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Re: Unset array doesn't work

From: Chet Ramey
Subject: Re: Unset array doesn't work
Date: Tue, 27 Feb 2018 11:18:40 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 2/26/18 4:31 AM, Robert Elz wrote:
>     Date:        Mon, 12 Feb 2018 09:26:37 -0500
>     From:        Chet Ramey <address@hidden>
>     Message-ID:  <address@hidden>
>   | This is bash's dynamic scoping. The visibility of a local variable is
>   | restricted to a function and its children, and `unset' removes the
>   | currently-visible instance. Removing such an instance can `unconver' an
>   | instance in a previous scope.
> Frankly this is brain dead, unset should not be unlocal (or something equiv)
> eg: if I have a func
>       myfunc() {
>               local IFS
>               unset IFS
>               # do some code
>       }
> the very last thing that I want is for the global IFS to apply.

It doesn't. Run the following script:

        local var=$'a\tb\tc'
        typeset IFS=' '

        echo ${FUNCNAME}: before unset: $var
        unset IFS
        echo ${IFS:-null or unset}
        echo ${FUNCNAME}: after unset: $var

declare -p IFS
declare -p IFS

You'll see that the first expansion of `$var' uses the local value of IFS,
the second expansion uses the default value of $' \t\n', and the global
value doesn't change (or get unset) outside the function.

The objection was that the global or previous-scope value didn't get unset
when using the `unset' builtin; only in the local scope was it unset.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/

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