6、 Symbols and commands for numerical calculation of variables

1. Common arithmetic operators

Symbol	explain
+、-	plus 、 minus sign
*、/、%	Multiplication 、 Touch method 、 Remainder
**	Nether operation
++、--	Increase or decrease 、 Reduce
!、&&、||	Logic is not （ Take the opposite ）、 Logic and （and）、 Logic or （or）
<、<=、>、>=	Comparative symbols （ Less than 、 Greater than ）
==、!=、=	Comparative symbols （ equal 、 It's not equal 、 amount to ）
<<、>>	Shift left 、 Shift right
~、|、&、^	According to the not 、 Exclusive or 、 And 、 or
=、+=、-=、*=、/+、%=	The assignment operation （a+=1 amount to a=a+1）

2. Common arithmetic operation commands

Symbol	explain
(())	Common operators for integer operations , It's very efficient
let	For integer operations , Be similar to "(())"
expr	Can be used for integer operations , There are many other features
bc	linux Calculator program under , Suitable for integer and decimal
$[]	For integer operations
awk	awk Can be used for integers , It can also be used for decimal operations
declare	Define variable values and properties ,-i Parameters can be used to define shaping variables , Do calculations

Two 、 Calculation practice

1. Double brackets

1) Routine usage

Symbol	explain
((i=i++))	Operation after assignment
((i=++i))	Evaluate first and then assign
i=$((i+1))	Assign values to variables after operation i
((a>7&&b<5))	Do a comparison operation , You can also make conditional judgments
echo $((2+1))	The result of the world output expression

++、-- Memory method of operation ： i=i++ It means right first i assignment , And then do the self addition operation , That is, the actual i Value than output i Large value i=++i Indicates that the self addition operation is performed first , In the face of i assignment , That is, the actual i And the output of i equally

2)i++ and ++i test

• i=6;echo $((i++));echo $i

6
7

• i=6;echo $((++i));echo $i

7
7

2. Other calculation commands

1) let Assignment expression

let i=i+2 Equate to ((i=i+2))

2) bc Calculation command

bc yes linux Under the computer , The matching pipe is often used for calculation , You can perform decimal operations

echo "1+9"|bc
i=5;i=`echo $i+6|bc`

3) awk Do arithmetic

Decimals can be made 、 The operation of integers , useful echo "7.7 9.8"|awk '{print ($1+$2),($1*$2)}'

17.5 75.46

4) $[] Do calculations

echo $[4+2] $[4*2] $[4**2]

6 8 16

3、 ... and 、 Case study

1. Achieve output 1+2+3..+10=55 Calculation and output of

• Method 1：

echo `seq -s "+" 10`=`seq -s + 10|bc`

1+2+3+4+5+6+7+8+9+10=55

• Method 2：

echo `echo {1..10}|tr " " "+"`=`echo {1..10}|tr " " "+"|bc`

1+2+3+4+5+6+7+8+9+10=55

• Method 3：expr

echo `seq -s + 10`=`seq -s " + " 10|xargs expr`

1+2+3+4+5+6+7+8+9+10=55

• Method 4：(())

echo `seq -s + 10`=$((`seq -s + 10`))  

1+2+3+4+5+6+7+8+9+10=55

2.read Command to read parameters

1) read Command basis

• grammar ：read [ Parameters ] [ Variable name ] -p Set the prompt message -t Set the input waiting time （ second ） read -t 10 -p "input tow num:" a b

input tow num:1 2 Set up 10 Second timeout , The prompt is **

2) Calculation script Demo

• cat /server/scripts/t.sh

#!/bin/bash
read -p "num1:" a
read -p "num2:" 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))"

After allowing scripts , Prompt the function of entering two strings respectively

3) The script adds a judgment integer statement

• cat /server/scripts/t.sh

#!/bin/bash
#no.1
read -p "num1:" a
expr $a + 0 &>/dev/null
[ $? -ne 0 ] && {
    echo "pls int"
    exit 1
}
#no.2
read -p "num2:" b
expr $b + 0 &>/dev/null
[ $? -ne 0 ] && {
    echo "pls int"
    exit 2
}
#no.3
echo "a-b=$(($a-$b))"
echo "a+b=$(($a+$b))"
echo "a*b=$(($a*$b))"
echo "a/b=$(($a/$b))"
echo "a**b=$(($a**$b))"

For each input string , Verify that it is an integer , If it is not an integer, prompt and exit , After both are integers , Then calculate