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unix 下的C开发手册,还用详细的例程。

command can be appended to any command other than
<b>e</b>,
<b>E</b>,
<b>f</b>,
<b>q</b>,
<b>Q</b>,
<b>r</b>,
<b>w</b>
or
<b>!</b>.
<h5><a name = "tag_001_014_541_021">&nbsp;</a>Prompt Command</h5>
<pre>
<code>
<i>Synopsis</i>:	P
</code>
</pre>
<p>
The
<b>P</b>
command causes
<i>ed</i>
to prompt with an asterisk
(*)
(or
<i>string</i>,
if
<b>-p</b>
is specified)
for all subsequent commands.
The
<b>P</b>
command alternatively turns this mode on and off; it is
initially on if the
<b>-p</b>
option is specified, otherwise off.
The current line number is unchanged.
<h5><a name = "tag_001_014_541_022">&nbsp;</a>Quit Command</h5>
<pre>
<code>
<i>Synopsis</i>:	q
</code>
</pre>
<p>
The
<b>q</b>
command causes
<i>ed</i>
to exit.
If the buffer has changed since the last time the entire buffer
was written, the user will be warned, as described previously.
<h5><a name = "tag_001_014_541_023">&nbsp;</a>Quit Without Checking Command</h5>
<pre>
<code>
<i>Synopsis</i>:	Q
</code>
</pre>
<p>
The
<b>Q</b>
command causes
<i>ed</i>
to exit without
checking if changes have been made in the buffer since the last
<b>w</b>
command.
<h5><a name = "tag_001_014_541_024">&nbsp;</a>Read Command</h5>
<pre>
<code>
<i>Synopsis</i>:	($)r<b>[</b><i>file</i><b>]</b>
</code>
</pre>
<p>
<br>
The
<b>r</b>
command reads in the file named by the pathname
<i>file</i>
and appends it after the addressed line.
If no
<i>file</i>
argument is given, the currently remembered pathname,
if any, will be used
(see
<b>e</b>
and
<b>f</b>
commands).
The currently remembered pathname will not be changed unless
there is no remembered pathname.
Address 0 is valid for
<b>r</b>
and causes the file to be read at the beginning of the buffer.
If the read is successful, and
<b>-s</b>
was not specified, the number of bytes
read will be written to standard output
in the following format:
<p><code>
<tt>"%d\n"</tt>, &lt;<i>number&nbsp;of&nbsp;bytes&nbsp;read</i>&gt;
</code>
The current line number will be set to the address of the last line read in.
If
<i>file</i>
is replaced by
<b>!</b>,
the rest of the line
will be taken to be a
shell command line whose output is to be read.
Such a shell command line will not be remembered as the current pathname.
<h5><a name = "tag_001_014_541_025">&nbsp;</a>Substitute Command</h5>
<pre>
<code>
<i>Synopsis</i>:	(.,.)s/<i>RE</i>/<i>replacement</i>/<i>flags</i>
</code>
</pre>
<p>
The
<b>s</b>
command searches each addressed
line for an occurrence of the specified RE
and replace either the first or
all (non-overlapped) matched strings with the
<i>replacement</i>;
see the following description of the
<b>g</b>
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
<i>RE</i>
and the replacement.
Within the
<i>RE</i>,
the
<i>RE</i>
delimiter itself can be used as a literal
character if it is preceded by a backslash.
The current line will be set to the address of the last line
on which a substitution occurred.
<p>
An ampersand
(&amp;)
appearing in the
<i>replacement</i>
will be replaced by the string matching the RE on the current line.
The special meaning of "&amp;"
in this context can be
suppressed by preceding it by backslash.
As a more general feature,
the characters
<b>\</b><i>n</i>,
where
<i>n</i>
is a digit,
will be replaced by the text matched by the
corresponding back-reference expression.
When the character
"%"
is the only character
in the
<i>replacement</i>,
the
<i>replacement</i>
used in the most recent substitute
command will be used as the
<i>replacement</i>
in the current substitute command;
if there was no previous substitute command,
the use of
"%"
in this manner is an error.
The
"%"
loses 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
<i>replacement</i>
from beginning to end, the following character loses its special meaning
(if any).
It is unspecified what special meaning is given to any character
other than "&amp;", "\" "%" or digits.
<p>
A line can be split by substituting a newline character into it.
The application must escape the newline character in the
<i>replacement</i>
by preceding it by backslash.
Such substitution cannot be done as part of a
<b>g</b> or <b>v</b> command list.
The current line number will be set to the address of the last line
on which a substitution is performed.
If no substitution is
performed, the current line number is unchanged.
If a line is
split, a substitution is considered to have been performed on
each of the new lines for the purpose of determining the new
current line number.
A substitution is considered to have been
performed even if the replacement string is identical to the
string that it replaces.
<p>
The value of
<i>flags</i>
must be zero or more of:
<dl compact>

