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+---
+title: Asset Pipeline
+---
+
+PieCrust comes with a simple, yet efficient, asset pipeline. If you have
+advanced requirements, or want to use something familiar, you can of course use
+well known systems like [Grunt][] or [Gulp][], but you should definitely give
+the PieCrust asset pipeline a try.
+
+The PieCrust asset pipeline doesn't require a build file: asset processors are
+enabled more or less globally, and will affect all assets the same way inside a
+given asset directory.
+
+
+## Assets directories
+
+By default, the asset pipeline will process only one assets directory, `assets/`.
+You can change or add directories with the `baker/assets_dirs` setting in the
+website configuration.
+
+For each file found in an assets directory, the pipeline will either:
+
+* Ignore it, if it matches the `baker/ignore` patterns. By default, those
+  patterns include common temporary files like `.DS_Store` and `Thumbs.db`
+  files, and common source control files like `.git`, `.hg`, and `.svn`.
+
+* Process it, if it matches any of the active asset processors. The output of
+  the processing phase will be put in the output directory.
+
+* Copy it as is, if not asset processor was found. Just like for processing, the
+  relative path of the asset is preserved in the output directory.
+
+
+## Asset Processing
+
+As mentioned in the previous section, each asset file will be matched against
+available asset processors. Most processors will accept a file based on its
+extension, although some processors use other conditions. Processors have a
+priority, so for instance the `copy` processor, which accepts _all_ files, will
+be matched last.
+
+The key element however is that the PieCrust pipeline is a _multi-step_
+processing pipeline. The output of the first matched processor will be itself
+matched again against all the other processors... and so on, until no more
+processors match and the `copy` processor copies the result to the output(s)
+directory.
+
+So for instance, you if you have a LessCSS file, it will be processed like so:
+
+    foo.less    ->    foo.css    ->    foo.min.css
+
+The `.less` extension gets matched to the LessCSS processor, which outputs a
+standard `.css` file. This file gets picked up by the CleanCSS processor, which
+minifies the file, and can optionally add the `.min` suffix. There's no other
+processors that can handle a `.css` file, so the resulting `foo.min.css` is
+copied to the output directory.
+
+
+
+
+[Grunt]: http://gruntjs.com/
+[Gulp]: http://gulpjs.com/
+[procref]: {{docurl('reference/asset-processors')}}
+