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--- htaccess_recipes [2022/02/14 03:16] – [Save the current directory as an environment variable] jquah
+++ htaccess_recipes [2022/02/23 21:41] – Added not about not applicable to nginx-served peteyboy
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 ====== .htaccess recipes ======
+:!: Note: .htaccess only works at SDF on pages served by Apache, which at the time of this writing (2022/02/23) is only on the cluster. Meaning that .htaccess will not do anything if placed in folders served by [[metaarray|The MetaArray]] or VHOST
 === Introduction ===
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 ===== Save the current directory as an environment variable =====
-If you made your website accessible via tilde-style URLs (running ''mkhomepg -d'' at the shell), then requests to anything under http://sdf.org/~YOURUSERNAME will have a different setting for DOCUMENT_ROOT than requests to the same content at http://YOURUSERNAME.sdf.org (assuming that ~/html and ~/public_html are symlinks to the same folder). A single htaccess serving both types of URLs cannot blindly make relative path substitutions in a RewriteRule directive (or even well-intentioned absolute path substitutions based on your knowledge of the SDF filesystem). Instead, you can first pass the requested URL through a do-nothing RewriteRule (the //pattern// ''^.*$'' matches everything, and the //substitution// ''-'' leaves it unchanged), extracting the current directory into the environment variable ''CWD''. Then you might use the value of ''CWD'' in a subsequent RewriteRule that performs an actual substitution. Here is an example:
+You might already be aware that the options in an htaccess file will affect all the files in subdirectories of the htaccess file location, unless overridden by htaccess files deeper into the path. But did you ever wish you could dynamically infer the location of your base htaccess file, for substitution into later directives? It turns out that Perl regexes (used in Apache's mod_rewrite) are flexible enough to do the trick.
+If you made your website accessible via tilde-style URLs (running ''mkhomepg -d'' at the shell), then requests to anything under http://sdf.org/~YOURUSERNAME will have a different setting for DOCUMENT_ROOT than requests to the same content at http://YOURUSERNAME.sdf.org (assuming that ~/html and ~/public_html are symlinks to the same folder). A single htaccess serving both types of URLs cannot blindly make relative path substitutions in a RewriteRule directive (or even well-intentioned absolute path substitutions based on your knowledge of the SDF filesystem). Instead, you can first pass the requested URL through a do-nothing RewriteRule (the //pattern// ''^.*$'' matches everything, and the //substitution// ''-'' leaves it unchanged), extracting the current directory into the environment variable ''CWD''. Then you can use the value of ''CWD'' in a subsequent RewriteRule that performs an actual substitution. Here is an example:
 <code>
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 This example can be extended to perform different redirections depending on which virtual host handled the transaction (just create a new stanza with a different condition on %{HTTP_HOST}). In this way you can give your visitors the same experience whether they've bookmarked your site as http://YOURUSERNAME.sdf.org or http://sdf.org/~YOURUSERNAME, without having to duplicate your content in multiple folders.
+Because these RewriteRules impose additional processing demands on the server for each request, hacks like these should be a last resort. If the other workarounds mentioned in [[custom_error_pages_for_your_site|custom error pages for your site]] address your use case, they should be implemented instead.
 ===== Add (or force) MIME-type =====