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PROGRAM:

NAME


ed — edit text

SYNOPSIS


ed [−p string] [−s] [file]

DESCRIPTION


The ed utility is a line-oriented text editor that uses two modes: command mode and input
mode. In command mode the input characters shall be interpreted as commands, and in input
mode they shall be interpreted as text. See the EXTENDED DESCRIPTION section.

If an operand is '−', the results are unspecified.

OPTIONS


The ed utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section 12.2,
Utility Syntax Guidelines, except for the unspecified usage of '−'.

The following options shall be supported:

−p string Use string as the prompt string when in command mode. By default, there shall be
no prompt string.

−s Suppress the writing of byte counts by e, E, r, and w commands and of the '!'
prompt after a !command.

OPERANDS


The following operand shall be supported:

file If the file argument is given, ed shall simulate an e command on the file named
by the pathname, file, before accepting commands from the standard input.

STDIN


The standard input shall be a text file consisting of commands, as described in the
EXTENDED DESCRIPTION section.

INPUT FILES


The input files shall be text files.

ENVIRONMENT VARIABLES


The following environment variables shall affect the execution of ed:

HOME Determine the pathname of the user's home directory.

LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of POSIX.1‐2008, Section 8.2,
Internationalization Variables for the precedence of internationalization
variables used to determine the values of locale categories.)

LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.

LC_COLLATE
Determine the locale for the behavior of ranges, equivalence classes, and multi-
character collating elements within regular expressions.

LC_CTYPE Determine the locale for the interpretation of sequences of bytes of text data
as characters (for example, single-byte as opposed to multi-byte characters in
arguments and input files) and the behavior of character classes within regular
expressions.

LC_MESSAGES
Determine the locale that should be used to affect the format and contents of
diagnostic messages written to standard error and informative messages written
to standard output.

NLSPATH Determine the location of message catalogs for the processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS


The ed utility shall take the standard action for all signals (see the ASYNCHRONOUS EVENTS
section in Section 1.4, Utility Description Defaults) with the following exceptions:

SIGINT The ed utility shall interrupt its current activity, write the string "?\n" to
standard output, and return to command mode (see the EXTENDED DESCRIPTION
section).

SIGHUP If the buffer is not empty and has changed since the last write, the ed utility
shall attempt to write a copy of the buffer in a file. First, the file named
ed.hup in the current directory shall be used; if that fails, the file named
ed.hup in the directory named by the HOME environment variable shall be used. In
any case, the ed utility shall exit without writing the file to the currently
remembered pathname and without returning to command mode.

SIGQUIT The ed utility shall ignore this event.

STDOUT


Various editing commands and the prompting feature (see −p) write to standard output, as
described in the EXTENDED DESCRIPTION section.

STDERR


The standard error shall be used only for diagnostic messages.

OUTPUT FILES


The output files shall be text files whose formats are dependent on the editing commands
given.

EXTENDED DESCRIPTION


The ed utility shall operate on a copy of the file it is editing; changes made to the copy
shall have no effect on the file until a w (write) command is given. The copy of the text
is called the buffer.

Commands to ed have a simple and regular structure: zero, one, or two addresses followed
by a single-character command, possibly followed by parameters to that command. These
addresses specify one or more lines in the buffer. Every command that requires addresses
has default addresses, so that the addresses very often can be omitted. If the −p option
is specified, the prompt string shall be written to standard output before each command is
read.

In general, only one command can appear on a line. Certain commands allow text to be
input. This text is placed in the appropriate place in the buffer. While ed is accepting
text, it is said to be in input mode. In this mode, no commands shall be recognized; all
input is merely collected. Input mode is terminated by entering a line consisting of two
characters: a <period> ('.') followed by a <newline>. This line is not considered part
of the input text.

Regular Expressions in ed
The ed utility shall support basic regular expressions, as described in the Base
Definitions volume of POSIX.1‐2008, Section 9.3, Basic Regular Expressions. Since regular
expressions in ed are always matched against single lines (excluding the terminating
<newline> characters), never against any larger section of text, there is no way for a
regular expression to match a <newline>.

A null RE shall be equivalent to the last RE encountered.

Regular expressions are used in addresses to specify lines, and in some commands (for
example, the s substitute command) to specify portions of a line to be substituted.