<dt><i>count</i><dd>Substitute for the
<i>count</i>th
occurrence only of the
<i>RE</i>
found on each addressed line.

<dt><b>g</b><dd>Globally substitute for all non-overlapping instances of the
<i>RE</i>
rather than just the first one.
If both
<b>g</b>
and
<i>count</i>
are specified,
the results are unspecified.

<dt><b>l</b><dd>Write to standard output
the final line in which a substitution was made.
The line will be written
in the format specified for the
<b>l</b>
command.

<dt><b>n</b><dd>Write to standard output
the final line in which a substitution was made.
The line will be written
in the format specified for the
<b>n</b>
command.

<dt><b>p</b><dd>Write to standard output
the final line in which a substitution was made.
The line will be written
in the format specified for the
<b>p</b>
command.

</dl>
<h5><a name = "tag_001_014_541_026">&nbsp;</a>Copy Command</h5>
<pre>
<code>
<i>Synopsis</i>:	(.,.)t<i>address</i>
</code>
</pre>
<p>
The
<b>t</b>
command is equivalent to the
<b>m</b>
command, except that a copy of the addressed lines will be placed
after address
<i>address</i>
(which can be 0);
the current line number will be set to the address of the last line added.
<h5><a name = "tag_001_014_541_027">&nbsp;</a>Undo Command</h5>
<pre>
<code>
<i>Synopsis</i>:	u
</code>
</pre>
<p>
The
<b>u</b>
command nullifies the effect of the most recent
command that modified anything in the buffer, namely
the most recent
<b>a</b>,
<b>c</b>,
<b>d</b>,
<b>g</b>,
<b>i</b>,
<b>j</b>,
<b>m</b>,
<b>r</b>,
<b>s</b>,
<b>t</b>,
<b>u</b>,
<b>v</b>,
<b>G</b>
or
<b>V</b>
command.
All changes made to the buffer by a
<b>g</b>,
<b>G</b>,
<b>v</b>
or
<b>V</b>
global command will be undone as a single change;
if no changes were made by the global command (such as with
<b>g/</b>RE
the
<b>u</b>
command will have no effect.
The current line number will be set to the value it had
immediately before the
command being undone started.
<h5><a name = "tag_001_014_541_028">&nbsp;</a>Global Non-matched Command</h5>
<pre>
<code>
<i>Synopsis</i>:	(1,$)v/<i>RE</i>/<i>command list</i>
</code>
</pre>
<p>
This command is equivalent to the global command
<b>g</b>
except that the
lines that are marked during the first step will be those that do
not match the
<i>RE</i>.
<h5><a name = "tag_001_014_541_029">&nbsp;</a>Interactive Global Not-matched Command</h5>
<pre>
<code>
<i>Synopsis</i>:	(1,$)V/<i>RE</i>/
</code>
</pre>
<p>
This command is equivalent to the interactive global command
<b>G</b> except
that the lines that are marked during the first step will be those that do
not match the
<i>RE</i>.
<h5><a name = "tag_001_014_541_030">&nbsp;</a>Write Command</h5>
<pre>
<code>
<i>Synopsis</i>:	(1,$)w<b>[</b><i>file</i><b>]
</b></code>
</pre>
<p>
The
<b>w</b>
command writes the addressed lines into
the file named by the pathname
<i>file</i>.
The command will create the file, if it does not exist, or
will replace the contents of the existing file.
The currently remembered pathname will not be changed unless
there is no remembered pathname.
If no pathname is given, the currently remembered pathname, if any,
will be used (see the
<b>e</b>
and
<b>f</b>
commands); the current line number is unchanged.
If the command is successful, the number of bytes written will be
written to standard output, unless the
<b>-s</b>
option was specified, in the following format:
<p><code>
<tt>"%d\n"</tt>, &lt;<i>number&nbsp;of&nbsp;bytes&nbsp;written</i>&gt;
</code>
<p>
If
<i>file</i>
begins with "!", the rest of the line will be taken to be a
shell command line whose standard input will be the addressed lines.
Such a shell command line will not be remembered as the current pathname.
This usage of the write command with "!" will not be considered as a &quot;last
<b>w</b>
command that wrote the entire buffer&quot;, as described previously;
thus, this alone will not prevent
the warning to the user if an attempt is made to destroy
the editor buffer via the
<b>e</b>
or
<b>q</b>
commands.
<h5><a name = "tag_001_014_541_031">&nbsp;</a>Line Number Command</h5>
<pre>
<code>
<i>Synopsis</i>:	($)=
</code>
</pre>
<p>
The line number of the addressed line will be
written to standard output
in the following format:
<p><code>
<tt>"%d\n"</tt>, &lt;<i>line&nbsp;number</i>&gt;
</code>
<p>
The current line number is unchanged by this command.
<h5><a name = "tag_001_014_541_032">&nbsp;</a>Shell Escape Command</h5>
<pre>
<code>
<i>Synopsis</i>:	!<i>command</i>
</code>
</pre>
<p>
The remainder of the line after the
<b>!</b>
will 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
<b>%</b>
will be replaced with the remembered pathname;
if a
<b>!</b>
appears as the first character of the command,
it will be replaced with the text of the previous shell command
executed via
<b>!</b>.
Thus,
<b>!!</b>
will repeat the previous
<b>!</b>command
If any replacements of
<b>%</b>
or
<b>!</b>
are performed, the modified line will be written
to the standard output before
<i>command</i>
is executed.
The
<b>!</b>
command will write:
<pre>
<code>
"!\n"
</code>
</pre>
to standard output upon completion, unless the
<b>-s</b>
option is specified.
The current line number is unchanged.
<h5><a name = "tag_001_014_541_033">&nbsp;</a>Null Command</h5>
<pre>
<code>
<i>Synopsis</i>:	(.+1)
</code>
</pre>
<p>
An address alone on a line causes the addressed line to be written.
A newline character alone is equivalent to
.+1p.
The current line number will be set to the address of the written line.
</blockquote><h4><a name = "tag_001_014_542">&nbsp;</a>EXIT STATUS</h4><blockquote>
The following exit values are returned:
<dl compact>

