How to add a user/group and verify that the UID/GID is free?

[Johannes Puschmann <puschl puschl at>]

Hi!
I poking around hours with a specfile.
I must add a new User/group and will verify  that the UID/GID is unique 
and if not print  a  error message whats going on.


Is there a better way as grep the /etc/passwd such as getent?
I have tried getent, but when the uid is free, rpm fails with bad exit code.

The code:

die(){ %whinge "$*"; exit 1; }

 getent passwd %{gid}
#getent bring retval 2 and we have bad exit status.
#Any way to catch this ?

if   [ $? != 2 ] ; then die  \
	'An existing group is using GID %{gid}, we need it. ' \
	'Aborting build process.'

    /usr/sbin/groupadd  -g %{gid} -r %{group} || die \
	'Unexpected error adding group "%{group}" (GID %gid}). Aborting build \ 
process.'
else
    auid=`getent group %{group}`
    echo $auid | grep %{gid}
    if   [ $? != 0 ] ; then die \
	'"%{group}" group already exist but GID is not %{gid}. ' \
	'Aborting build process.'
   fi
fi

System is an RH 7.3

BTW:
Does somebody know, where the %whinge macro does came from ?
It not under /usr/lib/rpm