10.Shell operator

Bash supports many operators, including arithmetic operators, relational operators, Boolean operators, string operators, and file test operators.

Native Bash does not support simple math operations, but can be implemented with other commands, such as awk and expr,expr, which are most commonly used.

expr is an expression evaluation tool that uses it to perform evaluation operations on expressions.

For example, two numbers are added:

#!/bin/bash

caoliu= ' Expr 2 + 2 '

Echo $caoliu

Two points Note:

• There are spaces between the expression and the operator, such as the 2 + 2, which is different from most of the programming languages we are familiar with.

• The complete expression is to be contained, note that this character is not a common single quote, below the ESC key.

Arithmetic operators

Let's take a look at an example that uses arithmetic operators:

#!/bin/sha=10b=20val= ' expr $a + $b ' echo ' A + B: $val ' val= ' expr $a-$b ' echo ' A-B: $val ' val= ' expr $a \* $b ' echo ' A * : $val "val=" expr $b/$a ' echo ' b/a: $val "val=" expr $b% $a ' echo ' B% A: $val "if [$a = = $b]then echo" a equals B "Fiif [$ A! = $b]then echo "A not equal to B" fi

Results:

A + b:30

A-B: 10

A * b:200

B/A: 2

B% a:0

A is not equal to B

Attention:

• Multiplication sign (*) must be added in front of the backslash (\) to achieve the multiplication operation;

• If...then...fi is a conditional statement that will be explained later.

This article is from the "8159085" blog, please be sure to keep this source http://8169085.blog.51cto.com/8159085/1793549

10.Shell operator