Run "xxeconvert" or "xxeconvert -?" to list its command-line options:

$ xxeconvert

usage: xxeconvert [Advanced option]* [Special option]*
   [-t XSLT_stylesheet_file_or_URL]?
   [-r|-ru resource_name resource_value]*
   [-p XSLT_stylesheet_param_name XSLT_stylesheet_param_value]*
   process_command_name doc_file_or_URL
   [-s|-u process_command_arg]*
...

Run "xxeconvert whatever" to list all available process commands:

$ xxeconvert foo

xxeconvert: *** ERROR *** 'foo', not a documented process command.
asm.toEclipseHelp
asm.toEpub
asm.toHTML
asm.toHTML1
asm.toHTMLHelp
asm.toPSFile
asm.toRTF
asm.toWebHelp
db5.toEclipseHelp
db5.toEpub
...

Run "xxeconvert dita.toEPUB" to print how to use the "dita.toEPUB" process command:

$ xxeconvert dita.toEPUB

xxeconvert [options] dita.toEPUB map_or_topic_file_or_URL \
  -u epub_file_or_URL

  Convert DITA map or topic map_or_topic_file_or_URL to 
  EPUB file epub_file_or_URL.

  Example:
  xxeconvert convert dita.toEPUB doc.ditamap -u out/doc.epub