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. The ed utility shall keep
track of whether the buffer has been modified. This shall be maintained as if via a tri-state internal flag with the state values
unchanged, changed, and changed-and-warned, which is:
-
Initially set to unchanged
-
Set to changed by any command that modifies the buffer
-
Set to unchanged by an e or E command that reloads (or empties) the buffer, or a w command that
writes the entire buffer
-
Set to either changed-and-warned or unchanged by an e or q command that warns an attempt was made to
destroy the editor buffer
A command that makes changes to the buffer in such a way that its contents are the same after the command (for example
s/a/a/) shall be considered to have modified the buffer, unless explicitly stated otherwise. In the remainder of the
description, this flag is referred to as the buffer change flag.
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 XBD 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.
The start and end of a regular expression (RE) are marked by a delimiter character (although in some circumstances the end
delimiter can be omitted). In addresses, the delimiter is either <slash> or <question-mark>. In commands, other
characters can be used as the delimiter, as specified in the description of the command. Within the RE (as an ed extension
to the BRE syntax), the delimiter shall not terminate the RE if it is the second character of an escape sequence (see XBD 9.1 Regular Expression Definitions) and the escaped delimiter shall be treated
as that literal character in the RE (losing any special meaning it would have had if it was not used as the delimiter and was not
escaped). In addition, the delimiter character shall not terminate the RE when it appears within a bracket expression, and shall
have its normal meaning in the bracket expression. For example, the command "g%[%]%p" is equivalent to "g/[%]/p",
and the command "s-[0-9]--g" is equivalent to "s/[0-9]//g".
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:
-
The <period> character ('.') shall address the current line.
-
The <dollar-sign> character ('$') shall address the last line of the edit buffer.
-
The positive decimal number n shall address the nth line of the edit buffer.
-
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.
-
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.
-
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.
-
A <plus-sign> ('+') or <hyphen-minus> character ('-') followed by a decimal number shall address
the current line plus or minus the number. A <plus-sign> or <hyphen-minus> 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-minus> 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-minus> 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 one or more addresses are provided to a command that requires zero addresses, it
shall be an error. Otherwise, if more than the maximum number of accepted addresses are provided to a command, the addresses shall
be evaluated from first to last and then discarded, until the maximum number of accepted addresses for that command remain.
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 shall
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:
|
Specified
|
Resulting
|
|
,
|
1 , $
|
|
, addr
|
1 , addr
|
|
addr ,
|
addr , addr
|
|
;
|
. ; $
|
|
; addr
|
. ; addr
|
|
addr ;
|
addr ; addr
|
If an address is omitted between two separators, the rule shall be applied to the first separator and the resulting
second address shall be used as the first address for the second separator. For example, with the address list ",," the
first ',' becomes "1,$" and the '$' is treated as the first address for the second ',',
resulting in "1,$,$".
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 the buffer change flag is currently set to changed, 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 buffer change flag set to either changed-and-warned or unchanged
and the current line number unchanged. If another e or q command is then attempted with no intervening command that
sets the buffer change flag to changed, it shall take effect.
If a terminal disconnect (see XBD 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.
In the following commands, if a closing delimiter would be the last character before a <newline> then that
character can be omitted with the behavior shown:
- For the g and v commands the addressed line(s) shall be written as if a closing delimiter followed
by a p were appended to the command.
- For the G and V commands no additional action shall be taken.
- For the s command, only the closing delimiter of the replacement can be omitted, in which case the result
of the substitution shall be written as if the p flag were appended.
- For the null command, the addressed line(s) shall be written as if the closing delimiter were appended.
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. If <text> is empty (that is,
the terminating '.' immediately follows the 'a'), the buffer change flag shall not be altered.
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.
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). If the pathname names a file that does not exist
and the buffer change flag is currently set to unchanged, it is unspecified whether this is treated as an error, or whether
the resulting buffer is emptied and a warning is written to standard error instead of writing the byte count to standard out. 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 change flag is currently set to
changed, 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 the current state of the buffer change flag.
