Re: ZSH Local or Remote?

["Brian K. White" <brian@xxxxxxxxx>]

----- Original Message ----- 
From: "Steven Klass" <sklass@xxxxxxxxxxxxxxx>
To: "zsh-users" <zsh-users@xxxxxxxxxx>
Sent: Sunday, November 27, 2005 3:20 PM
Subject: ZSH Local or Remote?


> Hi all,
>
> Does anyone have a nice slick function to determine whether the  machine 
> you are logged on to is local or remote?  Basically you will  get the tty 
> of the current shell and grep for this in who or pinky.   If you get 
> :[0-9] you must be local.
>
> Clearly this isn't bullet proof but I was wondering if any of you  had a 
> really slick way of figuring this out..
>
> Why you ask?  If I am locally logged in I want to run keychain.  If a 
> person is remote AND the machine is a trusted_machine I want to run 
> keychain.  Otherwise don't...
>
> Keep in mind this needs to run multiplatform - so be carefull which 
> command you use..

I have something like that but it's not especially slick.
I have for example a case statement for what command line args and how to 
parse the output of the who command.
And it's in the form of 2 seperate scripts. tellip and amilocal

------------------
#!/bin/ksh
#
# tellip - "Tell IP"
# prints the IP or Hostname that the user is connecting from.
# mostly used in other scripts to determine non-static addresses.
#
# can be run on SCO, Linux, FreeBSD
#
# Brian K White - brian@xxxxxxxxx - Aljex Software

# facetwin screws up "who" so try to use facetwin variable instead.
[ -n "${FACETWINIPADDR}" ] && { echo "${FACETWINIPADDR}" ; exit ; }

# "who" tries to show hostname but chops long names, try to use ssh 
variable.
[ -n "${SSH_CLIENT}" ] && { echo "${SSH_CLIENT}" |awk '{print $1}' ; exit 
; }

case `uname -s` in
 Linux)  who -m |cut -d\( -f2 |cut -d\) -f1 ;;
 FreeBSD)  who |cut -d\( -f2 |cut -d\) -f1 ;;
 SCO_SV) who -umx | awk '{ print $6 }' ;;
esac
------------------

------------------
#!/bin/ksh
#
# amilocal - "Am I Local?"
# Detects if the user is connecting from inside or outside the local LAN.
#
# Requires "tellip"
#
# Brian K. White - brian@xxxxxxxxx - Aljex Software

TTY=`tty`
LOGFILE=/var/log/WAN-LOGINS
LOGGING=false
VERBOSE=false

for ARG in $@ ; do
   case ${ARG} in
       -l) LOGGING=true ;;
       -v) VERBOSE=true ;;
   esac
done

case ${TTY} in
   /dev/tty[1-9]|/dev/tty[012][0-9])
       ${VERBOSE} && echo "YES: TTY=`tty`"
       exit 0
       ;;
   *)
       IP=`tellip`
       ID=`id -un`
       grep -q ${IP} /etc/LAN && {
           ${VERBOSE} && echo "YES: IP=${IP}"
           exit 0
       } || {
           ${LOGGING} && echo "`date`\t${ID}\t${IP}" >>${LOGFILE}
           ${VERBOSE} && echo "NO: IP=${IP}"
           exit 1
       }
       ;;
esac
--------------


As you can see, /etc/LAN is a text file that lists ip addresses/hostnames on 
the lan with the server.
It starts as a copy of /etc/hosts (which lists all local subnet & vpn ip's 
that wouldn't be in dns)
It would be more automatic to parse ifconfig, but I want to deliberately 
leave out some ip's once in a while.
Still that could be done with a list of exclusions instead of a list of 
inclusions I guess, except I think a list of inclusions is safer.

At random times I find it handy to say "tellip" at the command line, or 
"amilocal -v"
or testing customers inbound nat/firewall from on-site, by connecting out to 
my bix and then "telnet `tellip` 25"  "ssh `tellip`" etc...
But it's main use is in /etc/profile where I set $AMILOCAL and $SRVIP and do 
some other lan vs wan changes like setting default print destination to 
passthru-print or not.
Then many many other places througout my software I just drop 
getenv("SRVIP") into urls and/or consult getenv("AMILOCAL") to decide which 
of 2 ways to do something or if something should be allowed or if something 
is even possible. $AMILOCAL gets used right of the bat in the users .profile 
in some cases to decide which starting point they get put into in the app.
$AMILOCAL && start_full_access || start_limited_access

I think it's just about impossible to make something like this that's really 
elegant and works everywhere.
The biggest problem is that you can not predict or know all the possible tty 
names and know whether they are local or not.
Multi-port serial cards and network serial server boxes have no end of types 
of names, various network servers produce different types of names.
Various session manager apps produce fake ttys of different types of names.
Equinox esp-16 for example, network serial box, lets you invent a tty name 
prefix of anything you like during driver install. It just checks to make 
sure it won't collide with something already existing.
Granted the serial terminal case is getting pretty rare and you could just 
do like I did and simply ignore it. Naughty. :)
I just check for the known console tty names. Another stanza would have to 
be added to the tty case statement for each make & model of serial card or 
serial server, and even if I wanted to look up every one currently existing, 
new ones get created and things like that equinox that let the user invent 
anything, makes it impractical. leave it for per-site customization and 
probably never need to do it anyways.

The facetwin note above is a lesson in assumptions.
In that case, the server daemon for a network telnet-ssh-alike actually puts 
the computers windows computer name, the netbios name, into the spot where 
utmp/wtmp readers (like who) look for the users ip/hostname. So it 
effectively makes who useless for that. But, at the same time it provides an 
env variable that does have the users ip, as seen from the servers point of 
view (it also has what the client thinks it's own ip is in another var so 
the distinction is not meaningless) so it's possible to have the script test 
for that and transparently provide the right answer.

Brian K. White  --  brian@xxxxxxxxx  --  http://www.aljex.com/bkw/
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