Re: [PATCH] Enable further expansion of parameter name by ${!...}

[ZyX <kp-pav@yandex.ru>]

26.01.2015, 23:01, "Tomoki Sekiyama" <tomoki.sekiyama@gmail.com>:
> Hi all,
> Thank you for your comments.
>>  IIRC, in bash, you can also use ${!foo} even with banghist active. We
>>  probably don't want to replicate that feature, but make sure ${\!foo}
>>  works I suppose?
>
> Right, I don't think we want to change banghist behavior when it is active.
> We can avoid banghist by ${\!foo} when it is active.
>
> 2015-01-25 16:39 GMT-05:00 Bart Schaefer <schaefer@brasslantern.com>:
>>  On Jan 25, 11:38pm, ZyX wrote:
>>  } Subject: Re: [PATCH] Enable further expansion of parameter name by ${!...}
>>  }
>>  } 25.01.2015, 23:25, "Bart Schaefer" <schaefer@brasslantern.com>:
>>  } >
>>  } > Don't we already have something like this for ksh emulation?  Except that
>>  } > it acts like (k) instead of like (P)?  Although I can't find this in the
>>  } > documentation anywhere, right at the moment.
>>  }
>>  } I have ksh installed and here `${!VAR}` outputs `VAR` regardless of
>>  } whether $VAR is defined and what type and what value does it have.
>>
>>  I thought I recalled something about that.  So it would appear that
>>  whatever interpretation we're giving it already in ksh mode, is wrong.
>>
>>  } [Manual page][1] says that it should actually expand to "the name of
>>  } the variable referred to by vname" and says that this will be `VAR`
>>  } unless it is a name reference (I have only tried strings, arrays and
>>  } associative arrays).
>>  }
>>  } [1]: http://unixhelp.ed.ac.uk/CGI/man-cgi?ksh+1
>
> I have tried some patterns with ksh and bash.
>
> ### Variable reference
> aaa=bbb
> bbb=ccc
>                     # ksh       bash     zsh(default)       zsh(KSH)
> echo $aaa           # bbb       bbb      bbb                bbb
> echo ${!aaa}        # aaa       ccc      bad substitution   bbb
>
> ### Assoc
> typeset -A foo
> foo[bar]=baz
> foo["baz"]="qux"
> baz=piyo
>                     # ksh       bash     zsh(default)       zsh(KSH)
> echo $foo           #                    baz qux
> echo ${foo[bar]}    # baz       baz      baz                baz
> echo ${foo["bar"]}  # baz       baz
> echo ${foo[baz]}    # qux       qux
> echo ${foo["baz"]}  # qux       qux      qux                qux
> echo ${!foo[bar]}   # foo[bar]  piyo     bad substitution   bar
> echo ${!foo["bar"]} # foo[bar]  piyo     bad substitution
> echo ${!foo[@]}     # bar baz   bar baz  bad substitution  "baz" bar
>
> It seems that ${!...} in KSH emulation mode of zsh is only useful for the case
> of "${!foo[@]}", which is substituted with the list of keys of the assoc,
> that has the same meaning also in bash.
> (Although zsh regards baz and "baz", or even 'baz' as different keys...)

Quote removal is not done in subscripts. In bash you may have `baz`, `'baz'` and `"baz"` and due to quote removal it computes to just `baz`. This is explicitly mentioned in the seventh paragraph of Subscript Parsing subsection of ARRAY PARAMETERS section of `man zshparam`.

>
> According to this, introducing bash-like behaviors instead of "bad
> substitution" error will
> not hurt zsh even in ksh emulation mode.
>
> Any comments are appreciated.
>
> Thanks,
> Tomoki