How to reverse array in bash onliner FOR loop?

Question

How can I reverse the order in which I perform a for loop for a defined array

To iterate through the array I am doing this:

$ export MYARRAY=("one" "two" "three" "four") $ for i in ${MYARRAY[@]}; do echo $i;done one two three four 

Is there a function where I can reverse the order of the array?

One thought I had is to generate a sequence of inverted indexes and call the elements by using this reversed index but maybe there is a quicker alternative, or at least easier to read.

Answer 1

You can use the C-style for loop:

for (( idx=${#MYARRAY[@]}-1 ; idx>=0 ; idx-- )) ; do     echo "${MYARRAY[idx]}" done 

For an array with "holes", the number of elements ${#arr[@]} doesn't correspond to the index of the last element. You can create another array of indices and walk it backwards in the same way:

#! /bin/bash arr[2]=a arr[7]=b  echo ${#arr[@]}  # only 2!!  indices=( ${!arr[@]} ) for ((i=${#indices[@]} - 1; i >= 0; i--)) ; do     echo "${arr[indices[i]]}" done 

Answer 2

You can use tac, which is an opposite of cat in sense that it reverses the lines.

MYARRAY=("one" "two" "three" "four") for item in "$MYARRAY"; do    echo "$item";  done | tac  # four # three # two # one