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authorCem Keylan <cem@ckyln.com>2021-07-14 17:07:06 +0300
committerCem Keylan <cem@ckyln.com>2021-07-14 17:07:06 +0300
commitd7f8dce37ecea2fa24883b58a8bbd5f25fb69221 (patch)
tree34f8326573d65b5cf5704bf4c9fb4c3e36f106ec /bin/ed/POSIX
parent9270286d5a675a4924d94adaca4099441a3cae5a (diff)
downloadotools-d7f8dce37ecea2fa24883b58a8bbd5f25fb69221.tar.gz
ed: port to otools
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+$OpenBSD: POSIX,v 1.8 2014/05/24 01:35:55 daniel Exp $
+$NetBSD: POSIX,v 1.9 1995/03/21 09:04:32 cgd Exp $
+
+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.
+
+3) To support the BSD `s' command (see extension [1] below),
+ substitution patterns cannot be delimited by numbers or the characters
+ `r', `g' and `p'. In contrast, POSIX specifies any character except
+ space or newline can be used as a delimiter.
+
+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[n][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) 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 (\).
+
+3) 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.
+
+DEVIATIONS
+----------
+1) Though ed is not a stream editor, it can be used 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. In particular, reading /dev/null
+ prior to writing prevents appending a newline to a binary file.
+
+ For example, to create a file with ed containing a single NUL character:
+ $ ed file
+ a
+ ^@
+ .
+ r /dev/null
+ wq
+
+ Similarly, to remove a newline from the end of binary `file':
+ $ ed file
+ r /dev/null
+ wq
+
+2) 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:
+ undo forces a global command list to be executed only once, rather than
+ for each line matching a global pattern. In addition, each instance of
+ `u' within a global command undoes all previous commands (including
+ undo's) in the command list. This seems the best way, since the
+ alternatives are either too complicated to implement or too confusing
+ to use.
+
+ The global/undo combination is useful for masking errors that
+ would otherwise cause a script to fail. For instance, an ed script
+ to remove any occurrences of either `censor1' or `censor2' might be
+ written as:
+ ed - file <<EOF
+ 1g/.*/u\
+ ,s/censor1//g\
+ ,s/censor2//g
+ ...
+
+3) 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.
+
+4) 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.