清空/var/log目录下的日志文件

#!/bin/bash
LOG_DIR=/var/log
ROOT_UID=0
LINES=50
#E_XCD＝66      ＃不能进入到目录时的退出代码值
E_NOTROOT=67
if [ "$UID" -ne "$ROOT_UID" ]
then
        echo "Must be root to run this script."
        exit $E_NOTROOT
fi
E_WRONGARGS=65
case "$1" in
"" ) lines=50;;
*[!0-9]*) echo "Usage:`basename $0` file-to cleanup";exit $E_WRONGARGS;;
*) lines=$1;;
esac
#上面测试命令行参数的功能也可如下实现。但上面更好
#if [ -n "$1" ]
#then
#       lines=$1
#else
#       lines=$LINES
#fi

cd $LOG_DIR

tail -$lines messages > mesg.temp
mv mesg.temp messages

echo "Logs cleaned up."
exit 0