清除日志的shell脚本

#!/bin/bash
LOG_DIR=/var/log
ROOT_UID=0
LINES=50
E_XCD=66
E_NOTROOT=67

if [ "$UID" -ne "$ROOT_UID" ]
then
echo "Must be root to run this script."
exit $E_NOTROOT
fi
if [ -n "$1" ]
then
lines=$1
else
lines=$LINES
fi
cd $LOG_DIR
if [ `pwd` != "$LOG_DIR" ]
             
then
echo "Can't change to $LOG_DIR."
exit $E_XCD
fi
tail -$lines messages > mesg.temp
mv mesg.temp messages
echo "Logs cleaned up."
exit 0