Forum OpenACS Q&A: ad_host before page is loaded...

It's almost certainly cleaner & better to make it a proc instead.  Can you be more specific?

You'd have to do some timing to see if this is going to adversely effect your performance, but I'd guess that 10 or so regexp calls would be less expensive than a single db query.

My first step if it turned out to need optimization would be to have ad_host store its regexp results in a ns_set.  You'd want to time that as well.

If you really really want to have variables pre-declared for you the only way I know of is to have a registered proc that computes your variables and then sources the requested script.

like I said, "If you really really want to have variables pre-declared for you the only way I know of is to have a registered proc that computes your variables and then sources the requested script." look up the docs on ns_register_proc... you could probably register something like this:

proc serve_with_ad_host { url } {
    # url will have the form /foo/bar.tcl
    set file [string range $url 1 end] ;# trim the /
    set host [ad_host] ;# precompute this
    source [file join [ns_info pageroot] $file]
}

(when you source a script it's exactly like inserting the script's code at your current execution point.)

doing this you can either make host global or use upvar/uplevel. global is the cleanest, followed by upvar, but both require you to explicitly call them which you seem reluctant to do. You could make a proc such as

proc global_host {} {
    global host
    return $host
}

but that's starting to get silly to avoid the overhead of something as simple as regexp or ns_set lookup.