Re: Compare 2 arrays.

[Greg Wooledge]

On Tue, May 29, 2012 at 09:25:02PM -0600, Bill Gradwohl wrote:
> I have no idea what the wget's are supposed to be doing, but here's a
> function that will compare 2 foreign arrays and return true 0 or false 1.
> 
> compareForeignArrays(){
>    ## $1 and $2 are the names of the arrays to compare.
>    ## These are characters strings.
> 
>    local intermediary
>    local sub
> 
>    intermediary="${1}[@]"
>    local -a leftValue=("${!intermediary}")

Hacks like this are precisely why I stress that such functions *should
not* be written in bash.  If you want to compare two arrays, use a loop,
without wrapping a function around it.  That way you have access to the
arrays directly, by their actual names, in the actual context where they
are defined.

The only Bourne-family shell that can manipulate arrays whose names are
passed to a function is ksh93, with its "nameref" command.  Bash has
nothing analogous to that yet.

I don't know whether the tmp="$1[@]"; x=("${!tmp}") trick is a bug or
a feature.  It's certainly undocumented.  I don't know whether it will
go away in some future version of bash, with or without a notification in
the changelog, since it looks like a bug that people are exploiting.