busybox

History

Ron Yorston a81700bc08 hush: add bash-compatible EPOCH variables Bash 5.0 added the dynamic variable EPOCHSECONDS and EPOCHREALTIME which return the number of seconds since the Unix Epoch as an integer or float. These are useful for logging or tracing. function old new delta get_local_var_value 207 302 +95 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 1/0 up/down: 95/0) Total: 95 bytes text data bss dec hex filename 938702 4203 1888 944793 e6a99 busybox_old 938797 4203 1888 944888 e6af8 busybox_unstripped Signed-off-by: Ron Yorston <rmy@pobox.com> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>		2019-04-16 18:29:52 +02:00
..
ash_test	ash: expand: Do not quote backslashes in unquoted parameter expansion	2018-08-07 18:58:02 +02:00
hush_test	ash: expand: Do not quote backslashes in unquoted parameter expansion	2018-08-07 18:58:02 +02:00
ash_doc.txt
ash_ptr_hack.c
ash.c	ash: distinguish 'wait -n' from other bashisms	2019-04-02 13:43:40 +02:00
brace.txt
Config.src	hush: allow hush to run embedded scripts	2018-11-27 16:13:07 +01:00
cttyhack.c	config: update size information	2018-12-28 03:20:17 +01:00
hush_doc.txt
hush_leaktool.sh
hush.c	hush: add bash-compatible EPOCH variables	2019-04-16 18:29:52 +02:00
Kbuild.src
match.c
match.h
math.c
math.h
random.c
random.h
README
README.job
shell_common.c
shell_common.h

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.