fid: Listing a file's tokens
fid prints the tokens found in a given file. If two file names are passed on the command line, fid prints the tokens that are common to both files (i.e., the set intersection of the two token sets).
fid reads the ID database, therefore it accepts the ‘--file’ option, and consults the ‘IDPATH’ environment variable, as described in Reading options.
If the standard output is attached to a terminal, the printed tokens are separated by spaces. Otherwise, the tokens are printed one per line.