Open Linux De Morgan Law with primitive force

De Morgan Law Let learning Liunx's small partners around the headache, now I use the force of the primitive to straighten out this law for everyone.

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As can be seen from the picture,

A=4+3

B=3+2

Non-a=2+1

Non-b=4+1

A and b means that both A and B are in place, A and b are colored block 3, so the color block 3 represents a and B

At the same time, we look at A=4+3, b=3+2, and we can infer that The result of the operation is the number of repetitions in the two arithmetic formula.

A and b=3

A or B is either a part of a or a part of B, so the color block 2,3,4 and represents the range of a or B. Looking at a=4+3,b=3+2, we can infer that the result of the operation is that all the numbers in the two arithmetic are added, and the repeated numbers are added only once.

A or b=2+3+4

A non-color block is the sum of all the other color blocks in addition to this color block. A non-n color block is the sum of other color blocks except for the n-color blocks.

Cases:

Non-3=1+2+4

As a result, we can perform the following operations

(not a) or (not b) = (2+1) or (4+1) =1+2+4

Non (A and B) = Non (4+3 and 3+2) = Non (3) =1+2+4

(Not a) and (not B) = (2+1) and (4+1) =1

Non (A or B) = Non (4+3 or 3+2) = Non (4+3+2) =1

We can draw the following conclusions:

(not a) or (not B) = Non (A and B)

(Non-a) and (not B) = Non (A or B)

Let's do the following exercises:

1. Chmod-rw/tmp/file1, write the script/root/bin/per.sh to determine if the current user is unreadable to the/tmp/fiile1 file and is not writable

   Method One:

   
   

[email protected] bin]# cat per.sh

#!/bin/bash

[!-r/tmp/file1-a!-w/tmp/file1] && echo "You can ' t read and write/tmp/file1" | | echo "You can read or write/tmp/file1"

Method Two:

[email protected] bin]# cat per2.sh

#!/bin/bash

! [-r/tmp/file1-o-w/tmp/file1] && echo "You can ' t read and write/tmp/file1" | | echo "You can read or write/tmp/file1"

The red mark is a different place in two statements, but the function is the same.

This article is from the "zebra930" blog, make sure to keep this source http://zebra930.blog.51cto.com/11736340/1837433

Open Linux De Morgan Law with primitive force