Shell Programming and Scripting

I want to find the size of particular file exists in a particular directory
and i wnt to zip it.
In the below mentioned code it should check the MQ.log in the
particular directory.Please correct my code so that it will check
for particular MQ.log but i could not able to check whether
the MQ.log exist and please tell me the way to check the file size also

ROTATE_FILES="/apps/Mesa/Logs/AE/AE_logs/test"
REAL_FILE="MQ.log"

function rotate_files()
{
for j in $1;do
if [ -d $j ];then
for i in `ls -a /$j`;do

if [ $i=MQ.log ];then
echo $i

$FILESIZE = `ls -l $i|awk '{print $5}'`
$LIMIT = 0

if [ $i -ge 0 ];then
echo "the size is greater"
fi
fi

done
fi
done
}

rotate_files "$ROTATE_FILES"