ch10_05.htm

unix基础教程

lines.)  Using <tt class="literal">\n</tt> to match the embedded newline, you can match
patterns across multiple lines.  See Example under <b class="emphasis-bold"><a href="#D">D</a></b>.</p>
<h4 class="refsect2">Examples</h4><p>Like the Example in <b class="emphasis-bold">n</b>, but print <tt class="literal">.NH</tt> line as well as header title:</p>
<blockquote><pre class="code">/^\.NH/{
N
p
}</pre></blockquote>
<p>Join two lines (replace newline with space):</p>
<blockquote><pre class="code">/^\.NH/{
N
s/\n/ /
p
}</pre></blockquote>

</td></tr><tr><td valign="top">p</td><td><p>[<em class="replaceable"><tt>address1</em>[<tt class="literal">,</tt><em class="replaceable">address2</tt></em>]]<tt class="literal">p</tt></p>
<p>
<a name="IXT-10-123251" />Print the addressed line(s).  Note that this can result in duplicate
output unless default output is suppressed using <tt class="literal">#n</tt> or
the <tt class="literal">-n</tt>
command-line option.  Typically used before commands that change flow
control (<tt class="literal">d</tt>, <tt class="literal">n</tt>,
<tt class="literal">b</tt>) and might prevent the current line from being
output.
See Examples under <b class="emphasis-bold"><a href="#h">h</a></b>,
<b class="emphasis-bold"><a href="#n">n</a></b>, and <b class="emphasis-bold"><a href="#N">N</a></b>.</p>
</td></tr><tr><td valign="top">P</td><td><p>[<em class="replaceable"><tt>address1</em>[<tt class="literal">,</tt><em class="replaceable">address2</tt></em>]]<tt class="literal">P</tt></p>
<p>
<a name="IXT-10-123252" />Print first part (up to embedded newline) of multiline pattern space created
by <tt class="literal">N</tt> command.  Same as <tt class="literal">p</tt> if <tt class="literal">N</tt> has not been applied
to a line.</p>
<h4 class="refsect2">Example</h4><p>Suppose you have function references in two formats:</p>
<blockquote><pre class="code">function(arg1, arg2)
function(arg1,
         arg2)</pre></blockquote>
<p>The following script changes argument <tt class="literal">arg2</tt>, regardless of whether 
it appears on the same line as the function name:</p>
<blockquote><pre class="code">s/function(arg1, arg2)/function(arg1, XX)/
/function(/{
N
s/arg2/XX/
P
D
}</pre></blockquote>

</td></tr><tr><td valign="top">q</td><td><p>[<em class="replaceable"><tt>address</tt></em>]<tt class="literal">q</tt></p>
<p>
<a name="IXT-10-123253" />Quit when <em class="emphasis">address</em> is encountered.
The addressed line is first
written to the output (if default output is not suppressed),
along with any text appended to it by 
previous <tt class="literal">a</tt> or <tt class="literal">r</tt> commands.</p>
<h4 class="refsect2">Examples</h4><p>Delete everything after the addressed line:</p>
<blockquote><pre class="code">/Garbled text follows:/q</pre></blockquote>
<p>Print only the first 50 lines of a file:</p>
<blockquote><pre class="code">50q</pre></blockquote>

</td></tr><tr><td valign="top">r</td><td><p>[<em class="replaceable"><tt>address</em>]<tt class="literal">r</tt> <em class="replaceable">file</tt></em></p>
<p>
<a name="IXT-10-123254" />Read contents of <em class="emphasis">file</em> and append after the contents of the
pattern space.
There must be
exactly one space between the <tt class="literal">r</tt> and the filename.</p>
<h4 class="refsect2">Example</h4><blockquote><pre class="code">/The list of items follows:/r item_file</pre></blockquote>

</td></tr><tr><td valign="top">s</td><td><p>[<em class="replaceable"><tt>address1</em>[<tt class="literal">,</tt><em class="replaceable">address2</em>]]<tt class="literal">s/</tt><em class="replaceable">pattern</em><tt class="literal">/</tt><em class="replaceable">replacement</em><tt class="literal">/</tt>[<em class="replaceable">flags</tt></em>]</p>
<p>
<a name="IXT-10-123255" />Substitute <em class="emphasis">replacement</em> for <em class="emphasis">pattern</em> on each addressed line.
If pattern addresses are used, the pattern <tt class="literal">//</tt> represents the last
pattern address specified.
Any delimiter may be used. Use <tt class="literal">\</tt> within
<em class="emphasis">pattern</em> or <em class="emphasis">replacement</em>
to escape the delimiter.
The following flags can be specified:</p>
<dl><dt><tt class="literal">g</tt></dt><dd>Replace all instances of <em class="emphasis">pattern</em></tt> on each addressed line, not
just the first instance.</p>
</dd>
<dt><tt class="literal">p</tt></dt><dd>Print the line if a successful substitution is done.  If several
successful substitutions are done,
<tt class="literal">sed</tt> prints multiple copies of the line.</p>
</dd>
<dt><tt class="literal">w</tt> <tt><em class="replaceable">file</em></tt></dt><dd>Write the line to <em class="emphasis">file</em></tt> if a replacement was done.  A maximum
of 10 different <em class="emphasis">files</em></tt> can be opened.</p>
</dd>
<dt><i><em class="emphasis">n</em></tt></i></dt><dd>Replace <em class="emphasis">n</em></tt>th instance of
<em class="emphasis">pattern</em> on each addressed line.
<em class="emphasis">n</em> is any number in the range 1 to 512, and the default is 1.</p>
</dd>
</dl>
<h4 class="refsect2">Examples</h4><p>Here are some short, commented scripts:</p>
<blockquote><pre class="code"># Change third and fourth quote to ( and ):
/function/{
s/"/(/3
s/"/)/4
}

