shell最多支持多少重if嵌套啊，有没得像and or

小弟今天做了一个定时关机的shell，涉及到时间判定的问题，没有找到and or之类的逻辑语句，所用了多重if嵌套，但是语句通不过检测，请各位大虾帮忙看看啊！
shell如下：
#!/bin/sh
WEEK=`date +%H`
MINTE=`date +%M`
#the judge for hour
if $WEEK -gt 7
  then
   echo  "the time passed ,wait next time,halting    ..."
else
   if $WEEK -lt 6
    then
     echo  "too early to start,have a good rest,system is halting ..."
      if $MINTE -gt 30
         then
          echo "the time is too late ,wait for the next time "
        fi
     fi
fi
if $WEEK -lt 11
   then
   echo  "the time is not come,wait ...,system is halted..."
else
   if $WEEK -gt 13
    then  
    echo "the time is lost ,the system is halting..."   
   fi
   if $MINTE -lt 30
     then
     echo "the time is too ealier,wait a moment"
fi
fi


if $WEEK -lt 17
   then
   echo  "the time is not come,wait ...,system is halted..."
   if $MINTE -lt 30
      then
      echo "the is is too early,wait a moment..."
   fi
else
   if $WEEK -gt 18
     then
      echo "the time is over ,waiting for the system halting..."
      if $NINTE -gt 30
         then
          echo "the time is too late ,waiting for shutdwon..."
          fi
     fi
fi

if $WEEK -lt 21
   then
   echo  "the time si not come,wait ...,system is halted..."
else
   if $WEEK -lt 23
   then
   echo  "the time is ower ,waiting for the system halting..."     
   fi
fi

and or之类的逻辑语句有：
字符：
if [ string1 -a string2 ] string1 and string2
if [ string1 -o string2 ] string1 or string2
关系：
if [ [ pattern1 && pattern2 ] ] pattern1 and pattern2
if [ [ pattern1 || pattern2 ] ] pattern1 or pattern2

是这样的啊，和C的逻辑差不多啊