Bash - Get last index of array

Question

In Bash how can one get the last index of an array?

This works: $((${#array[@]} - 1)) but is not very pretty.
To get the last element of an array one can do ${myarray[-1]} is there a similar option for index?

take a look at this Q&A re: is array sparse/dense; part of the req is to find the last index; Socowi's answer refers to a custom builtin that could be modified to return the last index; my answer, along with a slew of comments, looks at a few ideas for finding the last index (ie, basically parsing the output from typeset -p); keep in mind we were looking at performance related issues for large arrays; for (relatively) small arrays any of the ideas presented at that link would likely be sufficient for this OP's req — markp-fuso
– markp-fuso, Commented Aug 22, 2021 at 14:18
should probably update the question to verify if this is (not) an associative array; assuming a (relatively) small (associative) array, one brute force idea: printf "%s\n" "${!array[@]}" | sort -n | tail -1 — markp-fuso
– markp-fuso, Commented Aug 22, 2021 at 14:27
Is there a way of reading the last element of an array with bash? explains negative indices. — joharr
– joharr, Commented May 9, 2024 at 12:35

Shawn · Accepted Answer · 2021-08-22 17:38:40Z

8

If you're working with sparse arrays that have had elements unset:

indexes=( "${!array[@]}" )
lastindex=${indexes[-1]}

otherwise your $((${#array[@]} - 1)) is the way. Shell isn't pretty.

answered Aug 22, 2021 at 17:38

Shawn

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Shawn Over a year ago

If using zsh instead of bash, it's lastindex=${(k)array[-1]}

Léa Gris · Accepted Answer · 2021-08-22 17:41:25Z

1

Get the last index of an array, regardless if it is sparse or not:

#!/usr/bin/env bash

array=([4]=foo [1]=bar [5]=cux [0]=baz)

# Capture all the indexes of the array
arrindexes=("${!array[@]}")

# Print the last index and element
last_index=${arrindexes[-1]}
printf 'Last index is: %d\n' "$last_index"
printf 'Last element at index %d is: %s\n' "$last_index" "${array[last_index]}"

answered Aug 22, 2021 at 17:41

Léa Gris

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