Shell 练习题

1.求100以内所有偶数之和
解析：本题主要考察如何遍历出100内所有偶数，并将其累加。

#!/bin/bash
#penman:liuyao
#Time:20190128
#求100以内所有偶数之和
#用到for循环得出100内的数；再用if条件判断100内的偶数；再做个累加。
#注意for后跟do/done 而if结束记得fi
#只要最后的结果，将输出写在done外,要每部的结果写在done前。
sum=0
for ((i=0;i<=100;i++))
do
if [ $((i%2)) -eq 0 ];then
((sum+=i))
fi
done
echo "All Even Number Sums Within 100 is : $sum"

运行结果
[root@localhost ~]# sh s1.sh
All Even Number Sums Within 100 is : 2550

2.写一个脚本，判断192.168.1.0/24网络中，当前在线的IP有哪些？
解析：如何判断当前某段ip有那些在线，可以将ping与echo $?结合来判断，学的好的可以对其进行优化。

#!/bin/bash
#Penman
#Time:20190130
for i in `seq 1 255`  #for循环i取1到255 
do 
   ping -c 1 192.168.1.$i &> /etc/null #ping结果错误重定向到/etc/null
#ift条件判断上部结果为0输出up，否则输出down。
   if [ $? -eq 0 ];then  
     echo -e "192,168.1.$i is up"
   else
     echo -e "192.168.1.$i is down"
   fi
done

运行结果
[root@localhost ~]# sh s2.sh
192.168.1.1 is down
192.168.1.2 is down
192.168.1.3 is down
192.168.1.4 is down

3.实现输入2个数和运算符的计算器
解析：本题看似简单但有好多要自己注意，如输入两个什么类型的数，及没有输入完整该如何等等，都需要自己去考虑与优化。

#!/bin/bash
#penman:liuyao
#Time:20190202
read -p "please input tow number :" a b 
read -p "please input operator :" c
if [ ! -z $b ] #判断第二个变量是否为空，为空则提示
then
  expr $a + $b &> /dev/null #判断输入的是否为整数，用expr让两个数相加不为整数的报错
    if [ $? -eq 0 ] 
    then 
      echo -e "result=$(($a $c $b))" 
    else
     echo -e "you must input zhengshu"
    fi
else
  echo -e "you must input tow number"
fi

运行结果
[root@localhost ~]# sh s3.sh
please input tow number :2 4
please input operator :+
result=6

4.显示一个菜单给用户：
cpu）display cpu information
mem）display memory information
disk）display disks information
quit）quit
要求：(1)提示用户给出自己的选择
           (2)正确的选择则给出相应的信息；否则，则提示重新选择正确的选项；
           提示：例如正确选择了cpu则输出cpu的信息
解析：本题要理解好题意，显示一个菜单选项，有两点要求提示用户及正确选项正确与否做出相应回应。

echo "Please enter your choice:
(cpu)    display cpu information
(mem)    display memory information
(disk)   display disks information
(quit)   quit" 
#判断了不选择则退出，选择错误则重选；
read -t 10 -p "your choice:" a
if [ -z "$a"  ];
 echo "Not choice ends `break`."
elif [ $a == cpu ];then
  cat /proc/cpuinfo
elif [ $a == mem ];then
  cat /proc/meminfo
elif [ $a == disk ];then
  fdisk -l
elif [ $a == quit ];then
  break   
else
  echo -e "Please enter again"
fi

运行结果
[root@localhost ~]# sh s4.sh
Please enter your choice:
(cpu) display cpu information
(mem) display memory information
(disk) display disks information
(quit) quit
your choice:Not choice ends .
[root@localhost ~]# sh s4.sh
Please enter your choice:
(cpu) display cpu information
(mem) display memory information
(disk) display disks information
(quit) quit
your choice:disk

Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
… … … …

5.写一个服务脚本：
变量$lockfile，变量值为：/var/lock/SCRIPT_NAME
(1)此脚本可接受start、stop、restart、status四个参数之一；
(2) 如果参数非此四者，则提示使用帮助后退出；
(3)start，则创建lockfile，并显示启动；stop，则删除lockfile，并显示停止；restart，则先删除此文件再创建此文件，而后显示重启完成；status，如果lockfile存在，则显示running，否则，则显示为stopped。
解析：SCRIPT_NAME脚本名;变量 $lockfile引用脚本名；下来注意逻辑顺序，可用输出验证是否正确。

#!/bin/bash
#Penman:liuyao
#Time:20190203
#运用if逻辑判断，主要在理解题。
SCRIPT_NAME=s5.sh
lockfile=/var/lock/$SCRIPT_NAME
read -p "Please input start or stop or restart or status :" a
if [ $a == start ];then
  if [ -f $lockfile ];then
      echo "$SCRIPT_NAME always is exit"
  else 
      touch $lockfile
      [ $? -eq 0 ] && echo -e "$SCRIPT_NAME is running"
  fi
elif [ $a == stop ];then
  if [ -f $lockfile ];then
    rm -rf $lockfile && echo -e "$SCRIPT_NAME is stop"
  else
    echo "$SCRIPT_NAME is not exit"
  fi
elif [ $a == restart ];then
  if [ -f $lockfile ];then
     rm -rf $lockfile && touch $lockfile
     echo -e "$SCRIPT_NAME is reboot succes"
  else 
     echo -e "$SCRIPT_NAME not exist"
  fi
elif [ $a == status ];then
  if [ -f $lockfile ];then
     echo -e "$SCRIPT_NAME is running"
  else
    echo -e "$SCRIPT_NAME is stopped"
  fi
else
   echo -e "input for start; stop; restart; status"
   break
fi 

运行结果
[root@localhost ~]# sh s5.sh
Please input start or stop or restart or status :1
input for start; stop; restart; status
[root@localhost ~]# sh s5.sh
Please input start or stop or restart or status :start
s5.sh is running
[root@localhost ~]# sh s5.sh
Please input start or stop or restart or status :stop
s5.sh is stop
[root@localhost ~]# sh s5.sh
Please input start or stop or restart or status :restart
s5.sh not exist
[root@localhost ~]# sh s5.sh
Please input start or stop or restart or status :status
s5.sh is stopped