Originální popis anglicky:
ed - edit text
Návod, kniha: POSIX Programmer's Manual
ed [-p
string][-s][file]
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.
The
ed utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
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.
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. If the
file operand is '-' , the results are unspecified.
The standard input shall be a text file consisting of commands, as described in
the EXTENDED DESCRIPTION section.
The input files shall be text files.
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
IEEE Std 1003.1-2001, 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 .
The
ed utility shall take the standard action for all signals (see the
ASYNCHRONOUS EVENTS section in
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 returning to command
mode.
- SIGQUIT
- The ed utility shall ignore this event.
Various editing commands and the prompting feature (see
-p) write to
standard output, as described in the EXTENDED DESCRIPTION section.
The standard error shall be used only for diagnostic messages.
The output files shall be text files whose formats are dependent on the editing
commands given.
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.
The
ed utility shall support basic regular expressions, as described in
the Base Definitions volume of IEEE Std 1003.1-2001, Section
9.3, Basic Regular Expressions. Since regular expressions in
ed are
always matched against single lines (excluding the terminating
<newline>s), 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.
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:
| Specified |
Resulting |
| , |
1 , $ |
| , addr |
1 , addr |
| addr , |
addr , addr |
| ; |
. ; $ |
| ; addr |
. ; addr |
| addr ; |
addr ; addr |
Any <blank>s included between addresses, address separators, or address
offsets shall be ignored.
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>s. The
command letter can be preceded by zero or more <blank>s. 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>s.
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:
(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 is detected:
- *
- 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
to a file named ed.hup in the current directory. If this write
fails, ed shall attempt to write a copy of the buffer to a filename
ed.hup in the directory named by the HOME environment
variable. If both these attempts fail, ed shall exit without saving
the buffer.
- *
- The ed utility shall not write the file to the
currently remembered pathname or return to command mode, and shall
terminate with a non-zero exit status.
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:
(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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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:
The current line number shall be unchanged.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
The
j command shall join contiguous lines by removing the appropriate
<newline>s. 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.
- Synopsis:
-
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.
- Synopsis:
-
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 IEEE Std 1003.1-2001, 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). If the size of a byte on the
system is greater than nine bits, the format used for non-printable characters
is implementation-defined.
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.
- Synopsis:
-
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.
- Synopsis:
-
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
!.
- Synopsis:
-
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
!.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
The
Q command shall cause
ed to exit without checking whether
changes have been made in the buffer since the last
w command.
- Synopsis:
-
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.
- 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. 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
'&' ,
'\' ,
'%' , 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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
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.
- Synopsis:
-
The line number of the addressed line shall be written to standard output in the
following format:
The current line number shall be unchanged by this command.
- Synopsis:
-
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:
to standard output upon completion, unless the
-s option is specified.
The current line number shall be unchanged.
- Synopsis:
-
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 following exit values shall be returned:
- 0
- Successful completion without any file or command
errors.
- >0
- An error occurred.
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.
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 previous versions, 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.
None.
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
IEEE Std 1003.1-2001.
- *
- 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 IEEE Std 1003.1-2001.
The
-s option was added to allow the functionality of the now withdrawn
- 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 IEEE Std 1003.1-2001. Since this limit
was removed, this volume of IEEE Std 1003.1-2001 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>s; the
'$' is placed on
all lines so that a real
'$' at the end of a line cannot be
misinterpreted.
Systems with bytes too large to fit into three octal digits must devise other
means of displaying non-printable characters. Consideration was given to
requiring that the number of octal digits be large enough to hold a byte, but
this seemed to be too confusing for applications on the vast majority of
systems where three digits are adequate. It would be theoretically possible
for the application to use the
getconf utility to find out the CHAR_BIT
value and deal with such an algorithm; however, there is really no portable
way that an application can use the octal values of the bytes across various
coded character sets, so the additional specification was not worthwhile.
The description of how a NUL is written was removed. The NUL character cannot be
in text files, and this volume of IEEE Std 1003.1-2001 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
IEEE Std 1003.1-2001 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
IEEE Std 1003.1-2001.
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; backslashes 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. IEEE Std 1003.1-2001 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 betw
