An array of bash script programming and random variables

Variable: The memory space used to store the value of existence; The feature is that only one value can be stored in a variable.

Array: a contiguous memory space capable of accommodating multiple array elements, including two types: 1. Sparse Array (bash is a sparse array): The element numbers in the array can be no order; 2. Dense arrays: Elements in an array must be ordered in sequential numbers.

Array elements: Any storage unit in the array that holds the data, which acts as a variable;

There are two types of identity of an element: The index array ID: All array elements are numbered by numbers, using the numeric numbering method;

Usually numeric numbers start from zero, i.e.: 0,1,2 ...

Associative array ID: All array elements can be identified by name or string, (it is possible to support associative arrays in versions above bash4.0 )

Declaration and definition of an array: Declare and define an array with the DECLARE command, directly using variable assignments, or defining array elements separately.

1.declare command:

Common options:

-A: Declares an indexed array, declaring the variable name after it as an indexed array, if supported (the version above bash4.0 is possible);

-A: Declares an associative array, declaring the variable name after it as an associative array, if supported (the version above bash4.0 is possible);

Example:

To define a dense array:

Declare-a names= ("Zhang" "Wang" "Liu" "li")

To define a sparse array:

Declare-a names2= ([0]= ' Zhangsan ' [2]= ' cl ' [3]= ' Mayun ')

2. How to assign values directly using variables:

Define a dense array of indexes:

Array_name= ("value1" "value2" "value3" ...)

To define a sparse index array:

Array_name= ([0]= "value1" [1]= "value2" [2] "value3" ...)

To define an associative array:

Array_name= ([index_name1]= "value1" [index_name3]= "value2" [index_name3]= "Value3" ...)

3. Define the array elements separately:

array_name[0]= ' value1 '

array_name[1]= ' value2 '

...

Array_name[n-1]= ' Value (N) '

Example:

[Email protected] ~]# student_info[0]= ' Xiaoma '

[[email protected] ~]# student_info[1]= ' 22 '

[Email protected] ~]# student_info[2]= ' xxxxxxxxxxxx '

[[email protected] ~]# echo ${student_info[1]}

22

How to reference array elements:

${array_name[index]}

Note: If you do not give a specific index number when referencing an array element, the default number is 0, which displays the value of the first array element;

Refer to all elements in the entire array:

${array_name[*]} or ${array_name[@]}

Index number of all elements referencing the entire array:

${! Array_name[*]} or ${! Array_name[@]}

To view the number of elements in an array (array length):

${#ARRAY_NAME [*]} or ${#ARRAY_NAME [@]}

Whole Group of slices:

${#ARRAY_NAME [*]:offset}

Displays the element that contains the position of the offset value and all subsequent elements thereof;

${#ARRAY_NAME [*]:offset:number}

Displays the value of the element that contains the position of the offset value and its number elements;

Undo Array:

Unset Array_Name

The elements in the array are revoked together and are invalidated;

Random variable:

Random number variable: The random number taken out is an integer value between 0-32767;

Taking random numbers from the entropy pool;

Entropy Pool:

/dev/random

Two times the time interval of hitting the keyboard;

Two time interval of IO;

/dev/urandom (pseudo-entropy pool)

Calculate the random number by using the application;

About taking random numbers, we can't always take random numbers in random, we can't get the values we've already got, so we can use a variable to define a random number: for example, var100= $RANDOM, so we can get the original repetition through Echo $VAR 100来. of random values.

An array of bash script programming and random variables