mysql备份脚本

!/bin/sh
# mysql_backup.sh: backup mysql databases and keep newest 5 days backup.
# -----------------------------
db_user="root"
db_passwd="linuxtone"
db_host="localhost"

# the directory for story your backup file.
backup_dir="/backup"

# date format for backup file (dd-mm-yyyy)
time="$(date +"%d-%m-%Y")"
######以上都是变量定义，$(date +"%d-%m-%Y")是引用date命令的结果
# mysql, mysqldump and some other bin's path
MYSQL="$(which mysql)"
MYSQLDUMP="$(which mysqldump)"
MKDIR="$(which mkdir)"
RM="$(which rm)"
MV="$(which mv)"
GZIP="$(which gzip)"
#########以上也是定义变量，有点区别的是这里都是命令变量的定义，防止直接用命令路径不对
#针对不同系统，如果环境变量都有。可以去掉

# check the directory for store backup is writeable
test ! -w $backup_dir && echo "Error: $backup_dir is un-writeable." && exit 0
#####条件测试语句：如果目录$backup_dir不可写则输出错误信息(echo)且退出(exit 0).
（&&的意思是前面的为真才执行后面的）；如果可写则执行下面语句。
# the directory for story the newest backup
test ! -d "$backup_dir" && $MKDIR "$backup_dir"
#####条件测试语句：如果目录$backup_dir不是目录，则创建该目录
# get all databases

for db in cdn cdn_view
do
        $MYSQLDUMP -u $db_user -h $db_host -p$db_passwd $db | $GZIP -9 > "$backup_dir/$time.$db.gz"
done
####for循环，mysqldump备份数据库cdn、cdn_view，而且指定了用户名、主机、密码，压缩为$backup_dir/$time.$db.gz
#delete the oldest backup 30 days ago
find $backup_dir -name "*.gz" -mtime +30 |xargs rm -rf
######find+xargs找到$backup_dir目录下后缀为.gz且30天没动过的文件，杀之
exit 0;      ######退出脚本