linux下运算的几种方法

1.expr
　　1.1 最简单的用法

yan@yan:~$ expr 4 \* 5
20
yan@yan:~$ 

　　1.2 bash脚本对于expr

yan@yan:~$ cat expr1.sh 
#!/bin/bash

PATH=/home/yan/bin:/home/yan/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
export PATH

var1=100
var2=200

var3=$(expr $var2 / $var1)

echo "var3=$var3"
yan@yan:~$

yan@yan:~$ chmod 755 expr1.sh 
yan@yan:~$ ./expr1.sh 
var3=2
yan@yan:~$

2.方括号
　　2.1 最简单的用法

yan@yan:~$ echo "$[3+2]"
5
yan@yan:~$

　　2.2 bash对于脚本[]

yan@yan:~/leran/shell$ cat test1.sh 
#!/bin/bash

PATH=/home/yan/bin:/home/yan/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
export PATH

var1=100
var2=200

var3=$[$var2 / $var1]

echo "$var3"


yan@yan:~/leran/shell$ chmod 755 test1.sh 
yan@yan:~/leran/shell$ ./test1.sh 
2
yan@yan:~/leran/shell$

3.bc
　　3.1 最简单的用法

yan@yan:~/leran/shell$ 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'. 
3+2-5
0
quit
yan@yan:~/leran/shell$ 

　　其中:bc进入软件，quit退出软件

　　3.2 bash对于bc

yan@yan:~/leran/shell$ cat bc.sh 
#!/bin/bash

PATH=/home/yan/bin:/home/yan/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
export PATH

var1=200
var2=199
var3=$(echo "scale=5;$var1/$var2" | bc)
echo $var3
yan@yan:~/leran/shell$ chmod 755 bc.sh 
yan@yan:~/leran/shell$ ./bc.sh 
1.00502
yan@yan:~/leran/shell$