6.20.1.2 What are options for?
Options are used to provide extra information to tune or customize the execution of a
program. In case it wasn't clear, options should be optional. A program should be able
to run just fine with no options whatsoever. (Pick a random program from the Unix or GNU toolsets. Can it run without any options
at all and still make sense? The only exceptions I can think of are find,
tar, and dd--all of which are mutant oddballs
that have been rightly criticized for their non-standard syntax and confusing interfaces.)
Lots of people want their programs to have ``required options''. Think about it. If it's
required, then it's not optional! If there is a piece of information that your program
absolutely requires in order to run successfully, that's what positional arguments are for.
(However, if you insist on adding ``required options'' to your programs, look in ``Extending
Examples'' (section 6.20.5) for two ways
of implementing them with optparse.)
Consider the humble cp utility, for copying files. It doesn't make
much sense to try to copy files without supplying a destination and at least one source.
Hence, cp fails if you run it with no arguments. However, it has a
flexible, useful syntax that does not rely on options at all:
$ cp SOURCE DEST
$ cp SOURCE ... DEST-DIR
You can get pretty far with just that. Most cp implementations
provide a bunch of options to tweak exactly how the files are copied: you can preserve mode
and modification time, avoid following symlinks, ask before clobbering existing files, etc.
But none of this distracts from the core mission of cp, which is to
copy one file to another, or N files to another directory.
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