Nginx – How to use a variable in a regular expression in nginx

configurationnginxregex

I've spent some time trying to find the answer before writing this question:

I have several location blocks in my nginx config file that look like this:

location ~ ^/(doc|img|bla|foo)/metadata/$ { ... }

location ~ ^/(doc|img|bla|foo)/deleted/$ { ... }

location ~ ^/(doc|img|bla|foo)/something/$ { ... }

So I thought it would be a good idea to refactor the repeated regular expression into a variable that I set in the server section (also because I know I'll have to add to it in the future), like so:

server {
     set $my_regex doc|img|blah|foo;

     # I also tried this one:
     set $my_regex "doc|img|blah|foo";
     ....
}

Which I would then reuse inside the location blocks:

# this doesn't have any effect
location ~ ^/($my_regex)/metadata/$ { ... }

# this one neither
location ~ ^/(\$my_regex)/deleted/$ { ... }

# and this one neither
location ~ ^/(${my_regex})/something/$ { ... }

Any idea? Thanks!

Best Answer

There is no way to use variables in location matching.

If you want it, you probably doing something wrong. In this case you could try nesting locations.

Correct way in new versions of nginx

Turn out my first answer to this question was correct at certain time, but it turned into another pitfall - to stay up to date please check Taxing rewrite pitfalls

I have been corrected by many SE users, so the credit goes to them, but more importantly, here is the correct code:

server {
       listen         80;
       server_name    my.domain.com;
       return         301 https://$server_name$request_uri;
}

server {
       listen         443 ssl;
       server_name    my.domain.com;
       # add Strict-Transport-Security to prevent man in the middle attacks
       add_header Strict-Transport-Security "max-age=31536000" always; 

       [....]
}

Nginx – How to Output Variable in Log for Debugging

You can send nginx variable values via headers. Handy for development.

add_header X-uri "$uri";

and you'll see in your browser's response headers:

X-uri:/index.php

I sometimes do this during local development.

It's also handy for telling you if a subsection is getting executed or not. Just sprinkle it inside your clauses to see if they're getting used.

location ~* ^.+.(jpg|jpeg|gif|css|png|js|ico|html|xml|txt)$ {
    add_header X-debug-message "A static file was served" always;
    ...
}

location ~ \.php$ {
    add_header X-debug-message "A php file was used" always;
    ...
}

So visiting a url like http://www.example.com/index.php will trigger the latter header while visiting http://www.example.com/img/my-ducky.png will trigger the former header.

Best Answer

Related Solutions

NGINX Redirect – How to Rewrite All HTTP Requests to HTTPS While Maintaining Sub-Domain

Correct way in new versions of nginx

Nginx – How to Output Variable in Log for Debugging

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