Array of shell script programming

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 the set of the variable is distinguished by a number, which is called the array name, and the number is called the subscript. The individual variables that make up the array are called elements of the array. An array is a form in which a number of variables of the same type are organized in an orderly manner in order to deal with them conveniently.

I. How arrays are represented

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.

Declaration method: Declare-a Array Name

2. Associative arrays

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 method: 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

1. Assign a value to one element at a time

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2. Assign values to all elements at once

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3, by index to assign value

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4. Command substitution Assignment

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5. User input

Using the read command to implement an interactive assignment, format: read-a array name

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Iii. Access to arrays

Access to the array elements is implemented by manipulating the syntax.

There are several syntax formats:

The length of the array:

${#ARRAY [*]}: Displays the number of elements;

${#ARRAY [@]}: Displays the number of elements;

${#ARRAY [#]}: Number of characters of the # element;

${#ARRAY}: The number of characters in the No. 0 element;

Elements of the array:

${array[*]}: Displays the contents of all elements;

${array[@]}: Displays the contents of all elements;

${array[#]}: Displays the first # elements;

${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, generate 10 random numbers, save to an array, and then display an array of elements labeled even:

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Iv. selecting elements from an array

If you want to remove a few elements from an array, it is cumbersome to use the subscript to find each other, and you can use the Offset element feature of the array to simplify the operation.

Syntax format:

${array[@]:offset:number}

Offset: The number of displaced elements;

Number: How many elements are removed;

Example: There are 6 elements in the array off_array, assuming we want to take March to May of these three values:

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If you want to remove all elements after the offset, omit the nubmer, such as:

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V. Array replication

[Email protected]: Each parameter is a separate string, recommended to use;

$*: All elements as a string.

Example: Copying an even-numbered element in an array to a new array:

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Vi. removing elements from an array

Format: unset array name [subscript]

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Vii. Comprehensive Examples

Generates 10 random numbers and sorts the 10 random numbers.

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Array of shell script programming