Shell script programming Array _linux Shell

An array is a set of elements of the same data type arranged in a certain order, that is, a variable of the same type is named with a name and then numbered to distinguish their set of variables, which is called an array name, and the number is called subscript. The variables that make up an array are called elements of an array. Arrays are in the program design, in order to deal with the convenience of the same type of a number of variables in order to organize a form.

One, the representation of the array

1, subscript array

Subscript must be an integer, format: array name [subscript], subscript default starting from 0.
The shell supports sparse arrays, and subscript integers do not need to be contiguous.
How to declare: DECLARE-A array name

2. Associative array

Associative arrays can use arbitrary strings as subscripts (not necessarily integers) to access array elements. Bash4.0 begins to support associative arrays.
Format: array name [arbitrary string]
Declaration by: declare-a Associative array
In addition, the shell supports only one-dimensional arrays and does not support multidimensional arrays.

Second, the assignment of the array

Three, array of access

Access to an array of elements is achieved by manipulating the syntax.

The syntax format has the following types:

Length of array:

${#ARRAY [*]}: Number of elements displayed;
${#ARRAY [@]}: Displays the number of elements;
${#ARRAY [#]}: Number of characters of the # element;
${#ARRAY}: Number of characters in the No. 0 element;

Elements of an array:

${array[*]}: Displays all element contents;
${array[@]}: Displays all element contents;
${array[#]}: Displays the # element;
${array}: Displays the No. 0 element;

The key value of the array:

$[! Array[*]}: Displays all the key values;
$[! array[@]}: Displays all the key values.

Example: Write a script that generates 10 random numbers, saves them to an array, and then displays the elements that are labeled even after the array:

Iv. Select elements from the array

If you want to take a few elements out of an array, it's more cumbersome to use the subscript to find each one, and you can use the Offset element feature of the array to simplify the operation.

Syntax format:

${array[@]:offset:number}
Offset: number of offsets;
Number: Amount of elements removed;

Instance: There are 6 elements in the array off_array, assuming we want to take the three values from March to May:

V. Array replication

$@: Each parameter is a separate string that is recommended for use;
$*: All elements as a string.

Instance: Copies an array of an even-numbered element into the new array:

Six, remove elements from the array

Format: unset array name [subscript]

Vii. Comprehensive Examples

Generates 10 random numbers and sorts the 10 random numbers.