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Tags: #linux #macos

Arrays

Arrays can be indexed either by numeric values (from zero) or by arbitrary strings (as an associative array/hash map). These are only supported in Bash 4.x and newer, which limits their use on MacOS' stock Bash which is frozen in time at 3.2.57 (as of 2022/12/07 on 13.0.1).

Declaring arrays is done via the declare command and requires choosing whether an array or an associative array is needed:

# ARRAY is indexed by integer values, starting at 0.
declare -a ARRAY

# ASSOCIATIVE_ARRAY is indexed by strings.
declare -A ASSOCIATIVE_ARRAY

Declaring Variables

Declaring variables prior to their first use is done via the declare command.

If a variable is defined in a function it will have local scope unless specified with a global scope via -g:

function do_something()
{
    # this is only accessible within do_something().
    declare LOCAL_VARIABLE

    # this will be accessible once do_something() returns.
    declare -g GLOBAL_VARIABLE
}