POSIX revision 49 
1This version of ed is not strictly POSIX compliant, as described in the
2POSIX 1003.2 Draft 11.2 document.  BSD commands have been implemented
3wherever they do not conflict with the POSIX standard.  For backwards
4compatibility, the POSIX rule that says a range of addresses cannot be
5used where only a single address is expected has been relaxed.
6
7The BSD commands included are:
8	1) `s' (i.e., s[rgp]*) to repeat a previous substitution,
9	2) `W' for appending text to an existing file,
10	3) `wq' for exiting after a write, and
11	4) `z' for scrolling through the buffer.
12BSD line addressing syntax (i.e., `^' and `%').  is also recognized.
13
14The POSIX interactive global commands `G' and `V' are extended to support
15multiple commands, including `a', `i' and `c'.  The command format is the
16same as for the global commands `g' and `v', i.e., one command per line
17with each line, except for the last, ending in a backslash (\).
18
19If crypt is available, files can be read and written using DES encryption.
20The `x' command prompts the user to enter a key used for encrypting/
21decrypting subsequent reads and writes.  If only a newline is entered as
22the key, then encryption is disabled.  Otherwise, a key is read in the
23same manner as a password entry.  The key remains in effect until
24encryption is disabled.  For more information on the encryption algorithm,
25see the bdes(1) man page.  Encryption/decryption should be fully compatible
26with SunOS DES.
27
28An extension to the POSIX file commands `E', `e', `r', `W' and `w' is that
29<file> arguments are processed for backslash escapes, i.e.,  any character
30preceded by a backslash is interpreted literally.  If the first unescaped
31character of a <file> argument is a bang (!), then the rest of the line
32is interpreted as a shell command, and no escape processing is performed
33by ed.
34
35The vi editor's bang command syntax is supported, i.e.,
36(addr1,addr2) !<shell-cmd> replaces the addressed lines with the output of 
37	the command <shell-cmd>.
38[rwe] !! reads/writes/edits the previous !<shell-cmd>.
39
40If ed is invoked with a name argument prefixed by a bang, then the
41remainder of the argument is interpreted as a shell command.  To invoke
42ed on a file whose name starts with bang, prefix the name with a backslash.
43
44ed runs in restricted mode if invoked as red.  This limits editing of
45files in the local directory only and prohibits !<shell-cmd> commands.
46
47Though ed is not a binary editor, it can be used (if painfully) to edit
48binary files.  To assist in binary editing, when a file containing at
49least one ASCII NUL character is written, a newline is not appended
50if it did not already contain one upon reading.
51
52Since the behavior of `u' (undo) within a `g' (global) command list is
53not specified by POSIX D11/2, it follows the behavior of the SunOS ed
54(this is the best way, I think, in that the alternatives are either too
55complicated to implement or too confusing to use):  undo forces a global
56command list to be executed only once, rather than for each line matching
57a global pattern.  In addtion, each instance of `u' within a global command
58undoes all previous commands (including undo's) in the command list.
59
60The `m' (move) command within a `g' command list also follows the SunOS
61ed implementation: any moved lines are removed from the global command's
62`active' list.
63