Filename Command
- Synopsis:
-
f [file]
If file is given, the f command shall change the currently remembered pathname to file,
whether or not file names an existing 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,$)g/RE/command list
In the g command, the first step shall be to mark every line for which the line excluding the terminating
<newline> matches the given RE. Then, going sequentially from the beginning of the file to the end of the file, the given
command list shall be executed for each marked line, with the current line number set to the address of that line. Any line
modified by the command list shall be unmarked. When the g command completes, the current line number shall have the
value assigned by the last command in the command list. If there were no matching lines, the current line number shall not
be changed. A single command or the first of a list of commands shall appear on the same line as the global command. All lines of a
multi-line list except the last line shall be ended with a <backslash> preceding the terminating <newline>; the
a, i, and c commands and associated input are permitted. The '.' terminating input mode can be
omitted if it would be the last line of the command list. An empty command list shall be equivalent to the p
command. The use of the g, G, v, V, and ! commands in the command list produces undefined
results. Any character other than <backslash>, <space>, or <newline> can be used instead of a <slash> to
delimit the RE. Within the RE, in certain circumstances the RE delimiter can be used as a literal character; see Regular Expressions in ed.
Interactive Global Command
- Synopsis:
-
(1,$)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 <backslash>,
<space>, or <newline> can be used instead of a <slash> to delimit the RE. Within the RE, in certain circumstances
the RE delimiter can be used as a literal character; see Regular Expressions in ed.
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 is unspecified whether it causes the inserted text to be placed at
the beginning of the buffer or it is interpreted as if address 1 were specified. (These two allowed behaviors differ in the case
that the buffer is empty.) If <text> is empty (that is, the terminating '.' immediately follows the
'i'), the buffer change flag shall not be altered.
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 XBD 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 change flag is currently set to changed,
the user shall be warned, as described previously.
Quit Without Checking Command
- Synopsis:
-
Q
The Q command shall cause ed to exit without checking the current state of the buffer change
flag.
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.
If the number of bytes read is 0 it is unspecified whether the buffer change flag is set to changed or left
unaltered.
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.
Any character other than <backslash>, <space>, or <newline> can be used instead of a <slash> to delimit the
RE and the replacement. Within the RE, in certain circumstances the RE delimiter can be used as a literal character; see Regular Expressions in ed. Within the replacement, the delimiter shall not terminate the replacement if it
is the second character of an escape sequence (see XBD 9.1 Regular Expression
Definitions) and the escaped delimiter shall be treated as that literal character in the replacement (losing any special
meaning it would have had if it was not used as the delimiter and was not escaped). It shall be an error if the substitution fails
on every addressed line. The current line shall be set to the address of the last line on which a substitution occurred.
An unescaped <ampersand> ('&') appearing in the replacement shall be replaced by the string
matching the RE on the current line. As a more general feature, the characters '\n', where the <backslash> is
unescaped and 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 replacement, the replacement used in the most recent
substitute command shall be used as 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 escaped. 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 w command with '!' shall not alter the buffer change flag; 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.
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.1-2024.
- 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 j 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.1-2024.
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.1-2024. Since this limit was removed, this volume of POSIX.1-2024 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.1-2024 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.1-2024 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.1-2024.
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.1-2024 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.1-2024 requires conformance to
historical practice.
For consistency with the a and r commands and better user functionality, the i command also
accepts an address of 0. However, it is unspecified if 0i is treated as 1i (which will fail if the buffer is
empty), or means insert at the beginning of the buffer (which will succeed even if the buffer is empty). Earlier versions of this
standard required address 0 for the c command to be treated as 1 also, but this requirement has been removed, though
implementations are permitted to do this as an extension.
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.
More than the maximum number of accepted addresses can be provided to commands taking addresses; for example,
"1,2,3,4,5p" prints lines 4 and 5, because two is the maximum 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/" address 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:
|
Address
|
Addr1
|
Addr2
|
Status
|
Comment
|
|
7,
|
7
|
7
|
Historical
|
|
|
7,5,
|
5
|
5
|
Historical
|
|
|
7,5,9
|
5
|
9
|
Historical
|
|
|
7,9
|
7
|
9
|
Historical
|
|
|
7,+
|
7
|
.+
|
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-minus> character. POSIX.1-2024 does not require or prohibit this behavior.
Implementations are encouraged to set the buffer change flag to changed-and-warned when an e or
q command warns that an attempt was made to destroy the editor buffer. Some existing implementations set it to
unchanged, but this has the undesirable side-effect that a SIGHUP received after the warning is given does not write the
buffer to ed.hup.
![[Option Start]](../images/opt-start.gif)
Determine the location of messages objects and message catalogs. ![[Option End]](../images/opt-end.gif)