Why this ftp script can not work properly?

[Sandglitter <gaolitao%gmail.com@localhost>]

Hi, It's me again~
I come to a problem that confuses me much:

I have written a ftp shell script to make my work easier, as follow:

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echo "-----FTP upload transmmision------" 
echo -n "\n  Please tell me ftp host address:"
read host 
echo -n "\n  Please input user name:"
read username 
echo -n "  Passwd required:" 
stty -echo　　　　　　　　　　　　　　　　　　　　　　　　　
read userpwd 
stty echo 
 
echo "\n  If you are sure, HIT enter or press Ctl+C"  
read goenter  

for file in `ls`  　　　　　　　　　　　
do  
 echo "File $file transmmision in progress......"  
 sh ftp_auto.sh $host 21 $username $userpwd $file $file      
 echo "OK" 
done  
echo "\nMission complete!!\n"  

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and my ftp_auto.sh is as follow:

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#!/bin/sh


ftp -niv $1 $2<<FTPIT 
quote USER $3
quote PASS $4

put $5 $6
bye
FTPIT

---------------------------------------------------------------

The strange thing is: the file with big size can not be uploaded completely!
but shell script output says that every file transfer is 100%!
I am sure that the file ftp server got is a little bit less than the original 
one, and if I use ftp command directly to upload the file, every thing is OK!

Is anyone familiar with this situation?