<dt>0<dd>Successful completion without any file or command errors.

<dt>&gt;0<dd>An error occurred.

</dl>
</blockquote><h4><a name = "tag_001_014_543">&nbsp;</a>CONSEQUENCES OF ERRORS</h4><blockquote>
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:
<ul>
<p>
<li>
If the standard input is a terminal device file,
all input will be flushed, and a new command read.
<p>
<li>
If the standard input is a regular file,
<i>ed</i>
will terminate with a non-zero exit status.
<p>
</ul>
</blockquote><h4><a name = "tag_001_014_544">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
Because of the extremely terse nature of the default error
messages, the prudent script writer
will begin the
<i>ed</i>
input commands with an
<b>H</b>
command, so that if any errors do occur at
least some clue as to the cause will be made available.
</blockquote><h4><a name = "tag_001_014_545">&nbsp;</a>EXAMPLES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_546">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
The obsolescent single-minus form may be withdrawn in a future issue.
Applications should use the
<b>-s</b>
option.
<p>
The IEEE PASC 1003.2 Interpretations Committee has forwarded concerns about 
parts of this interface definition to the IEEE PASC Shell and Utilities Working Group
which is identifying the corrections.
A future revision of this specification will align with
IEEE Std. 1003.2b when finalised.
</blockquote><h4><a name = "tag_001_014_547">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="ex.html">ex</a></i>,
<i><a href="sed.html">sed</a></i>,
<i><a href="sh.html">sh</a></i>,
<i><a href="vi.html">vi</a></i>.
</blockquote><hr size=2 noshade>
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