M-x copyright is a skeleton inserting command, that adds a copyright notice at the point. The “by” part is taken from your environment variable $ORGANIZATION or if that isn't set you are prompted for it. If the buffer has a comment syntax (see (emacs)Comments), this is inserted as a comment.
M-x
copyright-update looks for a copyright notice in the first
copyright-limit characters of the buffer and updates
it when necessary. The current year (variable
copyright-current-year) is added to the existing
ones, in the same format as the preceding year, i.e. 1994, '94 or
94. If a dash-separated year list up to last year is found, that
is extended to current year, else the year is added separated by
a comma. Or it replaces them when this is called with a prefix
argument. If a header referring to a wrong version of the GNU
General Public License (see (emacs)Copying)
is found, that is updated too.
An interesting application for this function is to have it be
called automatically every time a file is saved. This is
accomplished by putting (add-hook 'before-save-hook
'copyright-update) into your ~/.emacs file (see (emacs)Init
File). Alternative, you can do M-x customize-variable
<RET> before-save-hook <RET>.
copyright-update is conveniently listed as an option
in the customization buffer.
The variable
copyright-query controls whether to update the
copyright or whether to ask about it. When this is
nil updating is only done with M-x
copyright-update. When this is function you
are queried whenever copyright-update is called as a
function, such as in the before-save-hook feature
mentioned above. Otherwise you are always queried.