As noted earlier, plt's command-line options can also be collected into format files, which are read by plt if named following the -f option. The names of format files, as for data files, are completely arbitrary (in this book, format files have the suffix .format, but this is only for clarity).
Format files are text files. Like data files, they may contain empty lines, and any line beginning with '#' is taken to be a comment and is ignored.
The active ingredients in format files are plt options and their arguments. In a format file, you must omit the initial hyphen ('-') from each option named. See chapter 5 for examples of figures made using command-line arguments with hyphenated options, and using a format file containing unhyphenated options.