example.
That is used in the |gzip| plugin.
   Autocommands are very powerful.  Use them with care and they will help you
avoid typing many commands.  Use them carelessly and they will cause a lot of
trouble.

Suppose you want to replace a datestamp on the end of a file every time it is
written.  First you define a function: >

	:function DateInsert()
	:  $delete
	:  read !date
	:endfunction

You want this function to be called each time, just before a buffer is written
to a file.  This will make that happen: >

	:autocmd BufWritePre *  call DateInsert()

"BufWritePre" is the event for which this autocommand is triggered: Just
before (pre) writing a buffer to a file.  The "*" is a pattern to match with
the file name.  In this case it matches all files.
   With this command enabled, when you do a ":write", Vim checks for any
matching BufWritePre autocommands and executes them, and then it
performs the ":write".
   The general form of the :autocmd command is as follows: >

	:autocmd [group] {events} {file-pattern} [++nested] {command}

The [group] name is optional.  It is used in managing and calling the commands
(more on this later).  The {events} parameter is a list of events (comma
separated) that trigger the command.
   {file-pattern} is a filename, usually with wildcards.  For example, using
"*.txt" makes the autocommand be used for all files whose name end in ".txt".
The optional [++nested] flag allows for nesting of autocommands (see below),
and finally, {command} is the command to be executed.

When adding an autocommand the already existing ones remain.  To avoid adding
the autocommand several times you should use this form: >

	:augroup updateDate
	:  autocmd!
	:  autocmd BufWritePre *  call DateInsert()
	:augroup END

This will delete any previously defined autocommand with `:autocmd!` before
defining the new one.  Groups are explained later.


EVENTS

One of the most useful events is BufReadPost.  It is triggered after a new
file is being edited.  It is commonly used to set option values.  For example,
you know that "*.gsm" files are GNU assembly language.  To get the syntax file
right, define this autocommand: >

	:autocmd BufReadPost *.gsm  set filetype=asm

If Vim is able to detect the type of file, it will set the 'filetype' option
for you.  This triggers the Filetype event.  Use this to do something when a
certain type of file is edited.  For example, to load a list of abbreviations
for text files: >

	:autocmd Filetype text  source ~/.config/nvim/abbrevs.vim

When starting to edit a new file, you could make Vim insert a skeleton: >

	:autocmd BufNewFile *.[ch]  0read ~/skeletons/skel.c

See |autocmd-events| for a complete list of events.


PATTERNS

The {file-pattern} argument can actually be a comma-separated list of file
patterns.  For example: `*.c,*.h` matches files ending in ".c" and ".h".
   The usual file wildcards can be used.  Here is a summary of the most often
used ones:

	*		Match any character any number of times
	?		Match any character once
	[abc]		Match the character a, b or c
	.		Matches a dot
	a{b,c}		Matches "ab" and "ac"

When the pattern includes a slash (/) Vim will compare directory names.
Without the slash only the last part of a file name is used.  For example,
"*.txt" matches "/home/biep/readme.txt".  The pattern "/home/biep/*" would
also match it.  But "home/foo/*.txt" wouldn't.
   When including a slash, Vim matches the pattern against both the full path
of the file ("/home/biep/readme.txt") and the relative path (e.g.,
"biep/readme.txt").

	Note:
	When working on a system that uses a backslash as file separator, such
	as MS-Windows, you still use forward slashes in autocommands.  This
	makes it easier to write the pattern, since a backslash has a special
	meaning.  It also makes the autocommands portable.


DELETING

To delete an autocommand, use the same command as what it was defined with,
but leave out the {command} at the end and use a !.  Example: >

	:autocmd! FileWritePre *

This