POSIX Standard – Is the Double Dash Still Used for Long Switches?

posix

I've read several question about double dash:

Single dashes - for single-character options, but double dashes -- for words?
What does -- (double-dash) mean? (also known as “bare double dash”)

However I remember about a teacher 4 years ago telling me that -- was the posix way of dealing with long switches like --help or --color=.
Today, I'm using a lot of command where this rule is not respected at all and the best example I can came up with is find where no long switches takes a double-dash even with the very annoying AIX find.

Was my teacher wrong? or does the rule changes since (which seems unlikely)?
And finally, is there any posix rules about the length of option and - or -- ?

Best Answer

I think POSIX doesn't define long options :

Guideline 3: Each option name should be a single alphanumeric character (the alnum
character classification) from the portable character set. The -W (capital-W) option shall be reserved for vendor options.

Multi-digit options should not be allowed.

The double dash is a GNU convention.

In the POSIX definition of find the "long switches" with single dash are not part of the options, but an expression given as an operand.

Related Solutions

Does POSIX guarantee that the standard utilities are in PATH

Yes and no. In a POSIX environment, the utilities must behave as described by the specification. In practice, this means that conforming versions of the utilities must be present in $PATH. However, when running your program on a POSIX-compliant system, you may be running it in a non-conforming environment. In practice, what often happens is that the OS has a legacy mode and a POSIX mode, and is in the legacy mode by default. Worse than missing some commands, the legacy mode tends to have incompatibilities in them, such as options with different meanings.

You can retrieve a good PATH with getconf. Of course, it's tricky, as getconf in the original $PATH may not be the right one. The Application Usage for command shows a way to do it:

command -p getconf PATH

As far as I understand the specification, this is not necessary if you are running your program in a POSIX-conforming environment; and if you aren't running your program in a POSIX-conforming environment, POSIX doesn't apply. However, this application usage can be taken as a recommendation: if this doesn't work, you can feel entitled to complain to your vendor that whatever they are doing regarding the letter of the POSIX spec, they are not complying with its spirit.

Are “mostly POSIX-compliant” systems still considered POSIX systems

No. The Open Group has an actual POSIX certification process, so if an operating system hasn't been through that, it cannot be referred to as POSIX-compliant.

Best Answer

Related Solutions

Does POSIX guarantee that the standard utilities are in PATH

Are “mostly POSIX-compliant” systems still considered POSIX systems

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