Addresses in ed
Addressing in ed relates to the current line. Generally, the current line is the last line
affected by a command. The current line number is the address of the current line. If the
edit buffer is not empty, the initial value for the current line shall be the last line in
the edit buffer; otherwise, zero.

Addresses shall be constructed as follows:

1. The <period> character ('.') shall address the current line.

2. The <dollar-sign> character ('$') shall address the last line of the edit buffer.

3. The positive decimal number n shall address the nth line of the edit buffer.

4. The <apostrophe>-x character pair ("'x") shall address the line marked with the mark
name character x, which shall be a lowercase letter from the portable character set.
It shall be an error if the character has not been set to mark a line or if the line
that was marked is not currently present in the edit buffer.

5. A BRE enclosed by <slash> characters ('/') shall address the first line found by
searching forwards from the line following the current line toward the end of the edit
buffer and stopping at the first line for which the line excluding the terminating
<newline> matches the BRE. The BRE consisting of a null BRE delimited by a pair of
<slash> characters shall address the next line for which the line excluding the
terminating <newline> matches the last BRE encountered. In addition, the second
<slash> can be omitted at the end of a command line. Within the BRE, a
<backslash>-<slash> pair ("\/") shall represent a literal <slash> instead of the BRE
delimiter. If necessary, the search shall wrap around to the beginning of the buffer
and continue up to and including the current line, so that the entire buffer is
searched.

6. A BRE enclosed by <question-mark> characters ('?') shall address the first line found
by searching backwards from the line preceding the current line toward the beginning
of the edit buffer and stopping at the first line for which the line excluding the
terminating <newline> matches the BRE. The BRE consisting of a null BRE delimited by a
pair of <question-mark> characters ("??") shall address the previous line for which
the line excluding the terminating <newline> matches the last BRE encountered. In
addition, the second <question-mark> can be omitted at the end of a command line.
Within the BRE, a <backslash>-<question-mark> pair ("\?") shall represent a literal
<question-mark> instead of the BRE delimiter. If necessary, the search shall wrap
around to the end of the buffer and continue up to and including the current line, so
that the entire buffer is searched.

7. A <plus-sign> ('+') or <hyphen> character ('−') followed by a decimal number shall
address the current line plus or minus the number. A <plus-sign> or <hyphen> character
not followed by a decimal number shall address the current line plus or minus 1.

Addresses can be followed by zero or more address offsets, optionally <blank>-separated.
Address offsets are constructed as follows:

* A <plus-sign> or <hyphen> character followed by a decimal number shall add or
subtract, respectively, the indicated number of lines to or from the address. A <plus-
sign> or <hyphen> character not followed by a decimal number shall add or subtract 1
to or from the address.

* A decimal number shall add the indicated number of lines to the address.

It shall not be an error for an intermediate address value to be less than zero or greater
than the last line in the edit buffer. It shall be an error for the final address value to
be less than zero or greater than the last line in the edit buffer. It shall be an error
if a search for a BRE fails to find a matching line.

Commands accept zero, one, or two addresses. If more than the required number of addresses
are provided to a command that requires zero addresses, it shall be an error. Otherwise,
if more than the required number of addresses are provided to a command, the addresses
specified first shall be evaluated and then discarded until the maximum number of valid
addresses remain, for the specified command.

Addresses shall be separated from each other by a <comma> (',') or <semicolon> character
(';'). In the case of a <semicolon> separator, the current line ('.') shall be set to
the first address, and only then will the second address be calculated. This feature can
be used to determine the starting line for forwards and backwards searches; see rules 5.
and 6.

Addresses can be omitted on either side of the <comma> or <semicolon> separator, in which
case the resulting address pairs shall be as follows:

┌──────────┬─────────────┐
SpecifiedResulting
├──────────┼─────────────┤
│, │ 1 , $ │
│, addr │ 1 , addr │
│addr , │ addr , addr │
│; │ . ; $ │
│; addr │ . ; addr │
│addr ; │ addr ; addr │
└──────────┴─────────────┘
Any <blank> characters included between addresses, address separators, or address offsets
shall be ignored.

