一个小小的shell备份脚本

#!/bin/bash
olddir=“备份原目录”
newdir=“备份后目录”
cd $olddir
for filename in *
do
if ! cd $newdir 2> /dev/null
then
        echo "Can not find directory $newdir,backup fails." | mailx -s "Backup Notification" $USER
        exit
else
        cd $newdir
        if [ -e "$filename" ]
        then
                if diff $newdir/$filename $olddir/$filename > /dev/null
                then
                        :
                else
                        mv $newdir/$filename $newdir/$filename.$(date +%Y%m%d)
                        cp $olddir/$filename $newdir
                fi
        elif [ ! -e "$filename" ]
        then
                cp $olddir/$filename $newdir
        fi
fi
done