NetBSD/bin/ed/POSIX

This version of ed(1) is not strictly POSIX compliant, as described in
the POSIX 1003.2 document.  The following is a summary of the omissions,
extensions and possible deviations from POSIX 1003.2.

OMISSIONS
---------
1) Locale(3) is not supported yet.

2) For backwards compatibility, the POSIX rule that says a range of
   addresses cannot be used where only a single address is expected has
   been relaxed.

EXTENSIONS
----------
1) BSD commands have been implemented wherever they do not conflict with
   the POSIX standard.  The BSD-ism's included are:
	i) `s' (i.e., s[rgp]*) to repeat a previous substitution,
	ii) `W' for appending text to an existing file,
	iii) `wq' for exiting after a write,
	iv) `z' for scrolling through the buffer, and
	v) BSD line addressing syntax (i.e., `^' and `%')  is recognized.

2) If crypt(3) is available, files can be read and written using DES
   encryption.  The `x' command prompts the user to enter a key used for
   encrypting/ decrypting subsequent reads and writes.  If only a newline
   is entered as the key, then encryption is disabled.  Otherwise, a key
   is read in the same manner as a password entry.  The key remains in
   effect until encryption is disabled.  For more information on the
   encryption algorithm, see the bdes(1) man page.  Encryption/decryption
   should be fully compatible with SunOS DES.

3) The POSIX interactive global commands `G' and `V' are extended to 
   support multiple commands, including `a', `i' and `c'.  The command
   format is the same as for the global commands `g' and `v', i.e., one
   command per line with each line, except for the last, ending in a
   backslash (\).

4) Though ed is not a binary editor, it can be used (if painfully) to edit
   binary files.  To assist in binary editing, when a file containing at
   least one ASCII NUL character is written, a newline is not appended if
   it did not already contain one upon reading.  For instance, to create
   a file containing a single NUL, one might use:
   $ cp /dev/null file
   $ ed file
   a
   ^@
   .
   wq
   $

5) An extension to the POSIX file commands `E', `e', `r', `W' and `w' is
   that <file> arguments are processed for backslash escapes, i.e.,  any
   character preceded by a backslash is interpreted literally.  If the
   first unescaped character of a <file> argument is a bang (!), then the
   rest of the line is interpreted as a shell command, and no escape
   processing is performed by ed.

6) The ex(1) editor's ! (bang) command syntax is supported, i.e.:
	i) commands of the form:
		(addr1,addr2) !shell-command
	   replace the addressed lines with the output of the shell-
	   command, and
	ii) commands of the form:
		[rwe] !!
	    read, write, or edit, respectively, the previous shell-command.

7) For SunOS ed(1) compatibility, ed runs in restricted mode if invoked
   as red.  This limits editing of files in the local directory only and
   prohibits shell commands.

DEVIATIONS
----------
1) Since the behavior of `u' (undo) within a `g' (global) command list is
   not specified by POSIX, it follows the behavior of the SunOS ed (this
   is the best way, I think, in that the alternatives are either too
   complicated to implement or too confusing to use):  undo forces a global
   command list to be executed only once, rather than for each line
   matching a global pattern.  In addtion, each instance of `u' within a
   global command undoes all previous commands (including undo's) in the
   command list.

2) The `m' (move) command within a `g' command list also follows the SunOS
   ed implementation: any moved lines are removed from the global command's
   `active' list.

3) If ed is invoked with a name argument prefixed by a bang, then the
   remainder of the argument is interpreted as a shell command.  To invoke
   ed on a file whose name starts with bang, prefix the name with a
   backslash.