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 Comments in The GNU Emacs Manual), 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 Copying in The GNU Emacs Manual) 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 Init File in The GNU Emacs Manual). 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.