Shell变量案例
1. 把以下的字符串中长度小于5的打印出来

When find examines or prints information a file

方法一：  了解
[root@shell /scripts]# echo When find examines or prints information a file | xargs -n1 |awk '{if(length<5)print}'
When
find
or
a
file


方法二： 
[root@shell /scripts]# cat length.sh
#!/bin/bash
for i in When find examines or prints information a file
do
    [ ${#i} -lt 5 ] && echo $i
done
[root@shell /scripts]# sh length.sh
When
find
or
a
file

Shell变量运算

加减乘除 求余
num1  +  num2  
num1  -  num2
num1  *  num2
num1  /  num2
num1  %  num2

整数运算

expr
$(())  
$[]
let
只支持整数运算，不支持小数运算

expr    数值之间必须要有空格进行分开，当使用*乘的时候，需要对其进行转义使用，不能进行求方运算
[root@shell /scripts]# expr 1 + 1 
2
[root@shell /scripts]# num1=10
[root@shell /scripts]# num2=5
[root@shell /scripts]# expr $num1 + $num2
15
[root@shell /scripts]# expr $num1 - $num2
5
[root@shell /scripts]# expr $num1 * $num2
expr: syntax error
[root@shell /scripts]# expr $num1 \* $num2
50
[root@shell /scripts]# expr $num1 / $num2
2
[root@shell /scripts]# expr $num1 % $num2
0
[root@shell /scripts]# num1=11
[root@shell /scripts]# expr $num1 % $num2
1

$(())  没有严格格式要求，不能进行求方运算

[root@shell /scripts]# echo $(($num1+$num2))
16
[root@shell /scripts]# echo $(( $num1 + $num2 ))
16
[root@shell /scripts]# echo $(( $num1 - $num2 ))
6
[root@shell /scripts]# echo $(( $num1 * $num2 ))
55
[root@shell /scripts]# echo $(( $num1 / $num2 ))
2
[root@shell /scripts]# echo $(( $num1 % $num2 ))
1


$[]   没有严格格式要求，不能进行求方运算

[root@shell /scripts]# echo $[$num1+$num2]
16
[root@shell /scripts]# echo $[1+1]
2
[root@shell /scripts]# echo $[ $num1 - $num2 ]
6
[root@shell /scripts]# echo $[ $num1 * $num2 ]
55
[root@shell /scripts]# echo $[ $num1 / $num2 ]
2
[root@shell /scripts]# echo $[ $num1 % $num2 ]
1

let   计数

[root@shell /scripts]# a=10
[root@shell /scripts]# let a++
[root@shell /scripts]# let a++
[root@shell /scripts]# let a++
[root@shell /scripts]# echo $a
13
[root@shell /scripts]# let a--
[root@shell /scripts]# echo $a
12
[root@shell /scripts]# echo $a
12
[root@shell /scripts]# let a--
[root@shell /scripts]# echo $a
11

小数运算

bc  awk  python

bc

[root@shell /scripts]# yum install -y bc

[root@shell /scripts]# bc
bc 1.06.95
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'. 
1+1
2
3/2
1
^C
(interrupt) Exiting bc.
[root@shell /scripts]# echo 10 + 20 | bc
30
[root@shell /scripts]# echo $num1 + $num2 | bc
16
[root@shell /scripts]# echo $num1 / $num2 | bc
2
[root@shell /scripts]# echo "scale=2;$num1 / $num2" | bc
2.20
[root@shell /scripts]# echo "scale=1;$num1 / $num2" | bc
2.2
[root@shell /scripts]# echo "scale=5;$num1 / $num2" | bc
2.20000
[root@shell /scripts]# echo "$num1 ^ $num2" | bc        #求方运算
161051


