1

man xinput describes various options used with xinput. One option is this:

--list [--short || --long || --name-only || --id-only] [device]

But I can run xinput --list or xinput list and both give the same output:

⎡ Virtual core pointer                          id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ PixArt USB Optical Mouse                  id=10   [slave  pointer  (2)]
⎜   ↳ PS/2 Mouse                                id=12   [slave  pointer  (2)]
⎜   ↳ AlpsPS/2 ALPS GlidePoint                  id=13   [slave  pointer  (2)]
⎣ Virtual core keyboard                         id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Video Bus                                 id=6    [slave  keyboard (3)]
    ↳ Power Button                              id=7    [slave  keyboard (3)]
    ↳ Sleep Button                              id=8    [slave  keyboard (3)]
    ↳ Integrated_Webcam_1.3M                    id=9    [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=11   [slave  keyboard (3)]
    ↳ Dell WMI hotkeys                          id=14   [slave  keyboard (3)]

Why is -- not needed before the list option?

(My OS is Lubuntu 13.10.)

5

Because that's how the developers wanted it.

-- and - are conventions for optional arguments.

no dashes is usually meant for operations.

In this case --list is both a operation (think sub command) and an optional argument.

See These Docs, but realize that the code writers can implement what they want. Truth is that while it is technically correct --list and list was probably implemented that way so that it was easier for more people to use.

1

The switching is completely up to the developer of the application, on how they'd like to implement it. But often times they're limited by other things out of their control, such as deciding to use a library/tool that will help them parse their command's command line argument.

For example, when developing a Bash script, 2 such tools/libraries that will facilitate this are getopt and getopts. This article does a pretty good job of showing some of the differences, titled: Bash getopt versus getopts.

Using these libraries will often times force, in a good way, the developer to implement their switching using either no dashes (i.e. list), a single dash, (i.e. (-l or -list)), or as a double dash, (--list).

Higher level languages such as Perl, Python, Ruby, C/C++ also have may of these types of libraries to choose from. This was only to explain why xinput can take either.

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