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Re: Is this the expected behaviour for nameref in Bash 4.4 now?


From: Jack Kuan
Subject: Re: Is this the expected behaviour for nameref in Bash 4.4 now?
Date: Fri, 28 Oct 2016 17:41:27 -0400

thank you for the insight, it's very helpful!


On Oct 28, 2016 10:01 AM, "Chet Ramey" <address@hidden> wrote:
On 10/20/16 2:45 PM, address@hidden wrote:
> set -x
>
> var_123=123
> f() {
>     while (( $# )); do
>         shift
>         local var=var_123
>         local -n var=$var; : status is $?
>         local -p
>         : var is $var
>     done
> }
>
> f one two
>
>
> Running above script gives the follow output:
>
> + var_123=123
> + f one two
> + ((  2  ))
> + shift
> + local var=var_123
> + local -n var=var_123

`var' is a local nameref with value var_123

> + : status is 0
> + local -p
> var=var_123
> + : var is 123

Since var is a nameref, it expands to $var_123, which is 123

> + ((  1  ))
> + shift
> + local var=var_123

var doesn't get unset; it's still a nameref with value var_123.  Setting
the local attribute on an existing local variable doesn't unset any of
the variable's attributes.  You have to actually unset the variable to
do that.

> + local -n var=123
> ./x.sh: line 10: local: `123': invalid variable name for name reference

So now you try to assign `123' as the value of a nameref.  That would
cause subsequent attempts to assign to var to attempt to create and
assign to a variable named `123', which is invalid.  Bash-4.3 didn't
have enough error checking and would create variables with invalid names
in situations like this.

> + : status is 1
> + local -p
> var=var_123

This is probably where the confusion comes.  `local -p' doesn't print other
variable attributes.  If you had used `declare -p | grep var=' between the
two calls to `local' you would have seen that `var' had the nameref
attribute.

> + : var is 123
> + ((  0  ))

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


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