In the manual for the ps command on Ubuntu there is this text:This version of ps accepts several kinds of options:   1   UNIX options, which may be grouped and must be preceded by a       dash.   2   BSD options, which may be grouped and must not be used with       a dash.   3   GNU long options, which are preceded by two dashes.Why is it possible that a command built in Ubuntu uses options from different operating systems? I know that the origin of Linux, UNIX and BSD are the same but they are different branches.
UNIX-, BSD-, GNU-options in Linux's ps command. Where are they from?
linux;ps;bsd;arguments