Re: a 'who called me?' variable?

[Craig Dickson <crdic@yahoo.com>]

Dan Berdine wrote:

> Is there an environment variable in bash that can be used to tell where 
> bash is running from?  For example, is there a variable I can test in 
> my .bashrc to tell whether I am running remotly, from a tty, from 
> konsole, an xterm, etc.?  I'v looked at the Advanced Scripting HOWTO, 
> but the only thing that looked promising was "$BASH_ENV" which seems to 
> be empty.

I use the following script, which determines the appropriate value for
the DISPLAY variable (for the benefit of X apps) appropriately according
to how I'm accessing the system. It probably isn't perfect (I'm sure if
you have two monitors, it may screw up, or if you're on a graphics
terminal connected by a serial line, or some other unusual connection),
but it works for me.

--- cut here ---
#!/bin/sh
#
# getdisp
#
# by Craig Dickson
# crdic@yahoo.com
# 2001.07.13
#
# This script determines a good value for the DISPLAY variable, and echos
# it to stdout.
#
# Note that the SSH_CLIENT shell variable is not normally exported, and
# therefore will not be available in a subshell. Also, the PPID variable
# will be different in a subshell. Because of these facts, it is best to
# source this script, as in "export DISPLAY=$(source getdisp)".

unset disp

# If you are logged in via ssh, then the SSH_CLIENT variable will contain,
# among other things, your remote IP.

if [ -n "$SSH_CLIENT" ]; then
    echo "getdisp: display determined by SSH_CLIENT." >&2
    disp=$(echo $SSH_CLIENT | cut -d " " -f 1):0.0

# Otherwise, if you are in some sort of xterm session (including rxvt or
# gnome-terminal), then the COLORTERM variable will be set, or TERM=xterm,
# and netstat can be used together with the PPID variable to find your
# remote IP. Interestingly, this also works if your xterm session is at
# the console, because there will be no network connection associated with
# your PPID, so your display will be correctly identified as :0.0 (as long
# as you have only one display...).

elif [ -n "$COLORTERM" -o "$TERM" = "xterm" ]; then
    echo "getdisp: display determined by X terminal PPID." >&2
    disp=$(netstat -np --tcp 2>/dev/null | grep " $PPID/")
    disp=$(echo $disp | cut -d " " -f 5 | cut -d ":" -f 1):0.0

# Otherwise, we try to use 'last' to figure out where you're connecting from.
# This has to be done in one of two forms. Neither is guaranteed to work.
# If both fail, nothing will be echoed.

else
    disp=$(last -20ai | grep $USER | head -1 | cut -c 61-):0.0

    if [ "$disp" = "0.0.0.0:0.0" ]; then
        echo "getdisp: display determined by last -a." >&2
        disp=$(last -20a | grep $USER | head -1 | cut -c 61-)
    else
        echo "getdisp: display determined by last -ai." >&2
    fi
fi

if [ -n "$disp" ]; then
    echo $disp
fi

unset disp
--- cut here ---