On 01/04/2011 08:05 AM, Eric Blake wrote: > 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).
I found some other differences between shells: $ bash --posix -c 'cd /tmp; readonly PWD; echo $?; cd ..; echo $?-$PWD-$(pwd)' || echo abort,$? 0 bash: PWD: readonly variable 0-/tmp-/ $ bash -c 'cd /tmp; readonly PWD; echo $?; cd ..; echo $?-$PWD-$(pwd)' || echo abort,$? 0 bash: PWD: readonly variable 0-/tmp-/ $ ksh -c 'cd /tmp; readonly PWD; echo $?; cd ..; echo $?-$PWD-$(pwd)' || echo abort,$? 0 0-/-/ Bash goes ahead and changes the directory but leaves PWD untouched (PWD is now inconsistent without warning!) in both posix and bash mode, whereas ksh (silently) ignores the request to make PWD readonly in the first place. Also, both shells abort a non-interactive shell when readonly interferes with export (but bash only aborts in posix mode): $ ksh -c 'readonly v; export v=a; echo $?-$a' || echo abort,$? ksh: line 1: v: is read only abort,1 $ bash -c 'readonly v; export v=a; echo $?-$a' || echo abort,$? bash: v: readonly variable 1- $ bash --posix -c 'readonly v; export v=a; echo $?-$a' || echo abort,$? bash: v: readonly variable abort,1 I've gone ahead and filed a POSIX interpretation request: http://austingroupbugs.net/view.php?id=367 Also, since the next version of POSIX will be mandating changes for cd (http://austingroupbugs.net/view.php?id=253 adds the new cd -e option to warn if PWD is inconsistent), the notion of a readonly PWD may affect how you implement that proposal. -- Eric Blake ebl...@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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