Shell中进行文件加锁,达到互斥

复杂锁shell代码：

?LOCKFILE="/tmp/lock"
if [ -f "$LOCKFILE" ]
then
?pid=`cat $LOCKFILE`
?[ -n "$pid" ] && ps -p $pid | grep $pid >/dev/null?
?[ $? -eq 0 ] && echo "script is running..." && exit 1
fi
?echo $$ > "$LOCKFILE"