Commands in ed
In the following list of ed commands, the default addresses are shown in parentheses. The
number of addresses shown in the default shall be the number expected by the command. The
parentheses are not part of the address; they show that the given addresses are the
default.

It is generally invalid for more than one command to appear on a line. However, any
command (except e, E, f, q, Q, r, w, and !) can be suffixed by the letter l, n, or p; in
which case, except for the l, n, and p commands, the command shall be executed and then
the new current line shall be written as described below under the l, n, and p commands.
When an l, n, or p suffix is used with an l, n, or p command, the command shall write to
standard output as described below, but it is unspecified whether the suffix writes the
current line again in the requested format or whether the suffix has no effect. For
example, the pl command (base p command with an l suffix) shall either write just the
current line or write it twice—once as specified for p and once as specified for l. Also,
the g, G, v, and V commands shall take a command as a parameter.

Each address component can be preceded by zero or more <blank> characters. The command
letter can be preceded by zero or more <blank> characters. If a suffix letter (l, n, or p)
is given, the application shall ensure that it immediately follows the command.

The e, E, f, r, and w commands shall take an optional file parameter, separated from the
command letter by one or more <blank> characters.

If changes have been made in the buffer since the last w command that wrote the entire
buffer, ed shall warn the user if an attempt is made to destroy the editor buffer via the
e or q commands. The ed utility shall write the string:

"?\n"

(followed by an explanatory message if help mode has been enabled via the H command) to
standard output and shall continue in command mode with the current line number unchanged.
If the e or q command is repeated with no intervening command, it shall take effect.

If a terminal disconnect (see the Base Definitions volume of POSIX.1‐2008, Chapter 11,
General Terminal Interface, Modem Disconnect and Closing a Device Terminal), is detected:

* If accompanied by a SIGHUP signal, the ed utility shall operate as described in the
ASYNCHRONOUS EVENTS section for a SIGHUP signal.

* If not accompanied by a SIGHUP signal, the ed utility shall act as if an end-of-file
had been detected on standard input.

If an end-of-file is detected on standard input:

* If the ed utility is in input mode, ed shall terminate input mode and return to
command mode. It is unspecified if any partially entered lines (that is, input text
without a terminating <newline>) are discarded from the input text.

* If the ed utility is in command mode, it shall act as if a q command had been entered.

If the closing delimiter of an RE or of a replacement string (for example, '/') in a g, G,
s, v, or V command would be the last character before a <newline>, that delimiter can be
omitted, in which case the addressed line shall be written. For example, the following
pairs of commands are equivalent:

s/s1/s2 s/s1/s2/p
g/s1 g/s1/p
?s1 ?s1?

If an invalid command is entered, ed shall write the string:

"?\n"

(followed by an explanatory message if help mode has been enabled via the H command) to
standard output and shall continue in command mode with the current line number unchanged.

Append Command
Synopsis:
(.)a
<text>
.

The a command shall read the given text and append it after the addressed line; the
current line number shall become the address of the last inserted line or, if there were
none, the addressed line. Address 0 shall be valid for this command; it shall cause the
appended text to be placed at the beginning of the buffer.

Change Command
Synopsis:
(.,.)c
<text>
.

The c command shall delete the addressed lines, then accept input text that replaces these
lines; the current line shall be set to the address of the last line input; or, if there
were none, at the line after the last line deleted; if the lines deleted were originally
at the end of the buffer, the current line number shall be set to the address of the new
last line; if no lines remain in the buffer, the current line number shall be set to zero.
Address 0 shall be valid for this command; it shall be interpreted as if address 1 were
specified.

Delete Command
Synopsis:
(.,.)d

The d command shall delete the addressed lines from the buffer. The address of the line
after the last line deleted shall become the current line number; if the lines deleted
were originally at the end of the buffer, the current line number shall be set to the
address of the new last line; if no lines remain in the buffer, the current line number
shall be set to zero.

Edit Command
Synopsis:
e [file]

The e command shall delete the entire contents of the buffer and then read in the file
named by the pathname file. The current line number shall be set to the address of the
last line of the buffer. If no pathname is given, the currently remembered pathname, if
any, shall be used (see the f command). The number of bytes read shall be written to
standard output, unless the −s option was specified, in the following format:

"%d\n", <number of bytes read>

The name file shall be remembered for possible use as a default pathname in subsequent e,
E, r, and w commands. If file is replaced by '!', the rest of the line shall be taken to
be a shell command line whose output is to be read. Such a shell command line shall not be
remembered as the current file. All marks shall be discarded upon the completion of a
successful e command. If the buffer has changed since the last time the entire buffer was
written, the user shall be warned, as described previously.

