Denys Vlasenko c5a1be25ba ash: fix handling of single-quoted strings in pattern substitution 1 month ago
..
ash_test c5a1be25ba ash: fix handling of single-quoted strings in pattern substitution 1 month ago
hush_test c5a1be25ba ash: fix handling of single-quoted strings in pattern substitution 1 month ago
Config.src 67e1529b92 nologin: make it possible to build it as single applet 3 years ago
Kbuild.src 0b8835861b Make it possible to select "sh" and "bash" aliases without selecting ash or hush 7 years ago
README 131ed3bcc9 update shell/README 14 years ago
README.job 5f786c24e4 hush: small code shrink; style fixes 17 years ago
ash.c c5a1be25ba ash: fix handling of single-quoted strings in pattern substitution 1 month ago
ash_doc.txt b21f379639 ash: fix TRACE commands 15 years ago
ash_ptr_hack.c 0ef64bdb40 *: make GNU licensing statement forms more regular 13 years ago
ash_remove_unnecessary_code_in_backquote_expansion.patch 4c4b02c290 ash: save Ron's patch from oblivion 2 years ago
brace.txt 647553a4fc hush: wait for `cmd` to complete, and immediately store its exitcode in $? 14 years ago
cttyhack.c 5353df91cb Update applet size estimates 8 months ago
hush.c 758b21402a hush: detect when terminating "done"/"fi" is missing 1 month ago
hush_doc.txt bcb25537d0 hush: implement break and continue 15 years ago
hush_leaktool.sh dcd78c4d0f hush: fix "export not_yet_defined_var", fix parsing of "cmd | }" 15 years ago
match.c 9b6f44e040 style fix 1 year ago
match.h 701e127f7d hush: optimize #[#] and %[%] for speed. size -2 bytes. 13 years ago
math.c cc9543fed1 shell/math: avoid $((3**999999999999999999)) to take years 8 months ago
math.h 19a74a54de shell/math: change ?: nesting code to not have 63 level nesting limitation 9 months ago
random.c 4c201c00a3 whitespace fixes 5 years ago
random.h fb183076a3 ash,hush: improve randomness of $RANDOM, add easy-ish way to test it 10 years ago
shell_common.c 96769486e2 shell: move varcmp() to shell_common.h and use it in hush 9 months ago
shell_common.h 96769486e2 shell: move varcmp() to shell_common.h and use it in hush 9 months ago

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.