| 1 | http://www.opengroup.org/onlinepubs/9699919799/
|
|---|
| 2 | Open Group Base Specifications Issue 7
|
|---|
| 3 |
|
|---|
| 4 |
|
|---|
| 5 | http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html
|
|---|
| 6 | Shell & Utilities
|
|---|
| 7 |
|
|---|
| 8 | It says that any of the standard utilities may be implemented
|
|---|
| 9 | as a regular shell built-in. It gives a list of utilities which
|
|---|
| 10 | are usually implemented that way (and some of them can only
|
|---|
| 11 | be implemented as built-ins, like "alias"):
|
|---|
| 12 |
|
|---|
| 13 | alias
|
|---|
| 14 | bg
|
|---|
| 15 | cd
|
|---|
| 16 | command
|
|---|
| 17 | false
|
|---|
| 18 | fc
|
|---|
| 19 | fg
|
|---|
| 20 | getopts
|
|---|
| 21 | jobs
|
|---|
| 22 | kill
|
|---|
| 23 | newgrp
|
|---|
| 24 | pwd
|
|---|
| 25 | read
|
|---|
| 26 | true
|
|---|
| 27 | umask
|
|---|
| 28 | unalias
|
|---|
| 29 | wait
|
|---|
| 30 |
|
|---|
| 31 |
|
|---|
| 32 | http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
|
|---|
| 33 | Shell Command Language
|
|---|
| 34 |
|
|---|
| 35 | It says that shell must implement special built-ins. Special built-ins
|
|---|
| 36 | differ from regular ones by the fact that variable assignments
|
|---|
| 37 | done on special builtin are *PRESERVED*. That is,
|
|---|
| 38 |
|
|---|
| 39 | VAR=VAL special_builtin; echo $VAR
|
|---|
| 40 |
|
|---|
| 41 | should print VAL.
|
|---|
| 42 |
|
|---|
| 43 | (Another distinction is that an error in special built-in should
|
|---|
| 44 | abort the shell, but this is not such a critical difference,
|
|---|
| 45 | and moreover, at least bash's "set" does not follow this rule,
|
|---|
| 46 | which is even codified in autoconf configure logic now...)
|
|---|
| 47 |
|
|---|
| 48 | List of special builtins:
|
|---|
| 49 |
|
|---|
| 50 | . file
|
|---|
| 51 | : [argument...]
|
|---|
| 52 | break [n]
|
|---|
| 53 | continue [n]
|
|---|
| 54 | eval [argument...]
|
|---|
| 55 | exec [command [argument...]]
|
|---|
| 56 | exit [n]
|
|---|
| 57 | export name[=word]...
|
|---|
| 58 | export -p
|
|---|
| 59 | readonly name[=word]...
|
|---|
| 60 | readonly -p
|
|---|
| 61 | return [n]
|
|---|
| 62 | set [-abCefhmnuvx] [-o option] [argument...]
|
|---|
| 63 | set [+abCefhmnuvx] [+o option] [argument...]
|
|---|
| 64 | set -- [argument...]
|
|---|
| 65 | set -o
|
|---|
| 66 | set +o
|
|---|
| 67 | shift [n]
|
|---|
| 68 | times
|
|---|
| 69 | trap n [condition...]
|
|---|
| 70 | trap [action condition...]
|
|---|
| 71 | unset [-fv] name...
|
|---|
| 72 |
|
|---|
| 73 | In practice, no one uses this obscure feature - none of these builtins
|
|---|
| 74 | gives any special reasons to play such dirty tricks.
|
|---|
| 75 |
|
|---|
| 76 | However. This section also says that *function invocation* should act
|
|---|
| 77 | similar to special built-in. That is, variable assignments
|
|---|
| 78 | done on function invocation should be preserved after function invocation.
|
|---|
| 79 |
|
|---|
| 80 | This is significant: it is not unthinkable to want to run a function
|
|---|
| 81 | with some variables set to special values. But because of the above,
|
|---|
| 82 | it does not work: variable will "leak" out of the function.
|
|---|
