NetBSD/bin/ed/doc/extensions

This version of ed is not strictly POSIX compliant, as described in the
POSIX 1003.2 Draft 11.2 document (see the file `ed-1003.2').  BSD commands
have been implemented wherever they do not conflict with the POSIX
standard.  In addtion, the POSIX rule that says a range of addresses
cannot be used where only a single address is expected has been relaxed
(see the file `legal-addrs').

The BSD which have been added include the BSD `W' command for appending
text to an existing file, the BSD `s' command (i.e., s[rgp]*) to repeat
a previous substitution, the BSD `z' command for scrolling through the
buffer, and the BSD `wq' command for exiting after write.  The BSD line
addressing syntax (i.e., `^' and `%' - see the file `legal.addrs') is also
recognized.

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 (\).

If crypt is available, files can be read and written using DES encryption.
The `x' command prompts the user to enter a key 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 with echoing turned
off until a newline is entered.  For more information on the encryption
algorithm, see the bdes(1) man page.  Encryption/decryption should be
fully compatible with SunOS DES.

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.  A trailing
backslash is ignored.  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.  This rule does
not apply to the 'f' command (described below).

While the default file name cannot be set to a shell command (i.e.,
!<shell-cmd>) via any of the `r', `w', and `e' commands, POSIX evidently
does not preclude using the `f' command for this purpose.  Upon reading
or writing the default file when its name begins with a bang (!), ed
interprets the rest of the line as a shell command and attempts to execute
it.  Escape processing is not performed in this case.  The `f' command
can be used in this way as a simple macro function.  For example, after
setting the default file name to `!echo hello, world', the command `.r'
inserts the line `hello world' after the current line.  The `f' command
with no arguments prints the default unescaped file name.

--
The following commands are neither part of POSIX 1003.2 D11/2 nor are
they supported in this version of ed. 

The vi command: (addr1,addr2) !<shell-cmd> which replaces a range of
lines with the output of a shell command is not supported.

The vi command: [rwe] !!, where !! is replaced by the previous
!<shell-cmd> is not supported.