Re: currently doable? Indirect notation used w/a hash

[Pierre Gaston]

On Mon, Jun 10, 2013 at 1:37 PM, Pierre Gaston <pierre.gaston@gmail.com> wrote:
> On Mon, Jun 10, 2013 at 12:43 PM, Linda Walsh <bash@tlinx.org> wrote:
>>
>>
>> Pierre Gaston wrote:
>>
>>> bash4 has associative arrays:
>>>
>>> declare -A array
>>> array[foobar]=baz
>>> echo "${array[foobar]}"
>>
>> ---
>>
>> Right, and bash's namespace is also an associative array -- names & values.
>>
>> In the main namespace you can use '!' to introduce indirection,
>> but not in a generalized way.
>>
>> i.e. a=foo ${!a}=1; echo $foo => '1'
>>
>> What I found myself wanting was having several 'sets' of
>> the same parameters of info.  so I could have
>> multiple hashes or associative arrays,
>>
>> eth0=([ip]=1.2.3.4/24  [mtu]=1500  [startmode]=auto)
>> eth1=([ip]=192.168.0.1/24  [mtu]=9000 [startmode]=onboot)
>>
>> Then wanted to be able to pass which interface to work on, into
>> a function i.e. pass in 'eth0' or 'eth1'... etc.
>>
>> In the function, the parameter would be in a var maybe "IF".
>>
>> Now I want to access the value for IP for the current "IF" (IF holding
>> eth0 or eth1 or some other InterFace name).
>>
>> i.e.
>> IF=eth0;  echo "${!IF[IP]}"
>>
>> but that doesn't work.  You need secondary dereferencing, like:
>>
>> eval echo \${$IF[IP]}
>>
>> I ended up using a sub, since after reading in some config files
>> 99% of my usage is reading, so like:
>>
>> sub read_n_apply_cfg () {
>>         my file="${1:?}"
>>         my this="cfg_$file"
>>         eval "hash -g $this"  <- creates per item hash/assoc. array
>> (assigned somewhere later)
>>
>>         #accessor
>>         sub this () { eval echo "\${$this[$1]:-""}" ;} <- hide indirecton in
>> sub
>>
>> usage:
>>         local ip=$(this ip)  #(with '$this' set at top of routine)
>>
>> ------
>> A bit contorted, but anyone doing shell programming has to be
>> used to that.  ;-)
>>
>
> Well, it's easier to ask for what you really want first.

my apologies, I misread "name of a hash" and read pass a hash and
thought you were just after an associative array