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Re: Detect whether attached or detached from screen session?

From: Mark Eichin
Subject: Re: Detect whether attached or detached from screen session?
Date: Tue, 14 Oct 2008 11:41:00 -0400
User-agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux)

Peder Stray <address@hidden> writes:

> On Tue, 14 Oct 2008, Trent W. Buck wrote:
>> "Sven Hazejager"
>> <address@hidden> writes:
>>> I'm using screen to keep some applications open over a remote SSH
>>> connection that sometimes is killed. What I would like to do, is to
>>> somehow find out whether I am logged in (attached) or disconnected
>>> from the screen session.
>>> Reason is that I want procmail to send incoming mail to my BlackBerry
>>> if I'm disconnected, but NOT do that when I'm SSH-ing into my Pine
>>> session.
>> I don't know how to achieve that, but perhaps there's a different
>> approach to the problem -- such as always forwarding all mail to an
>> IMAP server that you can access from both the blackberry and from
>> pine.
> The screen-socket has execute permissions when attached, and none when
> detached, like this:
> attached:
> ls -l /tmp/uscreens/S-peder/4598.irc
> prwx------ 1 peder peder 0 Oct 14 00:00 /tmp/uscreens/S-peder/4598.irc
> detached:
> ls -l /tmp/uscreens/S-peder/4598.irc
> prw------- 1 peder peder 0 Oct 14 07:06 /tmp/uscreens/S-peder/4598.irc
> Guess you can test for that i procmail by something like:
> :0c
> *? perl -e 'exit ! grep { (stat $_)[2] & 0100 } </tmp/uscreens/S-peder/*>'
> address@hidden

Parsing "screen -ls" output (for "Attached" or not) might be less
sensitive to implementation details, but that's a pretty clever test...

I'm not familiar with procmail, but it might be cleaner to use

  ! test -x /tmp/uscreens/S-peder/*

(to avoid starting perl on every message - I think both of these
assume there's only one socket that matches the rule, though it's
pretty easy to change if not...)

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