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From: tsilva%aaec1.UUCP@DSPVAX.MIT.EDU (Tony Silva)
Newsgroups: gnu.emacs.help,comp.emacs
Subject: Re: accessing environment variables in Lisp expressions (SUMMARY)
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Date: 7 May 91 15:15:59 GMT
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I received several excellent suggestions for avoiding hardwiring home
directory names, etc., in my ~/.emacs file, as in:

    (setq mail-archive-file-name "/u/tsilva/SMAIL")

The key Lisp functions are "substitute-in-file-name",
"expand-file-name", and (I'm embarrassed to say I never thought of
this one) "getenv". (I had tried using "command-apropos" and searching
through the Emacs topics using Info Reader, but apparently didn't try
hard enough.). Any of the following can be used in place of the
expression above:

    (setq mail-archive-file-name (substitute-in-file-name "$HOME/SMAIL"))
    (setq mail-archive-file-name (expand-file-name "~/SMAIL"))
    (setq mail-archive-file-name (concat (getenv "HOME") "/SMAIL"))

I'm particularly fond of "expand-file-name" since the csh-like tilde
expansion permits easy reference of other users' home directories, as
well.

Another useful tidbit that was mentioned was:

(setq host-name (substring (system-name) 0 (string-match "\\." (system-name))))

to yield the base portion of the current system name, ultimately for
invoking host-specific code.

Many thanks to all those who took the time to respond:
haydens%bullwinkle@xn.ll.mit.edu (Hayden Schultz)
rms@gnu.ai.mit.edu (Richard Stallman)
raymond@math.berkeley.edu (Raymond Chen)
Paul Palmer <palmerp@MATH.ORST.EDU>
rsw@cs.brown.edu (Bob Weiner)
eirik@theory.TN.CORNELL.EDU (Eirik Fuller)
mittal@ISI.EDU
Hamish Macdonald <himacdon@maytag.waterloo.edu>
Jim Hudgens <hudgens@sun13.scri.fsu.edu>
brookler@lentil.Berkeley.EDU (David Brookler)
Scott Brim <swb@nr-tech.cit.cornell.edu>
jimb@gnu.ai.mit.edu (Jim Blandy)
Olaf Bigalk <bigalk@opal.cs.tu-berlin.de>
Tim Bradshaw <tim@cstr.edinburgh.ac.uk>
spencer@spline.eecs.umich.edu
Scott Blachowicz <hp.com!hpubvwa.nsr.hp.com!grlab!scott@relay.MIT.EDU>
mark3@mtfme.att.com (Mark Hord)
mike-w@cs.aukuni.ac.nz