Redirect regex misbehaving when placeholder empty

Question

I have the following 2 redirects active:

/code-examples/(.*)
-> /tutorials/android/$1/

and

/code-examples/android/(.*)
-> /tutorials/android/$1/

The first one has a higher position, so the second will only be executed if the first one didn't apply. This works if there is something in the placeholders, i.e. /code-examples/page1 leads to /tutorials/android/page1.

The problems occur when the placeholders are empty. Just /code-examples or /code-examples/android WITHOUT the trailing slash leads to 404. With the trailing slash, I can see that it adds a second slash at the end, which results in /tutorials/android//.

How can I get the redirects to work properly with and without something in the placeholders?

Answer 1

• The problem with your RegEx patterns:

  /code-examples/(.*)
  /code-examples/android/(.*)
  

  is that they only match when the ending slash (/) is present in the URL; e.g.:

  # Example 1: $1 is 'page1'
  /code-examples/page1
  /code-examples/android/page1
  
  # Example 2: $1 is '' (empty)
  /code-examples/
  /code-examples/android/
  
  # Example 3
  # No matches because the ending / is not present.
  /code-examples
  /code-examples/android
  

  where the "placeholder" (i.e. (.*)) matches the page1 in the first example, and '' (i.e. empty string) in the second example.

• To make these work:

  /code-examples
  /code-examples/android
  

  you can use (?:/?(.*)|\b) instead of /(.*), like so:

  /code-examples(?:/?(.*)|\b)
  /code-examples/android(?:/?(.*)|\b)
  

• But since you redirect to the same URL (/tutorials/android/$1/), you can combine those RegEx patterns like so:

  /code-examples(?:/android|)(?:/?(.*)|\b)
  

  where /code-examples(?:/android|) matches either /code-examples or /code-examples/android.

I added the redirects with the Redirection plugin.

I suppose you have something like this on the Tools → Redirection → Redirects page (in wp-admin):

Now with the combined RegEx pattern, delete the second Redirect and edit the first one like so:

Note: For the Type and Group settings, just use your existing setup.

Resources:

• Redirect Regular Expressions: https://redirection.me/support/redirect-regular-expressions/

• https://regexr.com/41vch — for testing the combined RegEx pattern. But note that on RegExr, you need to use \/ and not just /. I.e. escape the / with a \.