Shulou(Shulou.com)06/01 Report--

First, use bash script programming to realize arithmetic operation.

1)

+, -: add operation

*, /

%: modular operation, take remainder

* * | ^

2) enhanced arithmetic symbols:

+ =: let B=B+2-- > let Barrier 2

-=: let B=B-2-- > let Bmuri 2

* =: let B=B*2-- > let Barrier 2

/ =: let B=B/2-- > let Bplink 2

% =: let B=B%2-- > let B% room2

3) Special enhanced arithmetic operations:

Let B=B+1-- > let Barrier 1-- > let Barrier +

Let B=B-1-- > let Bmuri 1-- > let Bmuri--

Bounded variables: first assign the value of B to other variables, and then itself + 1

+ B: do your own + 1 calculation first, and then assign the value of B to other variables

Method of arithmetic operation:

1.let VAR= arithmetic expression

The arithmetic expression is operated in advance, and the result of the operation is saved to the variable VAR

2. VARTED $[arithmetic expression]

If there is a variable reference in an arithmetic expression, you can use a $reference or omit it

SUM=$ [Cobb] is equivalent to SUM=$ [$Cobb]

3.VARTED $((arithmetic expression))

If there is a variable reference in an arithmetic expression, you can use a $reference or omit it

4.expr ARGU1 ARGU2 ARGU3

ARGU1 and ARGU3 must be numeric

ARGU2 must be an operation symbol

5.echo "is an expression" | bc

Note: the * sign, in some cases, needs to be escaped

Variables: containers in which data are stored

Weak variables: weakly typed variables, character type (default), numeric type (excluding floating point type)

2. Conditional test commands:

Test EXPRESSION

Shell built-in command

[EXPRESSION]

External command [external command]

`EXPRESSION'

Internal keywords of bash

/ Note: this kind of command generally has no execution result, but only returns the value of execution status. Test generally has two formats. When using square brackets, you should pay attention to adding spaces on both sides of the condition:

There are three types of test expressions for test test commands:

1. Numeric testing: Binocular operator

-eq: whether the two values tested are equal, true or false

-ne: whether the two values tested are not equal, true or false

-gt: whether the value on the left is larger than that on the right, whether it is true, and not greater than if it is false.

-lt: whether the left value is smaller than the right value, less than true, and not less than false

-ge: whether the left value is greater than or equal to the right value, greater than or equal to true, and less than is false

-le: whether the two values tested are less than or equal to the right, less than or equal to true, and greater than false

Example: whether the size of ~ / aaa is less than 1000 bytes

[root@mylab1 ~] # [$(ls-l aaa | awk'{print $5}')-lt 1000] & & echo OK | | echo "bu OK"

OK

two。 String test

1) Binocular operator:

= = | =: whether the two strings tested are the same, the same is true, and the difference is false

! =: whether the two strings tested are different, the difference is true, and the same is false

>: the corresponding binary values of the two strings tested in the ASCII code table, whether the left is greater than the right, greater than true, less than false

And

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