On Tue, Aug 18, 2009 at 10:37 AM, Jan Ingvoldstad<[email protected]> wrote:
>> It's not that unreasonable.
>
> I disagree, and I think I've explained why, and perhaps we won't get much
> further.
I'm not claiming that it's a good idea for bash to adopt this
behavior, only that it's a reasonable expectation tohave upon
encountering the read behavior of $PWD.
Its not unlike, say, applying an UPDATE to a view in an RDBMS: it
seems like it should work. It might not, for various reasons, but
it's not an unreasonable expectation. And in many versions of SQL it
does work for the simpler view/table relationships.
>> But USER isn't even a shell-maintained variable.
>
> I'm not sure what you mean by a "shell-maintained variable".
I mean, it's not a parameter that is ever set by the shell. Unlike
PWD, RANDOM, LINENO, PPID, etc. which are set by the shell.
> As for $UID being read-only, that's a bashism. There's nothing inherent
> about $UID that makes it read-only.
Huh? I thought UID was a bashism. In my copies of ksh, it's not even
set - AT&T ksh93 (version M 1993-12-28 s+ under UWIN, Version JM 93t+
2009-05-01
on Linux) and pdksh 5.2.14. . If it's POSIX, it must be a a
relatively recent addition.
> In a POSIX shell, you get this:
>
> $ ksh --version
> version sh (AT&T Research) 1993-12-28 s+
> $ echo $UID $USER
> 501 jani
Not here.
> bash in POSIX mode agrees:
What version of bash? bash-3.2:
$ bash --posix
bash-3.2$ echo $UID
1024
bash-3.2$ UID=500
bash: UID: readonly variable
Did you maybe export UID, so it's being inherited by these subshells?
> Even Perl 5 lets me change it:
OK, you clearly exported UID. It's not exported by default, so
$ENV{UID} in Perl should be unset. Try your experiments without
exporting UID.
In any case, %ENV isn't readonly in Perl. But neither are the contents
of %ENV managed by Perl - just inherited from the parent process.
--
Mark J. Reed <[email protected]>
