Mountain Lion: how set environment variables

Question

Am I correct that for Mountain Lion, if not earlier, the only way to set environment variables at the system level is to use (or create) a file /etc/launchd.conf that contains commands such as:
setenv CATALINA_BASE /opt/local/share/java/tomcat6
(That does seem to work as expected.)
If so, how does one do this by referencing the value of something else, e.g., to set JAVA_HOME? I tried
setenv JAVA_HOME $(/usr/libexec/java_home)
but then in Terminal if I run
echo $JAVA_HOME
I just get back $(/usr/libexec/java_home).
By contrast, if I put that same setenv JAVA_HOME $(/usr/libexec/java_home) command into my ~/.profile, then the result of echo $JAVA_HOME is the actual value referenced, namely, /Library/Java/JavaVirtualMachines/jdk1.7.0_15.jdk/Contents/Home.

Answer 1

Linc Davis wrote:
launchd is not a shell and does not peform expansion. You have to use literal expressions. But you can also modify the bash environment system-wide by editing the file /etc/profile.
But sudo emacs /etc/profile won't let me edit this file: it's read-protected, emacs says.
What permissions should I give it? Right now it's in group wheel, owned by root but with Read permission only.
P.S. And is it really a good idea to edit /etc/profile -- assuming I can suitably set the permissions to do so? Apple goes out of its way to try to hide this file: /etc is a link to /private/etc, e.g.