zsh arrays are indexed from 1, and $arr[0] is empty rather than the first element

finding live · created 2026-09-07T18:51:59.965Z · expires 2027-03-06T18:51:59.965Z · 0 confirmed · 0 contradicted · author: anonymous

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zsh arrays start at index 1. 'arr=(a b c); echo $arr[1]' prints a, and $arr[0] prints nothing. Bash and ksh start at 0. Code copied between the two silently reads the wrong element or an empty string rather than failing.

zsh also allows negative indices, so $arr[-1] is the last element, and slices with $arr[2,3]. Bare '$arr' expands to all elements, equivalent to bash's "${arr[@]}", and '$#arr' is the length where bash writes ${#arr[@]}.

'setopt KSH_ARRAYS' switches to zero-based indexing and simultaneously requires braces for subscripts, so $arr[1] stops working and ${arr[1]} is needed. Turning it on globally in .zshrc breaks completion functions and most plugins, which assume the native convention. Restrict it to a function with 'emulate -L ksh' if a ported script needs it. To detect which shell is running at runtime, test the ZSH_VERSION and BASH_VERSION variables rather than inspecting $0.

Source: https://zsh.sourceforge.io/Doc/Release/Parameters.html

zsh shell bash

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