示例：shell循环控制for、while语句

1.9 * 9 乘法表，for列表循环，for循环(c语言风格)， while循环
可选单层循环

#! /bin/bash

echo "==================for i in list==================="
for i in `seq 9`
do
    for j in `seq $i`
    do
        echo -n "$i*$j=$[i*j] "
    done
    echo
done

echo "==================for(())==================="


for((i=1,j=1;i<=9;j++))
do
    echo  -n  "$i*$j=$[i*j] "

    if [ $i == $j ];then
        echo -e '\n'
        let j=0
        let i=$i+1
    fi
done

echo "==================while==================="

let i=1;
while ((i<=9))
do
    let j=1;
    while (($j<=$i))
    do
        echo -ne "$i"*"$j=$[i*j]\t"
        let j++;
    done
echo ""
let i++;
done

2.使用for循环创建30个用户: test01~test30, 并设置密码为test01 123456~test30 123456

for i in `seq -f '%02g' 1 30`
do

    if id -u $i &> /dev/null;then
        echo test$i is exist!
        continue
    fi
        useradd test$i
        echo "test'$i'123456" | passwd --stdin test$i &> /dev/null

done

3.使用循环去判断网段内的IP(1~254)，本机除外，可以ping通的使用 ssh远程登录

for i in `seq 1 254`
do
   if [ $i -eq 135 ];then
        continue
   else 
        ping -c 2 -w 1 192.168.10.$i &> /dev/null
        if [ $? -eq 0 ];then
            ssh 192.168.10.$i
        fi
    fi
done

4.使用$@和$*作为for循环后的列表，并体现出区别

[root@servera bash]# bash @and\*.sh this is a example
echo "============$ @================"
for i in "$@"
do
    echo $i
done

echo "============$ *================"
for i in "$*"
do
    echo $*
done

[root@servera bash]# bash @and*.sh  this is a example
============$ @================
this
is
a
example
============$ *================
this is a example
[root@servera bash]#

5.使用循环去读取文件内容并输出: 3中方式(1.exec+while循环 2.管道符+while循环 3.重定向+while)

[root@servera bash]# echo data{1..3} > file.txt
echo "============= methon 1:exec+while ================"

exec < file.txt
while read a
do
    echo $a
done


echo "============= methon 2: | +while ================"
cat file.txt | while read line
do
    echo $line
done


echo "============= methon 3: < +while ================"
while read line
do
    echo $line
done < file.txt

[root@servera bash]# bash while_read.sh 
============= methon 1:exec+while ================
data1 data2 data3
============= methon 2: | +while ================
data1 data2 data3
============= methon 3: < +while ================
data1 data2 data3