The usage of shell array

Variable: the memory space that stores a single element:

Array (multiple contiguous memory spaces): contiguous memory space that stores multiple elements:

Array name:

Index: numbering starts at 0 and belongs to numeric index

Note: indexes can also support custom formats, not just numeric formats:

The array of bash supports sparse format

Reference elements in the array: ${ARRAY_ name [index]}

Declare an array:

Declare-an ARRAY_NAME

Declare-An ARRAY_NAME: associative array: kv

Assignment of array elements:

(1) assign only one element at a time:

ARRAY_ name [index] = VALUE

# weekdays [0] = "Sunday"

# weekdays [4] = "Thursday"

(2) assign all elements at once:

ARRAY_NAME= ("VAL1", "VAL2", "VAL3",...)

(3) only specific elements are assigned:

ARRAY_NAME= ([0] = "VAL1" [3] = "VAL2"...)

(4) read-an ARRAY

Reference an element in the array:

${ARRAY_ name [index]}

Note: omitting [INDEX] indicates referencing the element with subscript 0

Show all elements in the array:

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

Count the length of the array (the number of elements in the array):

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

Reference elements in an array:

Fetch all the elements in the array in turn: ${ARRAY [@]} or ${ARRAY [*]}

Array slices:

Take out the element of specified length in the array: ${ARRAY [@]: offset:number}: also called array slice

Offset: the number of elements to skip

Number: the number of elements to be taken out

Example: # echo ${weekdays [@]: 1:2}

All elements after the offset is taken out: ${ARRAY [@]: offset}

# echo ${weekdays [@]: 1}

Append elements to the array:

ARRAY [${# ARRAY [*]}]

Delete an element from the array:

Unset ARRAY [INDEX]

Associative array:

Declare-An ARRAY_NAME

ARRAY_NAME= ([index_name] = 'val1' [index_name2='val2'...])