#!/usr/bin/sh
cd /home/mmc/
for i in `ls PP02*`
do
l=`file $i|grep gzip|wc -l`

if [ $l -ne 0 ]; then
gunzip -c $i > /home/mmc/zip/$i
fi
done

ls file* | while read file
do
gzip "$file"
done

ls prefix* | while read f
do
   if ! gzip -t ${f} 2>/dev/null
   then
      gzip ${f} 
      # you might want to rename ${f}.gz to ${f} here
   fi
done

for i in `ls | xargs file | awk -F: '! /gzip/{print $1}'`
 do
    gzip $i
 done

#Now the files have the extension gz. If you need to move the files in a different directory afterwards:

for i in `ls | grep gz`
 do
   mv $i /home/other_dir/
 done

for i in `ls | xargs file | awk -F: '! /gzip/{print $1}'`