How to use a variable in a regular expression in nginx?

Question

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!

Solution

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.

Comments

[Admin]

Greetings! Just interesting: did You try to combine two expressions in one? location ~ ^/(doc|img|bla|foo)/(metadata|deleted|something)/$ { ... }

[Admin]

@SergeySerov No, I'm not going that far. I'm just trying to refactor the regular expression that has been used three times by assigning it to a variable that I then would like to use in the location directive.

[Admin]

@SergeySerov Actually I now have combined them into one, and use a rewrite. But that doesn't solve the initial problem. :-)

[jfix]

I don't think I'm looking for named captures. From what I understand, named captures allow to reference a matched part of a regex by name rather than by a numeric index in later processing. Here however I'm looking for the possibility to reuse an existing variable inside a regex. Maybe that's just not possible?

[jfix]

@AlexeyTan I've reduced the use of the regex to only two occurrences which will make the pain of maintaining somewhat more bearable. But I guess I have to find another solution, maybe scripting?