Bash Arrays
===========

Literal arrays
^^^^^^^^^^^^^^

.. code-block:: bash

    # literal array of four strings
    arx=( a b c d )

    # print the whole array, we can't just do $arx, because this is an Array!
    echo ${arx[@]}

    # Indexing an Array
    echo ${arx[1]} # b

    # get the length of the array
    len=${#arx[@]}
    # this also works, but will not quote internal array strings that might have the splitter
    len2=${#arx[*]}

    # last index of the array
    last_element=$(( len - 1 ))

    # Grab the last element of the array
    echo ${arx[$(( len - 1 ))]} # echo d
    # or
    echo ${arx[(( len - 1 ))]} # omit the internal $
    # or
    echo ${arx[$(( ${#arx[@]} - 1 ))]}

    # or even
    echo ${arx[(( {#arx[@]} - 1 ))]}


dynamically created Arrays
^^^^^^^^^^^^^^^^^^^^^^^^^^

.. code-block:: bash

    IFS=":"; path_tokens=( $PATH ); unset IFS

    # or

    path_tokens=( $(echo $PATH | tr ":" " ") )

    echo "PATH has ${#path_tokens[@]} tokens"

    echo "$PATH"

    len=${#path_tokens[@]}
    echo "last path is ${path_tokens[(( len - 1 ))]}"

    # or

    echo "last path is ${path_tokens[(( $len - 1 ))]}"

    # or

    echo "last path is ${path_tokens[(( ${#path_tokens[@]} - 1 ))]}"


Slicing Arrays
^^^^^^^^^^^^^^

https://stackoverflow.com/a/1336245/11003729

.. code-block:: bash

    A=( foo bar "a  b c" 42 )
    B=("${A[@]:1:2}")     # :1:2 takes a slice of length 2, starting at index 1.
    C=("${A[@]:1}")       # slice to the end of the array
    echo "${B[@]}"        # bar a  b c
    echo "${B[1]}"        # a  b c
    echo "${C[@]}"        # bar a  b c 42
    echo "${C[@]: -2:2}"  # a  b c 42 # The space before the - is necessary


associative arrays
^^^^^^^^^^^^^^^^^^

.. code-block:: bash

    declare -A fruits

    fruits["a"]="apples"
    fruits["b"]="berries"
    fruits["c"]="cherries"

    echo "${fruits['a']}" # apples

    # count of mappings
    echo "${#fruits[@]}" # 3

    # expands the values
    echo "${fruits[@]}" # apples berries cherries

    # expand the keys
    echo "${!fruits[@]}"