Description of problem:
I use zsh and for quite some time, I have been having issues with an internal zsh facility that lets you print the hostname (namely print -P "%M).
On some of my F9 hosts it would work and on some others it wouldn't.

After investigating, it appears keychain in /etc/profile.d/keychain.sh not only overwrites HOST but it also unset it before it exits.

Issue is HOST is defined by the shell (document under "PARAMETERS SET BY THE SHELL" section in the manpage) so it expects it to be present.

If HOST isn't defined, print -P "%M" doesn't work:
%echo $HOST

%print -P "%m %M"

%HOST=foobar
%print -P "%m %M"
foobar foobar


Version-Release number of selected component (if applicable):
keychain-2.6.8-3.fc9.noarch

How reproducible:
Always if you have keychain enable (aka ~/.keychainrc).

Steps to Reproduce:
1. use zsh as your shell
2. have ~/.keychainrc
3. open a new session, HOST is undefined
  
Actual results:
keychain.sh overwrites HOST even though it's already set, then it unset it.

Expected results:
I guess it shouldn't replace the value of HOST if it's already there and above all it shouldn't delete it.

This is what I propose:

--- /etc/profile.d/keychain.sh.orig     2008-04-06 18:09:07.000000000 +0200
+++ /etc/profile.d/keychain.sh  2008-09-25 13:13:12.000000000 +0200
@@ -24,13 +24,13 @@
        keychain $KCHOPTS $SSHKEYS $GPGKEYS
     fi
 
-    HOST=`uname -n`
+    [ -n "$HOST" ] || HOST=`uname -n`
     [ -f $HOME/.keychain/$HOST-sh ] && \
        . $HOME/.keychain/$HOST-sh
     [ -f $HOME/.keychain/$HOST-sh-gpg ] && \
        . $HOME/.keychain/$HOST-sh-gpg
 
-    unset KCHOPTS SSHKEYS GPGKEYS HOST
+    unset KCHOPTS SSHKEYS GPGKEYS
 
     KEYCHAIN_DONE=1
 fi