Edit Without Checking Command
Synopsis:
E [file]

The E command shall possess all properties and restrictions of the e command except that
the editor shall not check to see whether any changes have been made to the buffer since
the last w command.

Filename Command
Synopsis:
f [file]

If file is given, the f command shall change the currently remembered pathname to file;
whether the name is changed or not, it shall then write the (possibly new) currently
remembered pathname to the standard output in the following format:

"%s\n", <pathname>

The current line number shall be unchanged.

Global Command
Synopsis:
(1,$)g/RE/command list

In the g command, the first step shall be to mark every line for which the line excluding
the terminating <newline> matches the given RE. Then, going sequentially from the
beginning of the file to the end of the file, the given command list shall be executed for
each marked line, with the current line number set to the address of that line. Any line
modified by the command list shall be unmarked. When the g command completes, the current
line number shall have the value assigned by the last command in the command list. If
there were no matching lines, the current line number shall not be changed. A single
command or the first of a list of commands shall appear on the same line as the global
command. All lines of a multi-line list except the last line shall be ended with a
<backslash> preceding the terminating <newline>; the a, i, and c commands and associated
input are permitted. The '.' terminating input mode can be omitted if it would be the
last line of the command list. An empty command list shall be equivalent to the p command.
The use of the g, G, v, V, and ! commands in the command list produces undefined results.
Any character other than <space> or <newline> can be used instead of a <slash> to delimit
the RE. Within the RE, the RE delimiter itself can be used as a literal character if it is
preceded by a <backslash>.

Interactive Global Command
Synopsis:
(1,$)G/RE/

In the G command, the first step shall be to mark every line for which the line excluding
the terminating <newline> matches the given RE. Then, for every such line, that line shall
be written, the current line number shall be set to the address of that line, and any one
command (other than one of the a, c, i, g, G, v, and V commands) shall be read and
executed. A <newline> shall act as a null command (causing no action to be taken on the
current line); an '&' shall cause the re-execution of the most recent non-null command
executed within the current invocation of G. Note that the commands input as part of the
execution of the G command can address and affect any lines in the buffer. Any line
modified by the command shall be unmarked. The final value of the current line number
shall be the value set by the last command successfully executed. (Note that the last
command successfully executed shall be the G command itself if a command fails or the null
command is specified.) If there were no matching lines, the current line number shall not
be changed. The G command can be terminated by a SIGINT signal. Any character other than
<space> or <newline> can be used instead of a <slash> to delimit the RE and the
replacement. Within the RE, the RE delimiter itself can be used as a literal character if
it is preceded by a <backslash>.

Help Command
Synopsis:
h

The h command shall write a short message to standard output that explains the reason for
the most recent '?' notification. The current line number shall be unchanged.

Help-Mode Command
Synopsis:
H

The H command shall cause ed to enter a mode in which help messages (see the h command)
shall be written to standard output for all subsequent '?' notifications. The H command
alternately shall turn this mode on and off; it is initially off. If the help-mode is
being turned on, the H command also explains the previous '?' notification, if there was
one. The current line number shall be unchanged.

Insert Command
Synopsis:
(.)i
<text>
.

The i command shall insert the given text before the addressed line; the current line is
set to the last inserted line or, if there was none, to the addressed line. This command
differs from the a command only in the placement of the input text. Address 0 shall be
valid for this command; it shall be interpreted as if address 1 were specified.

Join Command
Synopsis:
(.,.+1)j

The j command shall join contiguous lines by removing the appropriate <newline>
characters. If exactly one address is given, this command shall do nothing. If lines are
joined, the current line number shall be set to the address of the joined line; otherwise,
the current line number shall be unchanged.

Mark Command
Synopsis:
(.)kx

The k command shall mark the addressed line with name x, which the application shall
ensure is a lowercase letter from the portable character set. The address "'x" shall then
refer to this line; the current line number shall be unchanged.

