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+Copyright (C) 2023 Case Duckworth <acdw@acdw.net>
+
+Everyone is permitted to do whatever with this software, without
+limitation.  This software comes without any warranty whatsoever,
+but with two pieces of advice:
+
+- Don't hurt yourself.
+- Make good choices.
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+# vienna
+## a tiny, tasty ssg
+
+`Vienna` is my (current) Platonic Ideal of a simple and extensible static site
+generator.  I've written a couple of these over the years, and I think I've
+finally got something that I really like.  Anyway, lemme tell you how it works.
+
+## `vienna` invocation
+
+`vienna` has a similar command-line interface to `make`; that is, it runs
+commands on the files in a given folder and produces output.  It has
+command-line switches as well as subcommands.  By default, `vienna` simply
+builds the pages in the current directory into the output directory.
+
+### command-line arguments
+
+- `-r URL`: Use URL as the root url for the site.  The default is the useless
+  https://example.com/, since you really should set this either on the command
+  line, in the config file, or in an environment variable.
+- `-C DIRECTORY`: Build the site from pages in DIRECTORY, instead of the current
+  directory.
+- `-o DIRECTORY`: Build the site to DIRECTORY, instead of the default `out`.
+- `-c FILE`: Use FILE as the configuration file, instead of `.vienna.sh`.
+- `-h`: Show a usage note and exit.
+- `-q`: Disable any logging.
+
+### subcommands
+
+- `init`: Initialize a site by creating a `.vienna.sh` in the site directory.
+- `clean`: Delete the output directory and temporary files before building.
+- `preview`: Preview the website on your local machine.  By default, `vienna`
+  doesn't define a `preview` function, so you'll want to write your own.  I've
+  included one in the `.vienna.sh` made with `vienna init` to get you started.
+- `publish`: Publish the website to your production server.  By default,
+  `vienna` doesn't define a `publish` function, though I do include a sample in
+  the default `.vienna.sh` made with `vienna init`.
+
+## file layout
+
+Pretty much any SSG is a mapping from input files to output files, with various
+amounts of processing along the way.  Usually, the input files are in some
+text-ish format like markdown, the output files are in html, and processing
+includes templating, static file copying, and other such mixins.
+
+`vienna` is similar, except it uses a mostly-html input language and uses POSIX
+shell as its templating and extension language.  I chose these because they
+require the smallest number of dependencies, and because shell scripting is fun!
+[citation required]
+
+But more about the markup later.  Let's talk about the structure `vienna`
+expects your files to be in:
+
+```
+/
+/some-page.htm
+/some-other-page.htm
+[...]
+/.vienna.sh
+/.page.tmpl.htm
+/.index.tmpl.htm
+/.feed.tmpl.htm
+/.plugins/[...]
+```
+
+The content files of your site are all of the ones *not* beginning with a dot,
+while all of `vienna`'s are the ones that *are*.  In UNIX-like environments,
+this makes them "hidden," so you can focus on your content by default.  However,
+your content is not something I can talk about in this README, because you still
+have to write it!  Let's talk about `vienna`'s files next.
+
+### .vienna.sh
+
+`vienna` is a POSIX shell script.  Before it builds any pages, it reads a
+configuration file.  By default, this file is `.vienna.sh` in your site folder,
+but you can make it anything you want by passing `-c <config>` on the command
+line or by setting the `$VIENNA_CONFIG` environment variable (more on the
+command line and environment variables below).
+
+Because the configuration file is written in the same language as `vienna`
+itself, you can redefine any variable *or function* that's in `vienna`, fully
+customizing your experience.  The main knobs you'll want to turn include
+
+#### variables
+
+- `$DOMAIN`: The domain (and, well, protocol) of your published website.  Used
+when building indexes and feeds.  *Default: `https://www.example.com`*
+- `$OUTDIR`: The output directory where `vienna` will put the built site.
