Re: tail and grep

[Craig Sanders <cas@taz.net.au>]

On Tue, 7 Jul 1998, Patrick Olson wrote:

> when I try tail -f /var/log/messages | grep "local  IP"
> 
> it prints (with a real IP address instead of 123.123.123.123)
> 
> Jul  7 20:06:00 server2 pppd[587]: local  IP address 123.123.123.123
> 
> on my console.  That's exactly what it should do.  But if I try to
> redirect it to a user's file (so he can see what his dynamic IP is) using
> 
> tail -f /var/log/messages | grep "local  IP" > /home/pppusers/dynamic.IP
> 
> it does nothing but create a 0 byte file.
> 
> Questions:
> 
> 1. What am I doing wrong?
> 
> 2. Is there a way I can put this in the background so I don't have to
> remain logged in as root?

i think you've got the wrong "solution" to the problem....in other words,
there are better ways of doing what you want.

why not do this in /etc/ppp/ip-up (or /etc/ppp/ip-up.d if you are
running hamm)?

add lines like these to /etc/ppp/ip-up:

	DYNFILE=/tmp/dynamic.IP

	# first, delete the file just in case some evil user has it symlinked to 
	# a system file (like /etc/passwd or /bin/bash):
	
	rm -f $DYNFILE

	echo "$4" >$DYNFILE
	chmod a+r $DYNFILE

if this is for a dialin user (and not for a local console user who
you've given ppp dialout access to) then you probably need to find out
what their home directory is and put the dynamic.IP file in there.

try something like this instead:

	USER=`w | grep "$1" | awk '{print $1}'
	DYNFILE=/home/$USER/dynamic.IP

	rm -f $DYNFILE

	echo "$4" >$DYNFILE
	chown $USER $DYNFILE
	chmod a+r $DYNFILE

(note: these sh script fragments are untested.  use as a guideline only.
don't expect them to work as is. RTFM and understand what it does before
you trust any random code posted by a complete stranger on a mailing list)


the /etc/ppp/ip-up script is passed the following parameters from pppd when
the connection is established.  that is where the "$1" and "$4" above come
from.

# This script is called with the following arguments:
#    Arg  Name               Example
#    $1   Interface name     ppp0
#    $2   The tty            ttyS1
#    $3   The link speed     38400
#    $4   Local IP number    12.34.56.78
#    $5   Peer  IP number    12.34.56.99

there's also a 6th argument for recent (hamm only, i believe) versions of
pppd.  i have no idea what it's for.


#    $6   Optional ``ipparam'' value    foo


craig

--
craig sanders


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