List Command
Synopsis:
(.,.)l

The l command shall write to standard output the addressed lines in a visually unambiguous
form. The characters listed in the Base Definitions volume of POSIX.1‐2008, Table 5-1,
Escape Sequences and Associated Actions ('\\', '\a', '\b', '\f', '\r', '\t', '\v') shall
be written as the corresponding escape sequence; the '\n' in that table is not applicable.
Non-printable characters not in the table shall be written as one three-digit octal number
(with a preceding <backslash> character) for each byte in the character (most significant
byte first).

Long lines shall be folded, with the point of folding indicated by <newline> preceded by a
<backslash>; the length at which folding occurs is unspecified, but should be appropriate
for the output device. The end of each line shall be marked with a '$', and '$' characters
within the text shall be written with a preceding <backslash>. An l command can be
appended to any other command other than e, E, f, q, Q, r, w, or !. The current line
number shall be set to the address of the last line written.

Move Command
Synopsis:
(.,.)maddress

The m command shall reposition the addressed lines after the line addressed by address.
Address 0 shall be valid for address and cause the addressed lines to be moved to the
beginning of the buffer. It shall be an error if address address falls within the range of
moved lines. The current line number shall be set to the address of the last line moved.

Number Command
Synopsis:
(.,.)n

The n command shall write to standard output the addressed lines, preceding each line by
its line number and a <tab>; the current line number shall be set to the address of the
last line written. The n command can be appended to any command other than e, E, f, q, Q,
r, w, or !.

Print Command
Synopsis:
(.,.)p

The p command shall write to standard output the addressed lines; the current line number
shall be set to the address of the last line written. The p command can be appended to any
command other than e, E, f, q, Q, r, w, or !.

Prompt Command
Synopsis:
P

The P command shall cause ed to prompt with an <asterisk> ('*') (or string, if −p is
specified) for all subsequent commands. The P command alternatively shall turn this mode
on and off; it shall be initially on if the −p option is specified; otherwise, off. The
current line number shall be unchanged.

Quit Command
Synopsis:
q

The q command shall cause ed to exit. If the buffer has changed since the last time the
entire buffer was written, the user shall be warned, as described previously.

Quit Without Checking Command
Synopsis:
Q

The Q command shall cause ed to exit without checking whether changes have been made in
the buffer since the last w command.

Read Command
Synopsis:
($)r [file]

The r command shall read in the file named by the pathname file and append it after the
addressed line. If no file argument is given, the currently remembered pathname, if any,
shall be used (see the e and f commands). The currently remembered pathname shall not be
changed unless there is no remembered pathname. Address 0 shall be valid for r and shall
cause the file to be read at the beginning of the buffer. If the read is successful, and
−s was not specified, the number of bytes read shall be written to standard output in the
following format:

"%d\n", <number of bytes read>

The current line number shall be set to the address of the last line read in. If file is
replaced by '!', the rest of the line shall be taken to be a shell command line whose
output is to be read. Such a shell command line shall not be remembered as the current
pathname.

Substitute Command
Synopsis:
(.,.)s/RE/replacement/flags

The s command shall search each addressed line for an occurrence of the specified RE and
replace either the first or all (non-overlapped) matched strings with the replacement; see
the following description of the g suffix. It is an error if the substitution fails on
every addressed line. Any character other than <space> or <newline> can be used instead of
a <slash> to delimit the RE and the replacement. Within the RE, the RE delimiter itself
can be used as a literal character if it is preceded by a <backslash>. The current line
shall be set to the address of the last line on which a substitution occurred.

An <ampersand> ('&') appearing in the replacement shall be replaced by the string matching
the RE on the current line. The special meaning of '&' in this context can be suppressed
by preceding it by <backslash>. As a more general feature, the characters '\n', where n
is a digit, shall be replaced by the text matched by the corresponding back-reference
expression. If the corresponding back-reference expression does not match, then the
characters '\n' shall be replaced by the empty string. When the character '%' is the only
character in the replacement, the replacement used in the most recent substitute command
shall be used as the replacement in the current substitute command; if there was no
previous substitute command, the use of '%' in this manner shall be an error. The '%'
shall lose its special meaning when it is in a replacement string of more than one
character or is preceded by a <backslash>. For each <backslash> encountered in scanning
replacement from beginning to end, the following character shall lose its special meaning
(if any). It is unspecified what special meaning is given to any character other than
<backslash>, '&', '%', or digits.

