shell的基本語句（for迴圈，while迴圈，巢狀迴圈，if 的多重迴圈，case語句）
阿新 • • 發佈：2018-12-26
1.for迴圈（遍歷）
for 條件
do
動作
done
練習1：檢測當前172.25.254網段主機的狀態
[[email protected] mnt]# vim test.sh 1 #!/bin/bash 2 for ((IP=1;IP<=10;IP++)) 3 do { 4 ping -c1 -w1 172.25.254.$IP &> /dev/null && echo "172.25.254.$IP is up" || echo "172.25.254.$IP is down" 5 } 6 done
[[email protected] mnt]# sh test.sh
練習2：寫一個10秒的倒計時
[[email protected] mnt]# vim time.sh
10 #!/bin/bash
11 for((i=10;i>=0;i--))
12 do {
13 echo -n "time $i "
14 echo -ne "\r"
15 sleep 1
16 }
17 done
[[email protected] mnt]# sh time.sh
練習3：寫一個使用者自定義分秒的倒計時
[[email protected] mnt]# vim time.sh 10 #!/bin/bash 11 read -p "please input a time:" a b 12 13 for((i=$a*60+$b;i>=0;i--)) 14 do { 15 m=$[$i/60] 16 n=$[$i%60] 17 echo -n "time $m:$n " 18 echo -ne "\r" 19 sleep 1 20 } 21 done
[[email protected] mnt]# sh time.sh
please input a time:1 5
2.while迴圈
while true 條件為真就執行
do
done
[[email protected] mnt]# uptime # 檢視系統開啟了多長時間
14:31:41 up 5:33, 2 users, load average: 0.00, 0.02, 0.05
[[email protected] mnt]# echo "student" | passwd --stdin student # 非互動修改使用者密碼
練習1：批量建立使用者，並非互動式修改使用者密碼
[[email protected] mnt]# vim while.sh
10 #!/bin/bash
11 PREFIX="LALA"
12 i=1
13 while [ $i -le 3]
14 do
15 useradd ${PREFIX}$i
16 echo "123" | passwd --stdin ${PREFIX}$i &> /dev/null
17 ((i++))
18 done
[[email protected] mnt]# sh while.sh
3.巢狀迴圈
練習：列印9*9乘法表
[[email protected] mnt]# vim multiply.sh
10 #!/bin/bash
11 for((i=1;i<=9;i++))
12 do
13 for((j=1;j<=i;j++))
14 do
15 t=$[i*j]
16 echo -ne $j*$i=$t "\t"
17 done
18 echo -e "\n"
19 done
[[email protected] mnt]# sh multiply.sh
4.if-else 迴圈
If 條件；then
動作1
elif
動作2
else
動作3
fi
[[email protected] mnt]# vim if_else_elif.sh
10 #!/bin/bash
11 read -p "please input your score:" s
12 if [ "$s" -lt "60" ];then
13 echo you are not pass!!
14 elif [ "$s" -ge "60" -a "$s" -lt "80" ];then
15 echo you are good!!
16 elif [ "$s" -ge "80" ];then
17 echo you are best!!
18 else
19 echo you are not have score!!
20 fi
[[email protected] mnt]# sh if_else_elif.sh
5.case 語句
case num in
條件1) #可以判斷多條
命令1
;;
條件2)
命令2
esac
練習：編寫一個指令碼,實現如下功能
[[email protected] mnt]# vim case.sh
10 #!/bin/bash
11 echo -e "
12 \033[036m A 顯示主機IP \033[0m
13 \033[032m B 顯示磁碟剩餘空間 \033[0m
14 \033[033m C 顯示系統執行時間 \033[0m
15 \033[034m Q 退出 \033[0m
16 "
17 for ((i=1;;i++))
18 do
19 read -p "please input a letter:" a
20 case $a in
21 a|A)
22 echo -e "\n `ifconfig eth0 | grep "inet "| cut -d " " -f 10`"
23 ;;
24 B|b)
25 echo -e "\n `df | awk -F " " '{if(NR==2){ print "系統剩餘空間為:"$4}}'` "
26 ;;
27 C|c)
28 echo -e "\n `uptime | awk '{print $3}'|awk -F, '{print $1}'|awk -F: '{ p rint "系統已經運行了" $1 "小時" $2 "分鐘"}'`"
29 ;;
30 Q|q)
31 exit 0
32 ;;
33 *)
34 echo -e "\033[31m \nError \033[0m";;
35 esac
36 done
[[email protected] mnt]# sh case.sh
練習：編寫httpd監控指令碼，要求可以輸入start|stop|restart|status
[[email protected] mnt]# vim httpd.sh
10 #!/bin/bash
11 echo -e "
12 \033[036m start 開啟httpd \033[0m
13 \033[032m status 檢視httpd的狀態 \033[0m
14 \033[033m stop 關閉httpd \033[0m
15 \033[034m restart 重啟httpd \033[0m
16 \033[035m quit 退出 \033[0m
17
18 "
19 for ((i=1;;i++))
20 do
21 read -p "please input a letter:" a
22 case $a in
23 start)
24 systemctl start httpd
25 echo 您已成功開啟httpd
26 ;;
27 status)
28 systemctl status httpd
29 ;;
30 stop)
31 systemctl stop httpd
32 echo 您已成功關閉httpd
33 ;;
34 restart)
35 systemctl restart httpd
36 echo 您已重啟成功
37 ;;
38 q|Q)
39 exit 0
40 ;;
41 *)
42 echo -e "\033[31m \nError \033[0m";;
43 esac
44 done
[[email protected] mnt]# sh httpd.sh
