If you are comparing two files that have meaningless or uninformative names, you might want diff to show alternate names in the header of the context and unified output formats. To do this, use the --label=label option. The first time you give this option, its argument replaces the name and date of the first file in the header; the second time, its argument replaces the name and date of the second file. If you give this option more than twice, diff reports an error. The --label option does not affect the file names in the pr header when the -l or --paginate option is used (see Pagination).
Here are the first two lines of the output from ‘diff -C 2 --label=original --label=modified lao tzu’:
*** original --- modified