Shell script to Find file size

Shell Programming and Scripting
1

Hi,
I am writing a script which takes the input file name and concat as a new file by appending a "1" to the file name. However i am not able to get the size of this new file. I am not sure where i am going wrong. Please check the script and help me get this working.

#!/bin/sh
FILE_NAME=$1
SIZE=$2

FILE_SIZE=`du -sk $FILE_NAME | cut -c1-2`

echo $FILE_SIZE

`cat $FILE_NAME >> $FILE_NAME$"1"`

FILE_SIZE=\`du -sk $FILE_NAME$"1" | cut -c1-2\`

echo $FILE_SIZE

Thanks
Rag

2 
#!/bin/ksh
# parms $1 = old file name
newfile="$1"1
cp $1 $newfile
du -sk $1 | read size1 dummy
du -sk $newfile | read size2 dummy
echo "files sizes: $1 = $size1  $newfile = $size2"