This is the command idxmerge that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator
idxmerge - merge fweb-produced index files.
idxmerge -ndex-fle file1.idx...
idxmerge merges index files produced by the invocation of fweave with option -XI.
Further documentation can be obtained from texinfo, available online through emacs' info
browser (menu item fweb ), or in HTML format.
Use idxmerge online using onworks.net services