let unset array element remove compatible with bash

let unset array element remove compatible with bash

[Daniel Lin]

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As we know, bash is very common on Linux world.
So, even I've moved to zsh.
But, I wish my script could be compatible with bash.

Today, I found the array element remove is not compatible with bash.
Can any developer consider to enhance zsh's function like "unset var[2]"?

Here is the sample


  $var[1]="four" ; var[2]="seven" ; var[3]="Four and
Seven"
  $for v in "${var[@]}" ; do echo "$v" ;
done

four


seven

  Four and
Seven
  $for v in "${var[*]}" ; do echo "$v" ;
done
  four seven Four and
Seven
  $echo "${#var[@]} ${#var[1]} ${#var[2]} ${#var[3]}"  # get
lengh
  3 4 5
14
  $unset var[2] ###### BASH only delete one
element
  $var[2]=() ###### ZSH only delete one
element
  $echo "${#var[@]} ${#var[1]} ${#var[2]}
${#var[3]}"
  2 4 0 14

Another note, I wish the FAQ in zsh can explain this incompatible with bash.

$echo "${#var[@]} ${#var[1]} ${#var[2]} ${#var[3]}"  # get lengh  work both
bash/zsh
$echo "$#var $#var[1] $#var[2] $#var[3]"  # get lengh  work only zsh

Re: let unset array element remove compatible with bash

[Bart Schaefer]

On Feb 22,  3:28am, Daniel Lin wrote:
}
} Can any developer consider to enhance zsh's function like "unset var[2]"?
} 
}   $unset var[2] ###### BASH only delete one element
}   $var[2]=() ###### ZSH only delete one element

I've started a thread on zsh-workers about this, but:

var[3]=() does not mean the same thing that unset var[3] would imply.

In zsh, if you assign to a position that is "off the end" of the array,
zsh manufactures empty array elements to "fill in the gap".  Try this
in each of bash and zsh:

    unset gappy
    gappy[9]=nine
    for g in "${gappy[@]}"; do echo /$g/; done

Now in zsh:

    unset gappy
    gappy=(one)
    gappy[3]=()
    for g in "${gappy[@]}"; do echo /$g/; done

Note that assigning an empty array to the one-element slice gappy[3]
has caused gappy[2] to exist as an empty element.

Bash is using some kind of sparse structure to store its arrays.

Re: let unset array element remove compatible with bash

[Chet Ramey]

On 2/22/12 12:41 AM, Bart Schaefer wrote:

> Bash is using some kind of sparse structure to store its arrays.

FWIW, bash uses a doubly-linked list.


-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/