markdown.bash is a Markdown interpreter using only traditional Unix tools. Specifically, it only uses Bash, Sed, Grep, and Cut (in one small instance).
Good question. There already exist Markdown implementations in a variety of languages. Plus, the original Markdown was written in Perl which exists on virtually all Unix machines. So I didn't write it for any practical reason. Really I just wanted to see how much of it I could re-engineer in a single Bash script using mostly Sed for the transformations.
You use it just like any other Unix program - by either passing files to it or piping input into it.
sh markdown.sh file1 file2 file3 > output.html
echo "# heading1\n\nparagraph" | sh markdown.sh
sh markdown.sh samples/test.md
By my own rough estimate, markdown.bash implements about 95% of the Markdown language. Still there are some areas where it doesn't.
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It doesn't convert E-mail addresses to a mix of decimal and hex entity-encoding. I really did not know a good, canonical way to do this in Unix/Linux. Suggestions are welcome.
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It processes Markdown inside block-level HTML. According to the original spec: Note that Markdown formatting syntax is not processed within block-level HTML tags. E.g., you can’t use Markdown-style emphasis inside an HTML block. markdown.bash does process Markdown syntax within block-level HTML. I couldn't think of a good way to implement this exactly like the spec.
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Due to the line-by-line processing nature of Sed, I recommend always putting hard breaks (\n\n) between block-level elements (lists, paragraphs, etc). markdown.bash does a lot less implicit processing of elements separated by only one break (\n) than the Perl version does.
Before starting this project I had only a cursory understanding of Sed. I'm still not an expert, but I do know a lot more now. A couple of web resources were especially helpful.