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xmllint - command line XML tool
Perl - Highly capable, feature-rich programming language with over 26 years of development
GCC C Preprocessor (cpp) - Top (The C Preprocessor)
TXR - Pragmatic, convenient data munging language.
PP - A generic Preprocessor - P is a text preprocessor designed for Pandoc (and more generally Markdown and reStructuredText).
AWK - Linux users can perform many types of searching, replacing and report generating tasks by using awk, grep and sed commands.