Topic: Using IF-ELSE with ENV variables

[csdude55]

Hi all! Long time coder, first time poster to this board.

I'm not sure how Apache handles the order, but when I set an ENV prior to the IF-ELSE it doesn't appear to be read. Or maybe I'm reading it wrong. More below.

Also, when I run a regex in the IF, the %1 isn't being carried into the results.

Example:

[James Blond]

There is a good example answer here: https://stackoverflow.com/questions/42137409/apache-2-4-nested-if-directives

if you still have a question please ask again.

[csdude55]

Thanks, James. I'm afraid it doesn't help, though; it just confirms that nested IF-ELSE is OK, but doesn't say anything about using ENV variables or backreferences.

I should have stated before that I'm using 2.4.55

The saga has gotten even more confusing, though. It looks like the IF will actually delete previously assigned ENV? I discovered that if I remove the IF statement then I'll get a value for $_SERVER['linker'], but when I have the IF statement then $_SERVER['linker'] is gone; not empty, but appears to have never been set.

[tangent]

Re your attempt to use regex backreferences to help set environment variables:

The Apache documentation for expr https://httpd.apache.org/docs/current/expr.html says:

The strings $0 ... $9 allow to reference the capture groups from a previously executed, successfully matching regular expressions. They can normally only be used in the same expression as the matching regex, but some modules allow special uses.

So your "RewriteRule ^ - [E=tester:%1] " won't find %1 (nor $1) from expr.

What you can do though, is use SetEnvIfExpr, e.g.

[csdude55]

I see. So it'd have to duplicate the regex.

[tangent]

Reading established ENV variables within subsequent IF statements should be fine.

I sort of agree with your concern, but think the issue here is you can't reasonably expect regex back references from expr logic in an IF match statement, to be available to (or be honoured by) other module code enclosed within said logical blocks.

If you look at all the expr builtin functions, you'll see they're all read or lookup related, and don't write anything outside the expr scope.

Maybe that's why the developers came up with SetEnvIfExpr.

[tangent]

I've just read your last post more carefully, and wondered, why you've duplicated the regex?

You don't need the initial IF condition, since that's covered by the SetEnvIfExpr statement, or am I missing something?

[csdude55]

[csdude55]

Somewhat of an update...

I found that this will kinda work:

[James Blond]

it might be easier to set the env inside the vhost config

[tangent]

@csdude55 - further to your latest post (and James reply), which I've only just been able to respond to.

Through testing, I agree there are some inconsistencies with IF statements seeing Apache defined environment variables, depending on whether they are at a global level, or within a virtual host. Indeed, an IF env test within a vhost seems to circumvent an IF env test that otherwise works at the global level.

The expr documentation does have a section on "Environment variable ordering" which along with your findings suggests this approach is somewhat of a minefield.

Historically, I've stuck to mod_rewrite logic for environment variable manipulation, using rewrite conditions with appropriate flags, accepting you can't create configuration logic that reads as elegantly as IF-ELSE blocks, but at least it works as expected.

[James Blond]

I haven't tested it with the IF statements, but with all other things in apache: .htaccess overrides vhost that overrides global.

.htaccess
vhost
global