How to get the modified files(before and after) from git version server?

Thanks all, I have found the correct way, here it is.

#!/bin/bash
from_id=$1
to_id=$2
#echo $from_id
#echo $to_id
diffpath='patch/diff.log'
newpath='patch/new/'
oldpath='patch/old/'
rm -rf patch
mkdir -p $newpath
mkdir -p $oldpath
git diff $from_id $to_id --raw > $diffpath
cat $diffpath | while  read line
do 
    #echo =====================================
    #echo $line
    OLD_IFS="$IFS"
    IFS=" "
    arr=($line)
    IFS="$OLD_IFS"   
    #echo ${arr[4]}
    filepath=${arr[4]##* }
    #echo $filepath
    newid=${arr[2]%%...}
    #echo $newid
    oldid=${arr[3]%%...}
    #echo $oldid  

   if [ "$newid"x != "0000000"x  ]; then   
     newfilepath=${newpath}${filepath}
     echo $newfilepath
     dirpath=${newfilepath%/*}
     echo $dirpath
     mkdir -p ${dirpath}
     git cat-file -p $newid >  ${newfilepath}
   fi

   if [ "$oldid"x != "0000000"x  ]; then 
     oldfilepath=${oldpath}${filepath} 
     echo $oldfilepath
     dirpath=${oldfilepath%/*}
     echo $dirpath   
     mkdir -p ${dirpath}
     git cat-file -p $oldid >  ${oldfilepath}
   fi   
done 

You will found the new directory named patch in current working directory after doing this.