Numerical calculation of shell-variables

The numerical computation of a variable is like a command.

(()), let, expr, BC, $[]

Here's a look at the operator of numeric calculations

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(()) This method is commonly used and efficient to perform integer-type calculations and does not support floating-point types.

[Email protected] ~]# ((a=1+2**3-4%3))

[Email protected] ~]# echo $a

8

[Email protected] ~]# b=$ ((1+2**3-4%3))

[Email protected] ~]# echo $b

8

[Email protected] ~]#

Where 2**3 is 2 of the 3-time Square

[[email protected] ~]# echo $ ((a++))

8

[Email protected] ~]# echo $a

9

[[email protected] ~]# echo $ ((a--))

9

[Email protected] ~]# echo $a

8

[[email protected] ~]# echo $ ((++a))

9

[Email protected] ~]# echo $a

9

[[email protected] ~]# echo $ ((--a))

8

[Email protected] ~]# echo $a

8

[Email protected] ~]#

As can be seen above, $ ((a++)) is the first output of a original value to add, and then we echo $a, is actually the output variable a after the value of the operation.

Memory method: Before the variable, the output variable value, the variable after the first place after the output variable value

The above are all integers, if there are decimal words will be an error, if you want to use the decimal Word can use the BC command

[email protected] ~]# cat test.sh

#!/bin/bash

A=6

b=2

echo "a-b=$ (($a-$b))"

echo "a-b=$ (($a + $b))"

echo "a-b=$ (($a * $b))"

echo "a-b=$ (($a/$b))"

echo "a-b=$ (($a * * $b))"

echo "a-b=$ (($a% $b))"

[Email protected] ~]# sh test.sh

A-b=4

A-b=8

A-b=12

A-b=3

a-b=36

A-b=0

If you want to implement the above operation by command-line arguments, you can modify the script to the following

#!/bin/bash

A=$1

B=$2

echo "a-b=$ (($a-$b))"

echo "a-b=$ (($a + $b))"

echo "a-b=$ (($a * $b))"

echo "a-b=$ (($a/$b))"

echo "a-b=$ (($a * * $b))"

echo "a-b=$ (($a% $b))"

Execute command

"Test.sh" 9L, 167C written

[[Email protected] ~]# SH test.sh 8 2

A-b=6

a-b=10

A-b=16

A-b=4

A-b=64

A-b=0

[[Email protected] ~]# SH test.sh 8 3

A-b=5

a-b=11

A-b=24

a-b=2

a-b=512

a-b=2

Now let's make a little calculator

[email protected] shell]# cat compute.sh

#!/bin/bash

echo $ (($1$2$3))

[Email protected] shell]# sh compute.sh 1+2

3

[Email protected] shell]#

Of course this is relatively simple, a lot of bugs we can look at other people write

http://chenhao6.blog.51cto.com/6228054/1232070

Some of the code is good to write, as follows

#!/bin/bash
echo "----------------------------------"
echo "| This is a simple integer calculator, author yuan|"
echo "----------------------------------"
Echo
While:
Do
Read-p "Please enter an integer:" Nu
Expr $nu + 0 &>/dev/null
If [$?-eq 0]
Then
echo "First number is $nu"
Break

Else
echo "The $nu you entered is not an integer, please re-enter"
Fi
Done

While:
Do
Read-p "Please enter two integers:" nu2
Expr $nu 2 + 0 &>/dev/null
If [$?-eq 0]
Then
echo "Second number is $NU2"
Break
Else
echo "The $nu2 you entered is not an integer, please re-enter"
Fi
Done
echo "------------------"
echo "| 1. Addition|"
echo "| 2. Subtraction | "
echo "| 3. Multiplication | "
echo "| 4. Division | "
echo "------------------"
Read-p "Please enter the algorithm you want to execute:" Me
Case $me in
"1")
sum= ' expr $nu + $nu 2 '
echo "$nu + $nu 2= $sum"
;;
"2")
jian= ' Expr $nu-$nu 2 '
echo "$nu-$nu 2= $jian"
;;
"3")
chen= ' expr $nu \* $nu 2 '
echo "$nu * $nu 2= $chen"
;;
"4")
chu= ' expr $nu/$nu 2 '
echo "$nu/$nu 2= $chu"
Esac

This article is from "Love Zhou Yu" blog, please be sure to keep this source http://izhouyu.blog.51cto.com/10318932/1889980

Numerical calculation of shell-variables