I dont know what you want but i think i knw what you mean

try this (Googled it , just like you did) lolol
ctr=1
for i in *
do
var1=`file $i |awk '{printf "%s\n",$3}'`
if [ $var1 = "text" ]; then
filename=`ls $i | cut -f1 -d "."`
ext=`ls $i |awk -F "." '{printf "%s\n",$2}'`
mv $i $filename$ctr.$ext
ctr=`expr $ctr + 1`
fi
done