https://blog.djmnet.org/2019/08/02/why-do-long-options-start-with/

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Why Do Long Options Start with Two Dashes?

Around 1990, Richard Stallman (RMS) and I were writing the GNU C
library getopt() and he wanted to extend it to support long
(multi-character) option names for user-friendliness. He considered
Unix inferior in this regard to other operating systems such as
TOPS-20 which supported long options (that could be abbreviated). He
wanted GNU to be better than Unix while still compatible. There were
a few programs that ran on Unix systems and used long option names
starting with either - or no prefix at all, such as find, but those
syntaxes were not compatible with Unix getopt() and were parsed by
ad-hoc code.

Long options needed a prefix that wouldn't clash with the Unix
conventions, so programs could support both types of options without
ambiguity. Richard chose +, since logically if - (for a small number
mathematically) is for short options then + would be for long
options, and it's no additional typing. We created an extended
interface called getopt_long() to support specifying long options.

But when the IEEE POSIX shell and utilities standard was published in
1992, the + syntax was disallowed. GNU developers discussed what to
do over email. We considered -+ as the long options prefix, but that
was hard to type, so we settled on --, which wouldn't violate POSIX
or Unix compatibility and wasn't hard to type.

For a few months, GNU getopt() supported both + and -- to allow time
for people to transition their scripts. I'm pretty sure support for +
during that transition could be disabled by setting the environment
variable POSIX_ME_HARDER (RMS's exasperation with standards showing
there), later changed to the more polite POSIXLY_CORRECT, which also
disables recognizing options intermixed with positional arguments.

Because GNU software was popular and the solution was logical,
everyone else adopted the -- prefix and implemented variations of it
in their own argument parsers. Perl was probably one of the first.

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This entry was posted on August 2, 2019 at 4:36 pm and is filed under
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