df ksh and exclude a filesystem

I have df -k file system monitor script below.  What I need is to exclude /backup filesystem because it is always around 98 or 99%.   How do you put the line for excluding the /backup?

bla...

ALERT_ADMIN () { mail -s "${MAIL_SUBJ}"  $DIST_LIST  << EOF
Filesystem $fsname has reached $sz% of its capacity.
EOF
return
}

cd . > $WORKDIR/freespace.lst
exec 8< $WORKDIR/freespace.lst

df -k | grep -v -i filesystem | grep -v ":" | awk '{print $7,substr($4,1,2)}' |
grep -v "%" | grep -v proc > $WORKDIR/freespace.lst

if [ -f $WORKDIR/freespace.lst ]
then
 while read -u8 fsname sz ;
   do
   if [[ $sz -gt $WARNLEVEL ]]
     then
        ALERT_ADMIN
    fi
done
fi


thx much

      Start Free Trial