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 `-L
label' or `--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 `-L' option does not
affect the file names in the pr header when the `-l' or
`--paginate' option is used (see section Paginating diff Output).
Here are the first two lines of the output from `diff -C2 -Loriginal -Lmodified lao tzu':
*** original --- modified