While working on your site, you can run the command docpad watch
.
»To render standalone files with DocPad programatically (will output to stdout)«
docpad render filePath
»E.g. To render a markdown file and save the result to an output file, we would use:«
docpad render inputMarkdownFile.html.md > outputMarkdownFile.html
»To just watch your website for changes and re-generate whenever a change is made, use:« docpad watch
Source: http://docpad.org/docs/cli