OpenGrok

This version of ed is not strictly POSIX compliant, as described in the
POSIX 1003.2 Draft 11.2 document.  BSD commands have been implemented
wherever they do not conflict with the POSIX standard.  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.

The BSD commands included are:
	1) the `s' command (i.e., s[rgp]*) to repeat a previous substitution,
	2) the `W' command for appending text to an existing file,
	3) the `wq' command for exiting after a write, and
	4) the `z' command for scrolling through the buffer.
BSD line addressing syntax (i.e., `^' and `%').  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 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.

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.

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.
--
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.