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This article shows you how to understand the logic and (&) in Bash. The content is concise and easy to understand. It will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

In Bash, you can use & as the AND (logical sum) operator.

Some people may think that the meaning of the two articles is similar, but it is not. Although the first article discussed how to use & at the end of the command to run the command in the background, and then dissected process management, the second article saw & as a way to reference file descriptors, which let us know. When used in combination, you can direct input or output somewhere else.

But we haven't touched the & which is used as an AND operator. So, let's take a look.

& is a bitwise operator

If you are familiar with binary number manipulation, you must have heard of AND and OR. These are bitwise operations that operate on the bits of a binary number. In Bash, use & as the AND operator and | as the OR operator:

AND:

0 & 0 = 00 & 1 = 01 & 0 = 01 & 1 = 1

OR:

0 | 0 = 00 | 1 = 11 | 0 = 11 | 1 = 1

You can AND any two numbers and use echo to output the results:

$echo $((2 & 3)) # 00000010 AND 00000011 = 000000102$ echo $((120 & 97)) # 01111000 AND 01100001 = 0110000096

The same is true of OR (|):

$echo $((2 | 3)) # 00000010 OR 00000011 = 000000113$ echo $((120 | 97)) # 01111000 OR 01100001 = 01111001121

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Use ((...)) to tell Bash that the content between the parentheses is some kind of arithmetic or logical operation. ((2 + 2)), ((5% 2)) (% is the modularization operator) and ((5% 2) + 1) (equal to 3) all work.

Like a variable, use $to extract the value so that you can use it.

Spaces have no effect: (2-3) is equivalent to (2-3) and (2-3).

Bash can only operate on integers. Try doing this: ((5 / 2)), you will get 2; or this ((2.5 & 7)), but you will get an error. Then, using anything but integers in bitwise operations (which is what we're talking about now) is usually something you shouldn't do.

Tip: if you want to see what decimal numbers look like in binary, you can use bc, a command-line calculator pre-installed with most Linux distributions. For example:

Bc

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