# Remove all quotes on a given line:
/Title/s/"//g

# Remove first colon and all quotes; print resulting lines:
s/://p
s/"//gp

# Change first "if" but leave "ifdef" alone:
/ifdef/!s/if/   if/</pre></blockquote>

</td></tr><tr><td valign="top">t</td><td><p>[<em class="replaceable"><tt>address1</em>[<tt class="literal">,</tt><em class="replaceable">address2</em>]]<tt class="literal">t</tt> [<em class="replaceable">label</tt></em>]</p>
<p>
<a name="IXT-10-123256" />Test if successful substitutions have been made on addressed lines,
and if so, branch to the line marked by <tt class="literal">:</tt><em class="emphasis">label</em>
(see <b class="emphasis-bold"><a href="#b">b</a></b> and <b class="emphasis-bold"><a href="#:">:</a></b>).  If
<em class="emphasis">label</em> is not specified, control branches to the bottom of
the script.
The <tt class="literal">t</tt> command is like a case statement in the C
programming language or the various shell programming languages.
You test each case:  when it's true, you exit the construct.</p>
<h4 class="refsect2">Example</h4><p>Suppose you want to fill empty fields of a database.  You have this:</p>
<blockquote><pre class="code">ID: 1   Name: greg   Rate: 45
ID: 2   Name: dale
ID: 3</pre></blockquote>
<p>You want this:</p>
<blockquote><pre class="code">ID: 1   Name: greg   Rate: 45   Phone: ??
ID: 2   Name: dale   Rate: ??   Phone: ??
ID: 3   Name: ????   Rate: ??   Phone: ??</pre></blockquote>
<p>You need to test the number of fields already there.
Here's the script (fields are tab-separated):</p>





<blockquote><pre class="code">#n
/ID/{
s/ID: .* Name: .* Rate: .*/&amp;   Phone: ??/p
t
s/ID: .* Name: .*/&amp;   Rate: ??   Phone: ??/p
t
s/ID: .*/&amp;   Name: ????   Rate: ??   Phone: ??/p
}</pre></blockquote>

</td></tr><tr><td valign="top">w</td><td><p>[<em class="replaceable"><tt>address1</em>[<tt class="literal">,</tt><em class="replaceable">address2</em>]]<tt class="literal">w</tt><em class="replaceable"> file</tt></em></p>
<p>
<a name="IXT-10-123257" />Append contents of pattern space to <em class="emphasis">file</em>.  This action occurs
when the command is encountered rather than when the pattern space is
output.  Exactly one space
must separate the <tt class="literal">w</tt> and the filename.
A maximum of 10 different files can be opened in a script.
This command creates the file if it does not exist; if the file
exists, its contents are overwritten each time the script
is executed.  Multiple write commands that direct output to the
same file append to the end of the file.</p>
<h4 class="refsect2">Example</h4><blockquote><pre class="code"># Store tbl and eqn blocks in a file:
/^\.TS/,/^\.TE/w troff_stuff
/^\.EQ/,/^\.EN/w troff_stuff</pre></blockquote>

</td></tr><tr><td valign="top">x</td><td><p>[<em class="replaceable"><tt>address1</em>[<tt class="literal">,</tt><em class="replaceable">address2</tt></em>]]<tt class="literal">x</tt></p>
<p>
<a name="IXT-10-123258" />Exchange the contents of the pattern space with the contents of the
hold space.  See <b class="emphasis-bold"><a href="#h">h</a></b> for an example.</p>
</td></tr><tr><td valign="top">y</td><td><p>[<em class="replaceable"><tt>address1</em>[<tt class="literal">,</tt><em class="replaceable">address2</em>]]<tt class="literal">y/</tt><em class="replaceable">abc</em><tt class="literal">/</tt><em class="replaceable">xyz</tt></em><tt class="literal">/</tt></p>
<p>
<a name="IXT-10-123259" />Translate characters.  Change every instance of <em class="emphasis">a</em>
to <em class="emphasis">x</em>, <em class="emphasis">b</em> to <em class="emphasis">y</em>, <em class="emphasis">c</em> to <em class="emphasis">z</em>, etc.</p>
<h4 class="refsect2">Example</h4><blockquote><pre class="code"># Change item 1, 2, 3 to Item A, B, C ...
/^item [1-9]/y/i123456789/IABCDEFGHI/</pre></blockquote>

</td></tr></table><p>

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