[Wylug-help] Conditional forward suggestions

[Gary Stainburn]

Hi folks.

I currently have a .forward file that always delivers emails to my main 
mailbox for use when at my PC using kmail.

It then filers out as much rubbish as it can before forwarding to my gmail 
account so I can access it from my phone.

What I'm looking for is some way of disabling the forward to gmail if I'm 
currently at my PC.

This gives me two problems, 

1) how do I detect when I'm at my PC? 

2) how do I disable / enable the forwarding?

For this I was thinking of using a trigger file created / deleted by whatever 
method I get for (1) above. Then within my .forward check to see if this file 
exists.

Can anyone say how I could do something like the following in a .forward file

if <trigger file exists>
  seen
  finish
endif

Googling has only shown me exim.conf code but nothing to go in a .forward

Gary