PP - A generic Preprocessor - P is a text preprocessor designed for Pandoc (and more generally Markdown and reStructuredText).
xmllint - command line XML tool
Xidel - Xidel is a command line tool to download html/xml pages and extract data from them using CSS 3 selectors, XPath 3 expressions or pattern-matching templates.
GPP - GPP is a general-purpose preprocessor with customizable syntax, suitable for a wide range of...
XMLStarlet - XMLStarlet Command Line XML Toolkit
Filepp - filepp is a generic file preprocessor.