while list-1; do list-2; done

每2秒查看一下某个命令的执行结果
while true; do
    w
    sleep 2
done

while true; do uptime; sleep 2; done

######################## while 循环按行读取文件总结 ########################
exec < file.txt
sum=0
while read line; do
    cmd
done

cat file.txt | while read line; do
    cmd
done

while read line; do
    cmd
done < file


$ cat file.txt 
hello1
hello2
hello3
hello4
$ cat file.txt | while read line; do
    echo "$line 123456"
done

for name [ [ in [ word ... ] ] ; ] do list ; done
for (( expr1 ; expr2 ; expr3 )) ; do list ; done
select name [ in word ] ; do list ; done


for ((i=1; i<=3; i++)); do
    echo $i
done
for ((i=1; i<=3; i++)); do echo $i; done

for i in 5 4 3 2 1; do
    echo $i
done
for i in 5 4 3 2 1; do echo $i; done

for i in {1..5};               do echo $i; done
for i in {5..1};               do echo $i; done
for i in `seq 5`;              do echo $i; done
for i in `ls /tmp`;            do echo $i; done
for i in `cat /tmp/hello.txt`; do echo $i; done


简单实践: 批量给文件名增加 .conf 后缀
$ touch conf{1..8}
$ ls
conf1  conf2  conf3  conf4  conf5  conf6  conf7  conf8
$ for i in `ls`; do mv $i ${i}.conf; done
$ ls
conf1.conf  conf2.conf  conf3.conf  conf4.conf  conf5.conf  conf6.conf  conf7.conf  conf8.conf

break n
continue n
exit n
return n

for i in 5 4 3 2 1; do
    echo $i
    if [ $i -eq 3 ]; then
        break
    fi
done

for i in 5 4 3 2 1; do
    # echo $i
    if [ $i -eq 3 ]; then
        continue
    fi
    echo $i
done

for i in 5 4 3 2 1; do
    echo $i
    if [ $i -eq 3 ]; then
        exit
    fi
done

输出99乘法表
[root@as4k scripts]# cat mul99.sh 
#!/bin/bash
for ((x = 1; x <= 9; x = x + 1)); do
    for ((y = 1; y <= x; y = y + 1)); do
        printf "%dx%d=%d " $x $y $((x * y))
    done
    printf "\n"
done

写一个脚本实现判断192.168.1.0/24 网络里，当前在线的ip有哪些。
解答：
shell> cat tping.sh 
#!/bin/bash
for i in 172.16.1.{1..254}; do
{
    ping -c 2 $i &> /dev/null
    if [ $? -eq 0 ]; then
        echo $i is ok.
    fi
} &
done
wait

简单计算器-交互式
整数计算
[root@as4k scripts]# cat cal-read.sh 

#!/bin/bash
read -p 'Please input number1: ' n1
read -p 'Please input number2: ' n2

echo "for integer"
echo "$n1 + $n2 = $(( n1 + n2 ))"
echo "$n1 - $n2 = $(( n1 - n2 ))"
echo "$n1 * $n2 = $(( n1 * n2 ))"
echo "$n1 / $n2 = $(( n1 / n2 ))"


整数和小数计算
[root@as4k scripts]# cat cal-read.sh 
#!/bin/bash
read -p 'Please input number1: ' n1
read -p 'Please input number2: ' n2

echo "for integer and float"
add=`echo "$n1 $n2" | awk '{print ($1 + $2)}'`
subtract=`echo "$n1 $n2" | awk '{print ($1 - $2)}'`
multiply=`echo "$n1 $n2" | awk '{print ($1 * $2)}'`
divide=`echo "$n1 $n2" | awk '{print ($1 / $2)}'`
echo "$n1 + $n2 = $add"
echo "$n1 - $n2 = $subtract"
echo "$n1 * $n2 = $multiply"
echo "$n1 / $n2 = $divide"
# 效果
[root@as4k scripts]# sh cal-read.sh 
Please input number1: 2.3
Please input number2: 2.1
for integer and float
2.3 + 2.1 = 4.4
2.3 - 2.1 = 0.2
2.3 * 2.1 = 4.83
2.3 / 2.1 = 1.09524



简单计算器-传参式
[root@as4k scripts]# cat cal-read.sh 
#!/bin/bash
echo "for integer and float"
add=`echo "$1 $2" | awk '{print ($1 + $2)}'`
subtract=`echo "$1 $2" | awk '{print ($1 - $2)}'`
multiply=`echo "$1 $2" | awk '{print ($1 * $2)}'`
divide=`echo "$1 $2" | awk '{print ($1 / $2)}'`
echo "$1 + $2 = $add"
echo "$1 - $2 = $subtract"
echo "$1 * $2 = $multiply"
echo "$1 / $2 = $divide"
# 效果
[root@as4k scripts]# sh cal-read.sh 2.3 22
for integer and float
2.3 + 22 = 24.3
2.3 - 22 = -19.7
2.3 * 22 = 50.6
2.3 / 22 = 0.104545