Defining certain constants to be domain-agnostic is a sufficiently common practice to warrant consideration.

For example, the config file in markjaquith/WordPress-Skeleton has the following line:

define( 'WP_CONTENT_URL', 'https://' . $_SERVER['HTTP_HOST'] . '/content' );

If you run wp without passing a --url parameter, you will get a warning:

Notice: Undefined index: HTTP_HOST in /Users/User/.composer/vendor/wp-cli/wp-cli/php/wp-cli.php(20) : eval()'d code on line 19

Several workarounds were discussed in #676 (comment).

We already try to guess the URL by doing some ugly wp-config.php parsing via regular expressions.

A more reliable way would be to do a database query:

• need to account for the case where WP isn't installed yet; see Bug: wp core install allows --url to be empty #663
• need to account for multisite