| 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. |
