__linux by the difference between a horizontal (-) and a two-transverse (-) line in front of a command parameter under the Linux command.

Before we explain these differences, let's take a look at the background of Linux, which requires a thorough reading of these distinctions and a deeper understanding of Linux.

About System V and BSD styles and their relationship to Linux:

1, System V and BSD out of the AT&T lab in two different departments, SYSTEMV is a UNIX commercial standard, BSD for UNIX standardized Berkeley style.

2, since Linux is Linus Torvalds on Unix-framed systems, but still used the two main UNIX system process style, in fact, it should be said that Linus Torvalds only developed kernel, The software still comes from the GNU and GPL two organizations.

Only Slackware is currently the only BSD-style version in the Linux distribution. Others are the three renowned BSD distributions of FreeBSD, NetBSD and OpenBSD, and follow the "GPL specification. In the commercial version of UNIX and most Linux distributions, SYSTEMV-style init "may have copyright dispute issues". Linux represents almost most distributions of RedHat, Suse, MDV, Magiclinux, and Debian. UNIX is represented by AIX, IRIX, Solars, and HP-UX.

After introducing the background, let's take a look at the different ways these command parameters are used:

1, under the Linux some commands such use ls-a (parameter before a horizontal);

2, some commands such use CP--help (parameter first two transverse);

3, there are some such use of TAR-XZVF (parameters before a horizontal);

4, and some such use of tar xzvf (parameters before the transverse).

The difference between the use of commands is that we explain:

The first: The parameter is a horizontal description after the argument is the character form.

The second: The parameter is a two-transverse description of the argument followed by the word form.

The third type: The front of the parameter has a horizontal System v style.

The fourth kind: The parameter is not horizontal before the BSD style.

Other differences about System V and BSD:

During the system boot process, the INIT program is kernel in the last step, and the INIT program is executed in two styles, namely System V and BSD.
In the System V style, Init invokes the/ETC/INITTAB,BSD style invocation/ETC/RC, which are identical in that they perform a series of programs according to RunLevel.

Summary: A question brought so much background knowledge, so that there is a problem to progress.