A line can be split by substituting a <newline> into it. The application shall ensure it
escapes the <newline> in the replacement by preceding it by <backslash>. Such
substitution cannot be done as part of a g or v command list. The current line number
shall be set to the address of the last line on which a substitution is performed. If no
substitution is performed, the current line number shall be unchanged. If a line is split,
a substitution shall be considered to have been performed on each of the new lines for the
purpose of determining the new current line number. A substitution shall be considered to
have been performed even if the replacement string is identical to the string that it
replaces.

The application shall ensure that the value of flags is zero or more of:

count Substitute for the countth occurrence only of the RE found on each addressed line.

g Globally substitute for all non-overlapping instances of the RE rather than just
the first one. If both g and count are specified, the results are unspecified.

l Write to standard output the final line in which a substitution was made. The line
shall be written in the format specified for the l command.

n Write to standard output the final line in which a substitution was made. The line
shall be written in the format specified for the n command.

p Write to standard output the final line in which a substitution was made. The line
shall be written in the format specified for the p command.

Copy Command
Synopsis:
(.,.)taddress

The t command shall be equivalent to the m command, except that a copy of the addressed
lines shall be placed after address address (which can be 0); the current line number
shall be set to the address of the last line added.

Undo Command
Synopsis:
u

The u command shall nullify the effect of the most recent command that modified anything
in the buffer, namely the most recent a, c, d, g, i, j, m, r, s, t, u, v, G, or V command.
All changes made to the buffer by a g, G, v, or V global command shall be undone as a
single change; if no changes were made by the global command (such as with g/RE/p), the u
command shall have no effect. The current line number shall be set to the value it had
immediately before the command being undone started.

Global Non-Matched Command
Synopsis:
(1,$)v/RE/command list

This command shall be equivalent to the global command g except that the lines that are
marked during the first step shall be those for which the line excluding the terminating
<newline> does not match the RE.

Interactive Global Not-Matched Command
Synopsis:
(1,$)V/RE/

This command shall be equivalent to the interactive global command G except that the lines
that are marked during the first step shall be those for which the line excluding the
terminating <newline> does not match the RE.

Write Command
Synopsis:
(1,$)w [file]

The w command shall write the addressed lines into the file named by the pathname file.
The command shall create the file, if it does not exist, or shall replace the contents of
the existing file. The currently remembered pathname shall not be changed unless there is
no remembered pathname. If no pathname is given, the currently remembered pathname, if
any, shall be used (see the e and f commands); the current line number shall be unchanged.
If the command is successful, the number of bytes written shall be written to standard
output, unless the −s option was specified, in the following format:

"%d\n", <number of bytes written>

If file begins with '!', the rest of the line shall be taken to be a shell command line
whose standard input shall be the addressed lines. Such a shell command line shall not be
remembered as the current pathname. This usage of the write command with '!' shall not be
considered as a ``last w command that wrote the entire buffer'', as described previously;
thus, this alone shall not prevent the warning to the user if an attempt is made to
destroy the editor buffer via the e or q commands.

Line Number Command
Synopsis:
($)=

The line number of the addressed line shall be written to standard output in the following
format:

"%d\n", <line number>

The current line number shall be unchanged by this command.

Shell Escape Command
Synopsis:
!command

The remainder of the line after the '!' shall be sent to the command interpreter to be
interpreted as a shell command line. Within the text of that shell command line, the
unescaped character '%' shall be replaced with the remembered pathname; if a '!' appears
as the first character of the command, it shall be replaced with the text of the previous
shell command executed via '!'. Thus, "!!" shall repeat the previous !command. If any
replacements of '%' or '!' are performed, the modified line shall be written to the
standard output before command is executed. The ! command shall write:

"!\n"

to standard output upon completion, unless the −s option is specified. The current line
number shall be unchanged.

Null Command
Synopsis:
(.+1)

An address alone on a line shall cause the addressed line to be written. A <newline> alone
shall be equivalent to "+1p". The current line number shall be set to the address of the
written line.

