Re: using the variable name, GROUPS, in a read list

[Roman Rakus]

On 03/07/2012 04:54 PM, Jim Meyering wrote:
> FYI, if I attempt to read into the built-in array variable, GROUPS,
> this doesn't work:
>
>    $ bash -c 'while read GROUPS; do echo $GROUPS; done<  /etc/passwd'|wc -l
>    0
>
> Comparing with dash, I see what the author expected, i.e.,
> that the while loop iterates once per line in /etc/passwd:
>
>    $ dash -c 'while read GROUPS; do echo $GROUPS; done<  /etc/passwd'|wc -l
>    57
>
> With bash, I can work around that by first doing "unset GROUPS".
>
> Is there a moral here, other than to avoid using special variable names?
> Probably to prefer lower-case variable names.
GROUPS An  array  variable  containing  the list of groups of which the
              current user is a member.  Assignments to GROUPS have no  
effect
              and  return  an  error status.  If GROUPS is unset, it 
loses its
              special properties, even if it is subsequently reset.

$ read GROUPS <<< "a"; echo $?
1

RR