Re: read builtin and readonly variables

[Eric Blake]

On 01/03/2011 11:41 PM, Jan Schampera wrote:
> Hello list,
> 
> 
> the read builtin command, when trying to assign to a readonly variable
> after reading the data, spits an error message. This is fine.
> 
> But the return status is 0. It "always" (down to 2.04 was tested) has
> been like that, and it's like that in upcoming 4.2.
> 
> For me, this doesn't make sense. The read may have been successful, but
> the data is gone. It would make sense to return !=0 here, IMHO.

getopts also suffers from a difference in behavior between shells on
readonly arguments:

$ ksh -c 'readonly foo; getopts a: foo -a blah; echo $?'
ksh[1]: ksh: foo: is read only
$ echo $?
2
$ bash -c 'readonly foo; getopts a: foo -a blah; echo $?'
bash: foo: readonly variable
1

where non-interactive ksh completely exited on an invalid assignment,
but bash merely set $?.

> 
> I also quickly cross-read POSIX, since such weirdness usually comes from
> there ;-) but I didn't see anything obvious.

I couldn't find anything either - the POSIX wording for readonly only
mentions assignment and unset as requiring errors.  I think that's an
unintentional hole in POSIX, though, so I'm going ahead and submitting a
bug report to have readonly also mention read and getopts as being
required to error out on a readonly variable (and given that ksh treats
assignment different than unset on whether a non-interactive shell
exits, the extent of the reaction for getopts and read will probably
have to allow both behaviors).

-- 
Eric Blake   eblake@redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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