EXIT STATUS


The following exit values shall be returned:

0 Successful completion without any file or command errors.

>0 An error occurred.

CONSEQUENCES OF ERRORS


When an error in the input script is encountered, or when an error is detected that is a
consequence of the data (not) present in the file or due to an external condition such as
a read or write error:

* If the standard input is a terminal device file, all input shall be flushed, and a new
command read.

* If the standard input is a regular file, ed shall terminate with a non-zero exit
status.

The following sections are informative.

APPLICATION USAGE


Because of the extremely terse nature of the default error messages, the prudent script
writer begins the ed input commands with an H command, so that if any errors do occur at
least some clue as to the cause is made available.

In earlier versions of this standard, an obsolescent option was described. This is no
longer specified. Applications should use the −s option. Using as a file operand now
produces unspecified results. This allows implementations to continue to support the
former required behavior.

EXAMPLES


None.

RATIONALE


The initial description of this utility was adapted from the SVID. It contains some
features not found in Version 7 or BSD-derived systems. Some of the differences between
the POSIX and BSD ed utilities include, but need not be limited to:

* The BSD option does not suppress the '!' prompt after a ! command.

* BSD does not support the special meanings of the '%' and '!' characters within a !
command.

* BSD does not support the addresses ';' and ','.

* BSD allows the command/suffix pairs pp, ll, and so on, which are unspecified in this
volume of POSIX.1‐2008.

* BSD does not support the '!' character part of the e, r, or w commands.

* A failed g command in BSD sets the line number to the last line searched if there are
no matches.

* BSD does not default the command list to the p command.

* BSD does not support the G, h, H, n, or V commands.

* On BSD, if there is no inserted text, the insert command changes the current line to
the referenced line −1; that is, the line before the specified line.

* On BSD, the join command with only a single address changes the current line to that
address.

* BSD does not support the P command; moreover, in BSD it is synonymous with the p
command.

* BSD does not support the undo of the commands j, m, r, s, or t.

* The Version 7 ed command W, and the BSD ed commands W, wq, and z are not present in
this volume of POSIX.1‐2008.

The −s option was added to allow the functionality of the removed option in a manner
compatible with the Utility Syntax Guidelines.

In early proposals there was a limit, {ED_FILE_MAX}, that described the historical
limitations of some ed utilities in their handling of large files; some of these have had
problems with files larger than 100000 bytes. It was this limitation that prompted much of
the desire to include a split command in this volume of POSIX.1‐2008. Since this limit was
removed, this volume of POSIX.1‐2008 requires that implementations document the file size
limits imposed by ed in the conformance document. The limit {ED_LINE_MAX} was also
removed; therefore, the global limit {LINE_MAX} is used for input and output lines.

The manner in which the l command writes non-printable characters was changed to avoid the
historical backspace-overstrike method. On video display terminals, the overstrike is
ambiguous because most terminals simply replace overstruck characters, making the l format
not useful for its intended purpose of unambiguously understanding the content of the
line. The historical <backslash>-escapes were also ambiguous. (The string "a\0011" could
represent a line containing those six characters or a line containing the three characters
'a', a byte with a binary value of 1, and a 1.) In the format required here, a <backslash>
appearing in the line is written as "\\" so that the output is truly unambiguous. The
method of marking the ends of lines was adopted from the ex editor and is required for any
line ending in <space> characters; the '$' is placed on all lines so that a real '$' at
the end of a line cannot be misinterpreted.

Earlier versions of this standard allowed for implementations with bytes other than eight
bits, but this has been modified in this version.

The description of how a NUL is written was removed. The NUL character cannot be in text
files, and this volume of POSIX.1‐2008 should not dictate behavior in the case of
undefined, erroneous input.

Unlike some of the other editing utilities, the filenames accepted by the E, e, R, and r
commands are not patterns.

Early proposals stated that the −p option worked only when standard input was associated
with a terminal device. This has been changed to conform to historical implementations,
thereby allowing applications to interpose themselves between a user and the ed utility.

The form of the substitute command that uses the n suffix was limited in some historical
documentation (where this was described incorrectly as ``backreferencing''). This limit
has been omitted because there is no reason why an editor processing lines of {LINE_MAX}
length should have this restriction. The command s/x/X/2047 should be able to substitute
the 2047th occurrence of 'x' on a line.

