NetBSD/bin/ed/POSIX

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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.