The recommended approach when an end user wants to perform device specific activities that may involve:
XSLT is a standard for processing Extensible Markup Language (XML) data and is designed to convert one XML document into another. SLAX is an alternative to XSLT. It has a simple syntax that follows the style of C and PERL, but retains the same semantics as XSLT. Programmers who are familiar with C often find it easier to learn and use SLAX. You can easily convert SLAX scripts into XSLT and convert XSLT scripts into SLAX. Python is a commonly-used, open-source programming language with extensive standard and community libraries.
You don't need to download anything. Junos OS ships with these tools / libraries by default.