Using the xsltproc processor
Before you try to apply your XSLT script, you may want to validate the XML file against its DTD. To do this, use the xmllint program:
xmllint --valid --noout filename.xsl
where filename.xsl is the name of your XML file. Make sure your DTD is in the same directory and named in a <!DOCTYPE ...> declaration.
For example, if your XML document uses a DTD named trails.dtd and its root element is trails, its first line should look like this:
<!DOCTYPE trails SYSTEM "trails.dtd">
To transform a file using XSLT, use xsltproc:
xsltproc -o output.html stylesheet.xsl file.xml
where stylesheet.xsl is the XSLT stylesheet, file.xml is the XML input file, and output.html is the output file to be written.
source: http://infohost.nmt.edu/~shipman/doc/xslt/web/xsltproc-sect.html