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

From: Roman Rakus
Subject: Re: using the variable name, GROUPS, in a read list
Date: Wed, 07 Mar 2012 17:05:20 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120216 Thunderbird/10.0.1

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

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

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 $?


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