20.10 for循环
·语法：for 变量名 in 条件; do …; done
案例1
计算1到100数字的和
#!/bin/bash sum=0 for i in `seq 1 100` do sum=$[$sum+$i] ##核心语句 echo $i done echo $sum
案例2
列出/etc/下的目录或子目录
#!/bin/bash cd /etc/ for a in `ls /etc/` do if [ -d $a ] then ls -d $a fi done
ls 是用空格或回车作为分隔符，for循环以他对象，那么可能会出错
20.11/20.12 while循环
·语法 while 条件; do … ; done
案例1
#!/bin/bash
while : ## : 表示死循环 或者写成 while true
do
load=`w|head -1|awk -F 'load average: ' '{print $2}'|cut -d. -f1`
if [ $load -gt 10 ]
then
top|mail -s "load is high: $load" [email protected]
##或/usr/local/sbin/mail.py [email protected] "load high" "$load"
fi
sleep 30
done
案例2
#!/bin/bash while : do read -p "Please input a number: " n if [ -z "$n" ] then echo "you need input sth." continue ## continue 指继续重新再来一遍循环 fi n1=`echo $n|sed 's/[0-9]//g'` if [ -n "$n1" ] then echo "you just only input numbers." continue ## continue 从头继续重新再来一遍循环 fi break ##退出 while 循环 done echo $n
20.13 break跳出循环
#!/bin/bash for i in `seq 1 5` do echo $i if [ $i == 3 ] ##正常等于号应该写为 -eq，字符串等于为 == then break fi echo $i done echo aaaaaaa
[[email protected] shell]# sh -x break.sh ++ seq 1 5 + for i in '`seq 1 5`' + echo 1 1 + '[' 1 == 3 ']' + echo 1 1 + for i in '`seq 1 5`' + echo 2 2 + '[' 2 == 3 ']' + echo 2 2 + for i in '`seq 1 5`' + echo 3 3 + '[' 3 == 3 ']' + break + echo aaaaaaa aaaaaaa
原本在 i 为 3 之前，脚本一直执行到done，然后在从头循环，而 为 3 时，之间break跳出循环，
echo aaaaaaa
·break 用在循环语句里，for 也行，while 也行
20.14 continue结束本次循环
·忽略continue之下的代码，直接进行下一次循环
#!/bin/bash for i in `seq 1 5` do echo $i if [ $i == 3 ] then continue fi echo $i done echo $i
[[email protected] shell]# sh -x continue.sh ++ seq 1 5 + for i in '`seq 1 5`' + echo 1 1 + '[' 1 == 3 ']' + echo 1 1 + for i in '`seq 1 5`' + echo 2 2 + '[' 2 == 3 ']' + echo 2 2 + for i in '`seq 1 5`' + echo 3 3 + '[' 3 == 3 ']' ## 等于3时，直接结束了本次循环，从头开始 + continue + for i in '`seq 1 5`' + echo 4 4 + '[' 4 == 3 ']' + echo 4 4 + for i in '`seq 1 5`' + echo 5 5 + '[' 5 == 3 ']' + echo 5 5 + echo aaaaaaa aaaaaaa
·break会跳出循环，不再执行循环，而continue会结束本次循环，从头开始执行循环
20.15 exit退出整个脚本
exit直接退出脚本：
#!/bin/bash for i in `seq 1 5` do echo $i if [ $i == 3 ] then exit fi echo $i done echo aaaaa
[[email protected] shell]# sh -x exit.sh ++ seq 1 5 + for i in '`seq 1 5`' + echo 1 1 + '[' 1 == 3 ']' + echo 1 1 + for i in '`seq 1 5`' + echo 2 2 + '[' 2 == 3 ']' + echo 2 2 + for i in '`seq 1 5`' + echo 3 3 + '[' 3 == 3 ']' + exit
原文地址：http://blog.51cto.com/11530642/2105565
时间： 2024-10-14 14:58:49