awk  

[root@shell /scripts]# awk 'BEGIN{print 10 + 5}'
15
[root@shell /scripts]# awk 'BEGIN{print 10 - 5}'
5
[root@shell /scripts]# awk 'BEGIN{print 10 * 5}'
50
[root@shell /scripts]# awk 'BEGIN{print 10 / 5}'
2
[root@shell /scripts]# awk 'BEGIN{print 10 % 5}'
0
[root@shell /scripts]# awk 'BEGIN{print 10 ^ 5}'
100000
[root@shell /scripts]# awk 'BEGIN{print 11 ^ 5}'
161051
[root@shell /scripts]# awk 'BEGIN{print 11 / 5}'
2.2
[root@shell /scripts]# awk 'BEGIN{print 10 / 3}'
3.33333
[root@shell /scripts]# awk 'BEGIN{printf "%.3f\n",10/3}'
3.333
[root@shell /scripts]# awk 'BEGIN{printf "%.3f",10/3}'
3.333[root@shell /scripts]# 
[root@shell /scripts]# awk "BEGIN{print $num1/$num2}"
2.2

[root@shell /scripts]# awk -vnum1=10 -vnum2=5  'BEGIN{print num1/num2}'
2

-v  #自定义内部变量

BEGIN  行处理前

python

[root@shell /scripts]# python
Python 2.7.5 (default, Oct 30 2018, 23:45:53) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-36)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 1+1
2
>>> 10^10
0
>>> 10/3
3
>>> 10.0/3
3.3333333333333335
>>> 
KeyboardInterrupt
>>> quit
Use quit() or Ctrl-D (i.e. EOF) to exit
>>> quit() 
[root@shell /scripts]# echo "print $num1 + $num2" | python
16
[root@shell /scripts]# echo "print $num1 - $num2" | python
6
[root@shell /scripts]# echo "print $num1 ^ $num2" | python
14
[root@shell /scripts]# echo "print $num1 / $num2" | python
2
[root@shell /scripts]# echo "print ${num1}.0 / $num2" | python
2.2

变量运算案例

1. ps aux命令下，求VSZ列的和

#第一种
[root@shell /scripts]# ps aux | awk 'NR>1{print $5}' | xargs  | tr ' ' '+' | bc
4672184

#第二种方法
[root@shell /scripts]# ps aux | awk 'NR>1{i+=$5}END{print i}'
4442724

#第三种方法
[root@shell /scripts]# cat for_vsz.sh
#!/bin/bash
he=0
for i in $(ps aux| awk 'NR>1{print $5}')
do
    he=$(expr $he + $i)
done
echo $he



2. 写个脚本，实现一个简单的计算器，实现加减乘除
[root@shell /scripts]# sh jsq.sh
请输入你要计算的第一个数字：10
请输入你要计算的第二个数字：10
10 + 10 = 20
10 - 10 = 0
10 * 10 = 100
10 / 10 = 1

[root@shell /scripts]# cat jsq.sh
#!/bin/bash
read -p "请输入你要计算的第一个数字：" num1
read -p "请输入你要计算的第二个数字：" num2
echo "$num1 + $num2 = $[ $num1 + $num2 ]"
echo "$num1 - $num2 = $[ $num1 - $num2 ]"
echo "$num1 * $num2 = $[ $num1 * $num2 ]"
echo "$num1 / $num2 = $(awk "BEGIN{print $num1 / $num2 }")"

Shell变量案例

需求描述：变量string="Bigdata process is Hadoop, Hadoop is open source project"，执行脚本后，打印输出string变量，并给出用户以下选项：
#需求
1)打印string长度
2)删除字符串中所有的Hadoop
3)替换第一个Hadoop为Linux
4)替换全部Hadoop为Linux
用户请输入数字1|2|3|4，可以执行对应项的功能。

#!/bin/bash
string="Bigdata process is Hadoop, Hadoop is open source project"
echo "语句为:$string"
echo -e "\033[44;37m 1)打印string长度\n2)删除字符串中所有的Hadoop\n3)替换第一个Hadoop为Linux\n4)替换全部Hadoop为Linux\n6)退出 \033[0m"
while :
do
read -p "请输入:[1|2|3|4|6]::" qq
if [ $qq -eq 1 ];then
    echo "${#string}"
elif [ $qq -eq 2 ];then
        echo "${string//Hadoop/}"
elif [ $qq -eq 3 ];then
    echo "${string/Hadoop/Linux}"
elif [ $qq -eq 4 ];then
       echo "${string//Hadoop/Linux}"
elif [ $qq -eq 6 ];then
    exit
else
    echo "输入错误"
fi
done