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Array concept

According to the production requirements, the data with some common characteristics are organized into a set to facilitate traversal, query and management, the array is a collection of variables, and the array in shell is equivalent to the list and dictionary of Python.

Ordinary array

1. The index number is a number, and the default starting index number is 02. This is equivalent to listing 3 in Python. There is no need to declare, just use

Associative array

1. The index format can be customized, and the associative array data is a collection of key values such as key and Value. Equivalent to a dictionary in python. 3. Must be declared first.

Sparse array:

The discontinuity of index numbers becomes a sparse array.

Array declaration:

Normal array: declare-an ARRAY_NAME

Associative array: declare-An ARRAY_NAME

View the data sets defined in the system declare-a

Array assignment

Assign only one element at a time

Assign all elements at once

Only assign values to specified elements

Interactive array

Data element reference

Reference array elements: ${ARRAY_ name [index]} reference array all elements ${ARRAY_NAME [*]} ${ARRAY_NAME [@]} length of data ${# ARRAY_NAME [*]} ${# ARRAY_NAME [@]} Delete elements in the array: cause the sparse format unset ARRAY [INDEX] to delete the entire array unset ARRAY

Example:

Array data processing

Syntax: ${ARRAY [@]: offset:number} n is the start and end position, m is the intercept length

Memory ideas:

Offset: the start offset of the element string from left to right is numbered 0, and the offset from right to element string is numbered-1

Offset: the element string offset number corresponds to the starting position in the Python string slice

When offset is positive, it is intercepted from left to right; if it is negative, it is intercepted from right to left.

Number: the length of the element string to be intercepted corresponds to the end position in the Python string slice.

When number is positive, it represents the intercept length, if it is negative, it represents the end position. When number is the end position, the interception does not include the m-bit.

Note: when using negative interception, negative numbers must be separated by a space from a colon.

When the instance 1:offset is positive, truncate from left to right: ${ARRAY [@]: N m}, n is the starting and ending position, m is the truncated length

From left to right, intercept the starting position is n, take m characters.

If the intercept length m is not specified, the nth bit is intercepted to the end of the element string

Example 2:

If offset is negative, truncate it from right to left. If it is negative, you must add a space ${ARRAY [@]:-n:-m} or ${ARRAY [*]:-n ARRAY m} after the colon.

${ARRAY [@]:-n m}: from right to left, the element string offset is numbered from right to left as-1 to-n, the starting position of the intercept is-n, and m characters are taken. ${ARRAY [@]:-n:-m}: from right to left, the element string offset is numbered from right to left as-1 to-n, the start position of the intercept is-n, and the end position is-m characters.

It is important to keep in mind that once an array is defined, you can only append elements to one by one in the array, or modify element values, and cannot add elements in batches. Batch assignment batch is array initialization.

ARRAY [${# ARRAY []}] = the number of value elements plus 1 to assign

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