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Editing: README

Description

GNU ed is a line-oriented text editor. It is used to create, display,
modify and otherwise manipulate text files, both interactively and via
shell scripts. A restricted version of ed, red, can only edit files in
the current directory and cannot execute shell commands. Ed is the
"standard" text editor in the sense that it is the original editor for
Unix, and thus widely available. For most purposes, however, it is
superseded by full-screen editors such as GNU Emacs or GNU Moe.

Extensions to and deviations from the POSIX standard are described below.

See the file INSTALL for compilation and installation instructions.

Try "ed --help" for usage instructions.

Report bugs to bug-ed@gnu.org

Ed home page: http://www.gnu.org/software/ed/ed.html

For a description of the ed algorithm, see Kernighan and Plauger's book
"Software Tools in Pascal", Addison-Wesley, 1981.

GNU ed(1) is not strictly POSIX compliant, as described in the
POSIX 1003.1-2004 document.  The following is a summary of omissions
and extensions to, and deviations from, the POSIX standard.

OMISSIONS
---------
  * Locale(3) is not supported.

EXTENSIONS
----------
  * Though GNU 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 GNU 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

* BSD commands have been implemented wherever they do not conflict with
    the POSIX standard.  The BSD-ism's included are:
      * 's' (i.e., s[1-9rgp]*) to repeat a previous substitution,
      * 'W' for appending text to an existing file,
      * 'wq' for exiting after a write, and
      * 'z' for scrolling through the buffer.

* 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 (\).

* The file commands 'E', 'e', 'r', 'W' and 'w'  process a <file>
    argument for backslash escapes; i.e., any character preceded by a
    backslash is interpreted literally. If the first 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 GNU ed.

* For SunOS ed(1) compatibility, GNU ed runs in restricted mode if invoked
    as red.  This limits editing of files in the local directory only and
    prohibits shell commands.

DEVIATIONS
----------
  * To support the BSD 's' command (see EXTENSIONS above), substitution
    patterns cannot be delimited by the digits '1' to '9' or by the
    characters 'r', 'g' and 'p'. In contrast, POSIX specifies that any
    character except space and newline can be used as a delimiter.

* Since the behavior of 'u' (undo) within a 'g' (global) command list is
    not specified by POSIX, GNU ed 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 addtion, 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 '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.

* For backwards compatibility, errors in piped scripts do not force ed
    to exit.  POSIX only specifies ed's response for input via regular
    files (including here documents) or tty's.

TESTSUITE
---------
The files in the 'testsuite' directory with extensions '.ed', '.r', and
'.err' are used for testing ed. To run the tests, configure the package
and type 'make check' from the build directory. The tests do not
exhaustively verify POSIX compliance nor do they verify correct 8-bit or
long line support.

The test file extensions have the following meanings:
.ed   Ed script - a list of ed commands.
.r    Result - the expected output after processing data via an ed
      script.
.err  Error - invalid ed commands that should generate an error.

The output of the .ed scripts is written to files with .o extension and
compared with their corresponding .r result files. The .err scripts
should exit with non-zero status without altering the contents of the
buffer.

If any test fails, the error messages look like:

*** The script u.ed exited abnormally ***
or:
	*** Output u.o of script u.ed is incorrect ***

This file is free documentation: you have unlimited permission to copy,
distribute and modify it.

The file Makefile.in is a data file used by configure to produce the
Makefile. It has the same copyright owner and permissions that configure
itself.

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