The use of printing commands with printing suffixes (such as pn, lp, and so on) was made
unspecified because BSD-based systems allow this, whereas System V does not.

Some BSD-based systems exit immediately upon receipt of end-of-file if all of the lines in
the file have been deleted. Since this volume of POSIX.1‐2008 refers to the q command in
this instance, such behavior is not allowed.

Some historical implementations returned exit status zero even if command errors had
occurred; this is not allowed by this volume of POSIX.1‐2008.

Some historical implementations contained a bug that allowed a single <period> to be
entered in input mode as <backslash> <period> <newline>. This is not allowed by ed
because there is no description of escaping any of the characters in input mode;
<backslash> characters are entered into the buffer exactly as typed. The typical method of
entering a single <period> has been to precede it with another character and then use the
substitute command to delete that character.

It is difficult under some modes of some versions of historical operating system terminal
drivers to distinguish between an end-of-file condition and terminal disconnect.
POSIX.1‐2008 does not require implementations to distinguish between the two situations,
which permits historical implementations of the ed utility on historical platforms to
conform. Implementations are encouraged to distinguish between the two, if possible, and
take appropriate action on terminal disconnect.

Historically, ed accepted a zero address for the a and r commands in order to insert text
at the start of the edit buffer. When the buffer was empty the command .= returned zero.
POSIX.1‐2008 requires conformance to historical practice.

For consistency with the a and r commands and better user functionality, the i and c
commands must also accept an address of 0, in which case 0i is treated as 1i and likewise
for the c command.

All of the following are valid addresses:

+++ Three lines after the current line.

/pattern/− One line before the next occurrence of pattern.

−2 Two lines before the current line.

3 −−−− 2 Line one (note the intermediate negative address).

1 2 3 Line six.

Any number of addresses can be provided to commands taking addresses; for example,
"1,2,3,4,5p" prints lines 4 and 5, because two is the greatest valid number of addresses
accepted by the print command. This, in combination with the <semicolon> delimiter,
permits users to create commands based on ordered patterns in the file. For example, the
command "3;/foo/;+2p" will display the first line after line 3 that contains the pattern
foo, plus the next two lines. Note that the address "3;" must still be evaluated before
being discarded, because the search origin for the "/foo/" command depends on this.

Historically, ed disallowed address chains, as discussed above, consisting solely of
<comma> or <semicolon> separators; for example, ",,," or ";;;" were considered an error.
For consistency of address specification, this restriction is removed. The following table
lists some of the address forms now possible:

┌────────┬───────┬───────┬────────────┬───────────────────────┐
AddressAddr1Addr2StatusComment
├────────┼───────┼───────┼────────────┼───────────────────────┤
│7, │ 7 │ 7 │ Historical │ │
│7,5, │ 5 │ 5 │ Historical │ │
│7,5,9 │ 5 │ 9 │ Historical │ │
│7,9 │ 7 │ 9 │ Historical │ │
│7,+ │ 7 │ 8 │ Historical │ │
│, │ 1 │ $ │ Historical │ │
│,7 │ 1 │ 7 │ Extension │ │
│,, │ $ │ $ │ Extension │ │
│,; │ $ │ $ │ Extension │ │
│7; │ 7 │ 7 │ Historical │ │
│7;5; │ 5 │ 5 │ Historical │ │
│7;5;9 │ 5 │ 9 │ Historical │ │
│7;5,9 │ 5 │ 9 │ Historical │ │
│7;$;4 │ $ │ 4 │ Historical │ Valid, but erroneous. │
│7;9 │ 7 │ 9 │ Historical │ │
│7;+ │ 7 │ 8 │ Historical │ │
│; │ . │ $ │ Historical │ │
│;7 │ . │ 7 │ Extension │ │
│;; │ $ │ $ │ Extension │ │
│;, │ $ │ $ │ Extension │ │
└────────┴───────┴───────┴────────────┴───────────────────────┘
Historically, ed accepted the '^' character as an address, in which case it was identical
to the <hyphen> character. POSIX.1‐2008 does not require or prohibit this behavior.

FUTURE DIRECTIONS


None.

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