Re: Bash silently exits where attempting to assign an array to certain built-in variables using declare

[Chet Ramey]

On 6/28/23 1:14 PM, Kerin Millar wrote:
> This report is based on an observation made within the depths of this thread: 
> https://lists.gnu.org/archive/html/bug-bash/2023-06/msg00094.html.
>
> Attempting to assign an array to any of the following variables with the 
> declare builtin causes bash to immediately exit with no diagnostic message 
> being issued.
>
>    BASH_ARGC
>    BASH_ARGV
>    BASH_LINENO
>    BASH_SOURCE
>    GROUPS

These are all `noassign' variables; assignments to them are ignored.
The bash debugger variables cannot be unset either. Other noassign
variables can be unset; that's why they're not readonly.

(Before you ask, noassign variables have been in bash since 1996.)

In this case, assignment to the noassign variable is being treated like an
assignment error, which aborts the current command (a compound command in
your examples) but does not exit the shell. If you were to separate the
commands with a newline, you'd see the difference.

This came up in 2021 in the GROUPS case:

https://lists.gnu.org/archive/html/bug-bash/2021-08/msg00013.html

The other variables in that list inherited their noassign property from
changes to support the bash debugger.

> It does not happen if trying to assign a string.

It should be consistent, at least. I think the string assignment behavior
is the most reasonable: assignments return 1 but there's no assignment
error. I'll look at how compound assignments are different.

>    $ bash -c 'declare BASH_ARGC=1; echo FIN'
>    FIN
>
> There are various other variables bearing the readonly attribute for which this 
> also happens. In the following case, bash does, at least, complain that the 
> variable is readonly.
>
>    $ bash -c 'declare BASHOPTS=(); echo FIN'
>    bash: line 1: BASHOPTS: readonly variable

Attempted assignment to readonly variables is an assignment error.

> This seems rather inconsistent. Also, it is confusing for bash to quit without 
> indicating why it did so.

Technically, it exited because it hit EOF after aborting the compound
command.

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