+*Default: `out`*
+- `$PLUGINDIR`: The directory where plugins can be found and sourced by
+`vienna`.  *Default: `.plugins`*
+- `$PAGE_TEMPLATE`: The template to use for pages.  *Default: `.page.tmpl.htm`*
+- `$INDEX_TEMPLATE`: The template to use for an index.  *Default:
+  `.index.tmpl.htm`*
+- `$FEED_TEMPLATE`: The template to use for an RSS feed.  *Default:
+  `.feed.tmpl.htm`*
+
+#### functions
+
+- `publish`: How to publish a finished site.  By default, this function does
+nothing.  `vienna init` defines a basic `publish` function in `.vienna.sh`.
+- `preview`: How to preview a site locally.  By default, this function does
+nothing.  `vienna init` defines a basic `preview` function in `.vienna.sh`.
+- `sort_items`: How to sort items when generating a list.  By default, don't
+sort files at all.
+- `index_item`: How to build each item in an index.  The default outputs `<li><a
+href=[LINK]>TITLE</a></li>`, where TITLE is the page's title and LINK is a link
+to the published page.
+- `feed_item`: How to build each item in a feed.  The default outputs an RSS
+`<item>` tag suitable for inclusion in an RSS 2.0 feed.
+- `filters`: UNIX pipes that each page is run through as it's being built.  The
+default just uses `phtml`, but in my personal site I also pipe it through
+`expand` so I can use shell expansion as well.
+
+### templates
+
+- `.page.tmpl.htm`: The template for individual pages.
+- `.index.tmpl.htm`: The template for the root index.html.
+- `.feed.tmpl.htm`: The template for the RSS feed.
+
+### plugins
+
+- `.plugins/*.sh`: Files matching this pattern will be sourced before building
+the site.  They can define new functions, export variables, or do whatever, so
+make sure you know what's in these files!
+
+## content
+
+Now for the stuff *you're* in charge of: your content.  `vienna` takes a flat-
+or no-hierarchy approach to sites.  Your site will just be one flat folder full
+of pages, though each page will be its own folder with an `index.html` for nicer
+urls.  This might not be for you, and that's okay!  You can change it
+(complicated) or use another ssg (probably easier).  It's up to you.
+
+### pages
+
+By default, files matching the pattern `*.htm` will be processed by `vienna` and
+turned into finished pages.  `.htm` was chosen because it'll be picked up as
+html in most text editors (for the format they're written in, see the **phtml**
+section below), but it's also *unfinished html* (get it?!).
+
+You can change this&mdash;you can change anything with `vienna`&mdash;but I'll
+leave that as an exercise for you to figure out.
+
+### static files
+
+Every other non-hidden file in the `vienna` folder will be copied as-is to the
+output folder.
+
+## `phtml`: *pretty much* html
+
+While lightweight markup languages like Markdown are nice (I'm using it to write
+this README, for example), I realized that for my blogging needs it's not really
+necessary.  html is *pretty much* good enough for authoring, if I'm being
+honest&mdash;it's just a little too verbose for fully-fluent drafting.
+
+Thus, `phtml` was born.  It's a function in the `vienna` source that consists of
+one sed call:
+
+```
+sed -E '
+    /./ {H;$!d}; x              # Hold lines til empty, then exchange to pattern
+    s#^[ \n\t]+([^<].*)#\1#     # Replace non-HTML paragraph with itself
+    t par; b end                # If successful, branch to :par; else :end
+    :par
+        s#([^\\])&#\1\&amp;#g   # Replace & with &amp;
+        s#([^\\])<#\1\&lt;#g    # Replace < with &lt;
+        s#([^\\])>#\1\&gt;#g    # Replace > with &gt;
+        s#\\([&<>])#\1#g        # Replace \-escaped &,<,> with raw
+        s#.*#<p>&</p>#          # Wrap the pattern space with <p> tags
+    :end                        # [:par falls through to :end]
+        s#^[ \n\t]+##           # Remove leading whitespace
+        $!a                     # Add a final newline unless last line
+'
+```
+
+To clarify the comments above: `phtml` allows a writer to leave out `<p>` tags,
+which I consider are the most annoying parts of html.  Paragraphs that don't
+begin with `<` are wrapped in `<p>` tags, and html reserved characters `<`, `>`,
+and `&` are turned into entities.
