Reason why the first element of a Zsh array is indexed by 1 instead of 0

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From my experience with modern programming and scripting languages, I believe most programmers are generally accustomed to referring to the first element of an array by 0 as index.
Are there any substantial advantages in using 1?

I'm sure I've heard of more languages other than Zsh behaving similarly with arrays; it's fine by me, as it is equally convenient.
However, as previously released and widely used shell scripting languages such as ksh and bash all use 0, why would someone choose to alter this common "standard"?

My immediate answer to my question would be "of course not";
then, the only explanation I can think of regarding this somewhat "exclusive feature" to shells would be "they just did this to show off a bit more their cool shell".

I don't know much of either Zsh or its history though, and there is a high chance my trivial theory about this does not make any sense.

Is there an explanation for this? Or is it just out of personal taste?

Best Answer

Virtually all shell arrays (Bourne, csh, tcsh, fish, rc, es, yash) start at 1. ksh is the only exception that I know (bash just copied ksh).
Most interpreted languages at the time (early 90s): awk, tcl at least, and tools typically used from the shell (cut -f1-3, head -n 3, sort -k1,3, cal 1 2015, comm -1) start at 1. sed, ed, vi number their lines from 1...
zsh takes the best of the Bourne shell and csh. The Bourne shell array $@ start at 1. zsh is consistent with its handling of $@ (like in Bourne) or $argv (like in csh). See how confusing it is in ksh where ${@:0:1} does not give you the first positional parameter for instance.
A shell is a user tool before being a programming language. It makes sense for most users to have the first element in $a[1]. It also means that the number of elements is the same as the last indice (in zsh like in most other shells except ksh, arrays are not sparse).
a[1] for the first element is consistent with a[-1] for the last.

So IMO the question should rather be: what got into David Korn's head to make its arrays start at 0?

Related Solutions

Bash – way of reading the last element of an array with bash

As of bash 4.2, you can just use a negative index ${myarray[-1]} to get the last element. You can do the same thing for the second-last, and so on; in Bash:

If the subscript used to reference an element of an indexed array evaluates to a number less than zero, it is interpreted as relative to one greater than the maximum index of the array, so negative indices count back from the end of the array, and an index of -1 refers to the last element.

The same also works for assignment. When it says "expression" it really means an expression; you can write in any arithmetic expression there to compute the index, including one that computes using the length of the array ${#myarray[@]} explicitly like ${myarray[${#myarray[@]} - 1]} for earlier versions.

Shell – Accessing random array element in ZSH

feh is an image viewer, just ignore that part... you want just the second part.

Basically, to access a random array element you want something like ${arr[${ri}]} where ri is $(( $RANDOM % ${#arr[@]} + 1)) that is, ri is a random index of the array arr

Now, $RANDOM % N resolves to a random number from 0 to N-1. In this case N is the array length ${#arr[@]} (number of elements) but since array indexing starts from 1 in zsh you have to add one ( + 1) so that $(( $RANDOM % ${#arr[@]} + 1 )) returns a value from 1 to N.

So e.g. to print a random element of the array:

print -r -- ${arr[$(( $RANDOM % ${#arr[@]} + 1 ))]}

Or simply, as array indices are parsed as arithmetic expressions:

print -r -- "$arr[RANDOM % $#arr + 1]"

When using that csh-style syntax (when the expansion is not in braces), the quotes are necessary in order for zsh to parse the subscript; alternatively, this could be written $arr[RANDOM%$#arr+1] or ${arr[RANDOM % $#arr + 1]} (ksh-style).

Best Answer

Related Solutions

Bash – way of reading the last element of an array with bash

Shell – Accessing random array element in ZSH

Related Question