Shell Foundation--Numerical calculation of variables

Numerical Calculation of variables

1.$ ((expression))

(1). Experiment 1

[Email protected] ~_~ day4]# 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] ~_~ day4]# sh test.sh

A-b=4

A+b=8

A*b=12

A/b=3

A%b=0

a**b=36

(2). Experiment 2

[Email protected] ~_~ day4]# cat test2.sh

#!/bin/bash

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

[[email protected] ~_~ day4]# sh test2.sh 1 + 2

3

Note: "1 + 2" has a space and, if none, it is only passed to $

2. $[expression]

[Email protected] ~_~ day4]# Echo $[3+4]

7

3.let Assignment Expression

Equivalence with (()), but the latter is highly efficient

[Email protected] ~_~ day4]# i=10

[Email protected] ~_~ day4]# let i=i+1

[Email protected] ~_~ day4]# echo $i

11

4.expr-expression

Note: Operators and calculated values have spaces around them

(1). arithmetic

[Email protected] ~_~ day4]# cat expr.sh

#!/bin/bash

A=$1

B=$2

echo "a*b= ' expr $a + $b '"

echo "a-b= ' expr $a \* $b '"

[[email protected] ~_~ day4]# sh expr.sh 2 3

A*b=5

A-b=6

(2). determine file extension name

Used in: Ssh-copy-id file; (VIM ' which Ssh-copy-id ')

Usage:

[Email protected] ~_~ ~]# cat exprfile.sh

#!/bin/bash

If expr "$": ". *\.pub"; then

echo "is. pub file"

Else

echo "is not *.pub file"

Fi

[Email protected] ~_~ ~]# sh exprfile.sh test.pub

8

Is. pub file

[Email protected] ~_~ ~]# sh exprfile.sh test.pu

0

is not *.pub file

(3). determines whether a number is an integer

[Email protected] ~_~ day4]# cat isinteger.sh

#!/bin/bash

Expr + 1 &>/dev/null

If [$?-eq 0]

Then

echo "is Integer"

Else

echo "is not a Integer"

Fi

[[email protected] ~_~ day4]# sh isinteger.sh 3.9

is not a Integer

[[email protected] ~_~ day4]# sh isinteger.sh 3

Is Integer

(4). Calculating string Lengths

[[email protected] ~_~ day4]# echo ' expr length ' Hello '

5

There are other uses to view man expr

5.BC command

A calculator, installed with Yum; direct BC into the calculator; Supports floating point calculation.

(1). Interactive Environment

[Email protected] ~_~ day4]# BC

BC 1.06.95

Copyright 1991-1994, 1997, 1998, 2004, 2006 Free Software Foundation, Inc.

This is the free software with absolutely NO WARRANTY.

For details type ' warranty '.

2*3

6

3+7+5

15

3.4+5.6

9.0

(2). Add pipe character

[Email protected] ~_~ day4]# echo "3+5" |BC

8

(3). through Scale Specifying calculation Precision

[Email protected] ~_~ day4]# var=3.14

[Email protected] ~_~ day4]# var= ' echo ' scale=2; $var "|BC"

[Email protected] ~_~ day4]# echo $var

9.42

6.awk Command for calculation

Supports floating-point operations with log, sqr, cos, sin, and more

[[email protected] ~_~ day4]# var= ' echo ' $var ' |awk ' {printf ("%g", Sin ($)} "

[Email protected] ~_~ day4]# echo $var

0.841471

[[email protected] ~_~ day4]# var= ' echo ' $var 2 "|awk ' {printf ("%g ", cos ($1/$2))} '

[Email protected] ~_~ day4]# echo $var

0.97922

Shell Foundation--Numerical calculation of variables