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POSIX revision 1.2 
      1 This version of ed is not strictly POSIX compliant, as described in the
      2 POSIX 1003.2 Draft 11.2 document.  BSD commands have been implemented
      3 wherever they do not conflict with the POSIX standard.  For backwards
      4 compatibility, the POSIX rule that says a range of addresses cannot be
      5 used where only a single address is expected has been relaxed.
      6 
      7 The 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.
     12 BSD line addressing syntax (i.e., `^' and `%').  is also recognized.
     13 
     14 The POSIX interactive global commands `G' and `V' are extended to support
     15 multiple commands, including `a', `i' and `c'.  The command format is the
     16 same as for the global commands `g' and `v', i.e., one command per line
     17 with each line, except for the last, ending in a backslash (\).
     18 
     19 If crypt is available, files can be read and written using DES encryption.
     20 The `x' command prompts the user to enter a key used for encrypting/
     21 decrypting subsequent reads and writes.  If only a newline is entered as
     22 the key, then encryption is disabled.  Otherwise, a key is read in the
     23 same manner as a password entry.  The key remains in effect until
     24 encryption is disabled.  For more information on the encryption algorithm,
     25 see the bdes(1) man page.  Encryption/decryption should be fully compatible
     26 with SunOS DES.
     27 
     28 An 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
     30 preceded by a backslash is interpreted literally.  If the first unescaped
     31 character of a <file> argument is a bang (!), then the rest of the line
     32 is interpreted as a shell command, and no escape processing is performed
     33 by ed.
     34 
     35 The 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 
     40 If ed is invoked with a name argument prefixed by a bang, then the
     41 remainder of the argument is interpreted as a shell command.  To invoke
     42 ed on a file whose name starts with bang, prefix the name with a backslash.
     43