mirror of
https://github.com/sheumann/hush.git
synced 2024-11-01 10:06:40 +00:00
83 lines
2.0 KiB
Plaintext
83 lines
2.0 KiB
Plaintext
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.
|