[Info-vax] DCL, was: Re: Microkernel

[Simon Clubley]

On 2012-08-11, ChrisQ <meru at devnull.com> wrote:
> On 08/10/12 12:18, Simon Clubley wrote:
>
>>
>> (Before anyone suggests it, you cannot just dump the whole recall buffer to
>> a file; think about the sequence of events when you have multiple DCL
>> sessions going at the same time (with their unique commands entered
>> during the course of that session), and what will happen when you exit
>> the sessions one by one.)
>>
>> Simon.
>
> I guess you could if you use the pid of the session as key. Multiple bash
> sessions seem to handle that quite well...
>

The problem is that the combined entire history (up to a limit) from all
previous sessions is loaded into any new session. In bash, when you exit
a session, bash knows which commands were entered during the new session
and only adds those new commands to the combined history file, even though
there can be several thousand commands in the bash recall buffer.

In VMS, when you write out the recall history to a file, there's no way to
isolate the commands entered at the DCL prompt during the current session
from those loaded into the recall buffer at the start of the session.

Therefore, you would have to write out the full recall buffer and each
DCL session would write out it's own version of the full recall buffer.

This would effectively clobber the history from any other DCL session
which had been running at the same time (even if you allowed the history
to be appended into what would quickly become a _massive_ history file)
as you can only reload a maximum of 254 commands back into the recall
buffer.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
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