00
hush_leaktool.sh hush: fix "export not_yet_defined_var", fix parsing of "cmd | }" 2009-04-19 23:07:51 +00:00
hush.c lineedit: remove SAVE_HISTORY bit, ->hist_file can be used as indicator 2011-09-04 16:15:24 +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 shell/math: better comment. no code changes 2010-09-17 18:02:17 +02:00
math.h shell/math: deconvolute and explain ?: handling. Give better error message 2010-09-16 11:50:46 +02:00
random.c *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
random.h *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +02:00
README update shell/README 2010-05-20 12:56:14 +02:00
README.job hush: small code shrink; style fixes 2007-04-20 08:35:45 +00:00
shell_common.c shell_builtin_read: set cc[VMIN] to 1; lineedit: don't clear c_cc[VINTR] 2012-01-15 22:58:06 +01:00
shell_common.h *: make GNU licensing statement forms more regular 2010-08-16 20:14:46 +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.