+
+You can still write html, of course&mdash;either by backslash-escaping the
+reserved characters or by starting a paragraph with an html tag (really, the
+character `<`).  Those paragraphs are passed through unprocessed.
+
+This rule may seem as though it negates the benefits of leaving out `<p>` tags.
+*After all*, you might think, *if I want to add a link or even emphasize text,
+I'll have to escape the tags or wrap the whole thing in html!*  While you'd be
+right about that, I use plaintext paragraphs enough that it's worth it.n
+
+## `expand`: templating with here-docs
+
+Here-docs are some of the most useful structures in any programming language,
+and in shell they can be especially powerful.  I first came across using
+here-docs for templating on some Github repo I've since lost, but there are many
+other projects that do something similar.  `expand` is pretty minimal, and uses
+here-docs and a little bit of escaping to provide lots of expressive power.
+
+A template that looks like this:
+
+```
+Donuts now cost $$${CURRENT_DONUT_COST}, a $$(donut_perc_delta)% 
+$$(if [ $$(donut_perc_delta) -ge 0 ]
+then echo increase
+else echo decrease
+) from last week.
+```
+
+will turn into this, given that donuts currently cost $1.99 and $1.89 last week
+(`donut_perc_delta` truncates percentages to two digits):
+
+```
+Donuts now cost $1.99, a 5%
+increase
+from last week.
+```
+
+Single `$` and <code>\`</code> characters are escaped with backslashes so they
+won't be expanded by the shell.  Two `$$` are converted to one `$`, and three
+`$$$` in a row are converted to `\$$$`, since usually you'll want the second
+pair of dollar signs to introduce a variable or function, not the first pair.
+
+Other than that, `expand` simply `eval`s the templates given on the command line
+as here-docs.  Pages to be templated are passed into the function's standard
+input, and everything just works.  It's pretty cool!
+
+### page metadata
+
+`vienna` also supports colon-separated metadata in html comments in source
+files.  I put something like the following at the tops of my pages:
+
+```
+<!--
+        title: My really cool page
+        date: 2023-01-01
+-->
+```
+
+`vienna` processes these as simple key-value pairs, accessible with the `meta`
+function.  So in templates, you can access the title with `$$(meta title)`, or
+the value of a key called `foo` with `$$(meta foo)`.
+
+`vienna` provides convenience functions `title` for the page `title` and
+`pubdate` for its `date`.
+
+## tweaking the behavior of phtml and expand (without re-writing the functions)
+
+Of course, you can always rewrite `phtml` or `expand` to suit your needs, or
+rewrite `filters` to use other processers like `markdown`, `asciidoc`, or
+whatever you desire.  However, for the "vanilla" experience, `vienna` includes a
+variable that tweaks the behavior of `phtml`: `$PHTML_OPTIONS`.
+
+`$PHTML_OPTIONS` can be one or more of the following values, separated by
+spaces:
+
+- `expand`: Run `expand` on the content after it's processed by `phtml`.
+- `entities`: Convert `&`, `<`, and `>` into html entities.
+
+The default is `expand entities`.
+
+## using plugins
+
+`vienna` also supports the use of plugins, which are shell scripts sourced
+before building the site.  Plugins are placed in `$VIENNA_PLUGINDIR`, or
+`.plugins` by default, and must end in `.sh` to be sourced.
+
+You can see the `plugins` directory of this repo for some example plugins that I
+found useful.
+
+## contributing
+
+Comments, bug reports, and merge requests are welcome!  [Send me an
+email](mailto:vienna@code.acdw.net) or [@ me on Mastodon](https://tilde.zone/@acdw).
+
+## license
+
+`vienna` is licensed under the Good Choices License.  See COPYING for details.