jigdo - avoid unneeded .iso rebuild

[Carl Karsten <carl@personnelware.com>]

I am trying to figure out how to poll a web server and only run the a process 
(see below) when the .jigdo file has been updated.

I can get the Last-Modified timestamp from the server, and I can parse the 
output from wget looking for "Server file no newer than local file" but I am 
hoping there is a more elegant way.


$ curl --head  http://cdimage.ubuntu.com/daily/current/edgy-alternate-i386.jigdo
HTTP/1.1 200 OK
Date: Mon, 11 Sep 2006 23:15:50 GMT
Server: Apache/2.1.3 (Ubuntu)
Last-Modified: Mon, 11 Sep 2006 06:34:10 GMT
ETag: "3c5c002-1ee7d-bede1c80"
Accept-Ranges: bytes
Content-Length: 126589
Content-Type: text/plain


$ wget -N  http://cdimage.ubuntu.com/daily/current/edgy-alternate-i386.jigdo
--18:19:49--  http://cdimage.ubuntu.com/daily/current/edgy-alternate-i386.jigdo
           => `edgy-alternate-i386.jigdo'
Resolving cdimage.ubuntu.com... 195.248.90.25, 195.248.90.24
Connecting to cdimage.ubuntu.com|195.248.90.25|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 126,589 (124K) [text/plain]
Server file no newer than local file `edgy-alternate-i386.jigdo' -- not retrieving.


Current script I would like run soon after a new .jigdo is posted.  do I really 
need to rm the previous files?

# update edgy-alternate-i386.iso
cd new
rm edgy-alternate-i386.jigdo edgy-alternate-i386.template jigdo-file-cache.db
jigdo-lite --scan ../alternate 
http://cdimage.ubuntu.com/daily/current/edgy-alternate-i386.jigdo

cd ..
umount alternate
mv -f new/edgy-alternate-i386.iso .
mount alternate


Carl K