Re: [Help-bash] Wrong result for assign subarray to itself?

[Qu Wenruo]

-------- Original Message --------
Subject: Re: [Help-bash] Wrong result for assign subarray to itself?
From: Greg Wooledge <address@hidden>
To: Qu Wenruo <address@hidden>
Date: 2014年11月10日 21:36
> On Mon, Nov 10, 2014 at 05:31:44PM +0800, Qu Wenruo wrote:
> > $ words=('word1' 'word2' 'word3')
> > $ echo address@hidden
> > word1 word2 word3            # OK
> Your array assignment above is correct.  In general, you will want to use
> the form "address@hidden" with quotes when expanding the array.
Thanks for the tip.
> > $ address@hidden:1}
> This assignment probably doesn't do what you want.  You are not assigning
> to a new array here, but rather to a scalar/string variable.  So, bash
> expands the array to a list of words, then joins them together into a
> string.
>
> > $ echo address@hidden
> > word2 word3 word2 word3  # What happens here??!!
> > # Shouldn't the result be ('word2' 'word3') ??
> You get more information if you use declare -p instead of echo:
>
> imadev:~$ words=('word1' 'word2' 'word3')
> imadev:~$ address@hidden:1}
> imadev:~$ declare -p words
> declare -a words='([0]="word2 word3" [1]="word2" [2]="word3")'
>
> Your scalar assignment overwrote the contents of words[0] with the
> concatenated sub-list.  But words[1] and words[2] remained untouched.
Thanks for the explain, I'd better learn to use declare instead of echo 
for debugging.
> Now, if what you are *really* trying to do is to create a new array
> which is a sub-list of the prior array, then this is how you should
> have done it:
>
> words=("address@hidden:1}")
That's what I want, thanks a lot!

Thanks,
Qu
> Or, if what you are *really* trying to do is remove the 0th element
> from an existing array, do this:
>
> unset 'words[0]'
>
> The former creates a new array, with indices 0, 1, 2, etc.  The latter
> simply removes one element from the existing array, so the remaining
> indices will be 1, 2, 3, etc.  An array of this kind is called a "sparse
> array", and the indices may not be a contiguous sequence of integers.
>
> imadev:~$ words=(these are some "nice and neat" words)
> imadev:~$ unset 'words[1]'
> imadev:~$ declare -p words
> declare -a words='([0]="these" [2]="some" [3]="nice and neat" [4]="words")'