[Shell programming] Examples of numerical calculation methods in shell programming

Shell programming often involves the calculation of numerical values, and sometimes it is easy to forget or confuse the scenarios for these calculation commands, which is a summary of commonly used calculations. The main include let, BC, expr, (()) and so on.

1. Let

using the format: let expression, the expression must be a complete expression, that is, both sides of the equal sign. Can only be assigned, does not support floating-point arithmetic, direct output is not supported

$ var=$ let var+ =2 #var =, Middle cannot have spaces  $ let var=var+2 # Var=$ let var*=2 #var = $letvar/=2 # var=14 

Unable to calculate floating point number, error

$ var=2.5$ let var+ =1-bash:let:2.5: syntax error: Invalid arithmetic operator (error symbol is ". 5")

2. BC

Commonly used, support floating-point arithmetic

Echo " up"| BC #2Echo "1.5+1.5"| BC #3.0Echo "3-1.2"| BC #1.8Echo "1.5*1.5"| BC #2.2Echo "10/3"| BC #3Echo "SCALE=2;10/3"| BC #3.33

Do you see a difference in the accuracy of multipliers and divisor? Set other parameters under test

Echo "1.5*1.33333"| BC #1.99999Echo "1.5111111111111111111111*1.33333"| BC #2.0148097777777777777777Echo "4/5"| BC #0Echo " the"| BC #0Echo "6/5"| BC #1

The accuracy of the multiplication output is consistent with the longest progress of the phase multiplier. Integer division results are rounded. Of course, it can be assigned a value

var=$ (echo"|bc") #var =2

3. Expr

floating-point arithmetic is not supported, note the numbers and spaces in the calculation characters

Expr 1+1#2Expr 1-1#0Expr 1\*1#1Notethe number is preceded by a \, otherwise errorExpr 1/1#1Expr 1+1 #1 +1, inconsistent with expectationsExpr 1.0+1 #输出语法错误var=$(Expr 1+1) #var =2var2=$(Expr${var} +2) #var2 =4

4, $ (())

Floating-point arithmetic is not supported, the window is not supported to execute $ (()) directly,

var=$ (()) #1 whether there are spaces in the middle of the +1 operator without affecting the calculation
v1=10
V2=15
var=$ ((V1+V2))
var=$ (($v 1+ $v 2))
a=$ ((1 + 1.0)) #提示语法错误

It can be found that the variable with no $ value symbol in $ (()) does not affect the calculation.

5. Awk

Awk combined with the use of print can be a good variety of complete numerical calculations, including floating point number and precision control.

awk ' begin{printf 1.0/2.0} ' #0.5  awk'begin{printf ' 5.2f% ", 10/3}' #3.$ var1=Ten $ var2=3awk'begin{printf "%5.2f\n", v1/v2}  ' #3.33

Finally, let's look at an example, output the value of

#!/bin/Bashi=1MAX=5 while [${i}-lt ${max}];  Do   "${i}\n" I =$ (($i + 1)) done     

Output results

1 2 3 4

[Shell programming] Examples of numerical calculation methods in shell programming