[3320] | 1 | http://www.opengroup.org/onlinepubs/9699919799/
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| 2 | Open Group Base Specifications Issue 7
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| 3 |
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| 4 |
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| 5 | http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap01.html
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| 6 | Shell & Utilities
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| 7 |
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| 8 | It says that any of the standard utilities may be implemented
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| 9 | as a regular shell built-in. It gives a list of utilities which
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| 10 | are usually implemented that way (and some of them can only
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| 11 | be implemented as built-ins, like "alias"):
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| 12 |
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| 13 | alias
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| 14 | bg
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| 15 | cd
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| 16 | command
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| 17 | false
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| 18 | fc
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| 19 | fg
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| 20 | getopts
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| 21 | jobs
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| 22 | kill
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| 23 | newgrp
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| 24 | pwd
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| 25 | read
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| 26 | true
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| 27 | umask
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| 28 | unalias
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| 29 | wait
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| 30 |
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| 31 |
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| 32 | http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
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| 33 | Shell Command Language
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| 34 |
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| 35 | It says that shell must implement special built-ins. Special built-ins
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| 36 | differ from regular ones by the fact that variable assignments
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| 37 | done on special builtin are *PRESERVED*. That is,
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| 38 |
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| 39 | VAR=VAL special_builtin; echo $VAR
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| 40 |
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| 41 | should print VAL.
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| 42 |
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| 43 | (Another distinction is that an error in special built-in should
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| 44 | abort the shell, but this is not such a critical difference,
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| 45 | and moreover, at least bash's "set" does not follow this rule,
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| 46 | which is even codified in autoconf configure logic now...)
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| 47 |
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| 48 | List of special builtins:
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| 49 |
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| 50 | . file
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| 51 | : [argument...]
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| 52 | break [n]
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| 53 | continue [n]
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| 54 | eval [argument...]
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| 55 | exec [command [argument...]]
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| 56 | exit [n]
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| 57 | export name[=word]...
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| 58 | export -p
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| 59 | readonly name[=word]...
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| 60 | readonly -p
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| 61 | return [n]
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| 62 | set [-abCefhmnuvx] [-o option] [argument...]
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| 63 | set [+abCefhmnuvx] [+o option] [argument...]
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| 64 | set -- [argument...]
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| 65 | set -o
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| 66 | set +o
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| 67 | shift [n]
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| 68 | times
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| 69 | trap n [condition...]
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| 70 | trap [action condition...]
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| 71 | unset [-fv] name...
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| 72 |
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| 73 | In practice, no one uses this obscure feature - none of these builtins
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| 74 | gives any special reasons to play such dirty tricks.
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| 75 |
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| 76 | However. This section also says that *function invocation* should act
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| 77 | similar to special built-in. That is, variable assignments
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| 78 | done on function invocation should be preserved after function invocation.
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| 79 |
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| 80 | This is significant: it is not unthinkable to want to run a function
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| 81 | with some variables set to special values. But because of the above,
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| 82 | it does not work: variable will "leak" out of the function.
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