ch11_10.htm

unix基础教程

seconds since midnight, January 1, 1970, UTC.
The <em class="emphasis">format</em></tt> string is similar to that of
<tt class="literal">sprintf</tt>.
(See the Example for <b class="emphasis-bold"><a href="#systime">systime</a></b>.)
If <em class="emphasis">timestamp</em></tt> is omitted, it defaults to the
current time.
If <em class="emphasis">format</em></tt> is omitted, it defaults to a value
that produces output similar to that of <tt class="literal">date</tt>.
{G}</p>
</td></tr><tr><td valign="top"><a name="sub">sub</a></td><td><p><tt class="literal">sub(</tt><tt><em class="replaceable"><tt>r</em></tt><tt class="literal">,</tt> <tt><em class="replaceable">s</em></tt> [<tt class="literal">,</tt> <tt><em class="replaceable">t</tt></em></tt>]<tt class="literal">)</tt></p>
<p>
<a name="IXT-11-123344" />Substitute <em class="emphasis">s</em></tt> for first match of the
regular expression <em class="emphasis">r</em></tt> in the string <em class="emphasis">t</em></tt>.
If <em class="emphasis">t</em></tt> is not supplied,
defaults to <tt class="literal">$0</tt>.
Return 1 if successful; 0 otherwise.
{N}</p>
</td></tr><tr><td valign="top"><a name="substr">substr</a></td><td><p><tt class="literal">substr(</tt><tt><em class="replaceable"><tt>string</em></tt><tt class="literal">,</tt> <tt><em class="replaceable">beg</em></tt> <tt class="literal">[,</tt> <tt><em class="replaceable">len</tt></em></tt>]<tt class="literal">)</tt></p>
<p>
<a name="IXT-11-123345" />Return substring of <em class="emphasis">string</em></tt> at beginning
position <em class="emphasis">beg</em></tt> and the characters that
follow to maximum specified length <em class="emphasis">len</em></tt>.  If
no length is given, use the rest of the string.</p>
</td></tr><tr><td valign="top"><a name="system">system</a></td><td><p><tt class="literal">system(</tt><tt><em class="replaceable"><tt>command</tt></em></tt><tt class="literal">)</tt></p>
<p>
<a name="IXT-11-123346" />Function that executes the specified
<em class="emphasis">command</em></tt> and returns its status.  The status
of the executed command typically indicates success or failure.  A
value of 0 means that the command executed successfully. A nonzero
value indicates a failure of some sort.
The documentation for the command you're running will give you the
details.</p>
<p>The output of the command is <em class="emphasis">not</em></tt> available for processing
within the <tt class="literal">awk</tt> script.
Use <em class="emphasis">command</em></tt> <tt class="literal">| getline</tt>
to read the output of a command into the script.
{N}</p>
</td></tr><tr><td valign="top"><a name="systime">systime</a></td><td><p><tt class="literal">systime()</tt></p>
<p>
<a name="IXT-11-123347" />Return a
time-of-day value in
seconds since midnight, January 1, 1970, UTC.
{G}</p>
<h4 class="refsect2">Example</h4><p>Log the start and end times of a data-processing program:</p>

<blockquote><pre class="code">BEGIN {
	now = systime()
	mesg = strftime("Started at %m/%d/%Y %H:%M:%S", now)
	print mesg
}
<tt><em class="replaceable"><tt>process data ...</tt></em></tt>
END {
	now = systime()
	mesg = strftime("Ended at %m/%d/%Y %H:%M:%S", now)
	print mesg
}</pre></blockquote>

</td></tr><tr><td valign="top"><a name="tolower">tolower</a></td><td><p><tt class="literal">tolower(</tt><tt><em class="replaceable"><tt>str</tt></em></tt><tt class="literal">)</tt></p>
<p>
<a name="IXT-11-123348" />Translate all uppercase characters
in <em class="emphasis">str</em></tt> to lowercase and return the new string.<a href="#FOOTNOTE-15">[15]</a>
{N}</p><blockquote class="footnote"><a name="FOOTNOTE-15" /><p> [15]Very early versions of <tt class="literal">nawk</tt>
don't support <tt class="literal">tolower()</tt> and
<tt class="literal">toupper()</tt>. However, they are now part of
the POSIX specification for <tt class="literal">awk</tt>, and are
included in the SVR4 <tt class="literal">nawk</tt>.</p>
</blockquote>
</td></tr><tr><td valign="top"><a name="toupper">toupper</a></td><td><p><tt class="literal">toupper(</tt><tt><em class="replaceable"><tt>str</tt></em></tt><tt class="literal">)</tt></p>
<p>
<a name="IXT-11-123349" />Translate all lowercase characters
in <em class="emphasis">str</em></tt> to uppercase and return the new string.
{N}</p>
</td></tr><tr><td valign="top"><a name="while">while</a></td><td><p><tt class="literal">while (</tt><tt><em class="replaceable"><tt>condition</em></tt><tt class="literal">)</tt><br>&#160;&#160;&#160;&#160;<tt><em class="replaceable">statement</tt></em></tt></p>
<p>
<a name="IXT-11-123350" />Do <em class="emphasis">statement</em></tt> while <em class="emphasis">condition</em></tt> is true
(see <tt class="literal">if</tt> for a
description of allowable conditions).
A series of statements must be put within braces.</p>
</td></tr></table><p>

<a name="unut-ch-11-sect-10.1" /><div class="sect2"><h3 class="sect2">11.10.1. printf Formats</h3><p>Format specifiers for <tt class="literal">printf</tt> and <tt class="literal">sprintf</tt>
have the following form:</p>
<blockquote><pre class="code"><tt class="literal">%</tt>[<tt><em class="replaceable"><tt>flag</em></tt>][<tt><em class="replaceable">width</em></tt>][<tt class="literal">.</tt><tt><em class="replaceable">precision</tt></em></tt>]<tt class="literal">letter</tt></pre></blockquote><p>The control letter is required.
The format conversion control letters are as follows.</p>
<table border="1" cellpadding="3"><tr><th><em class="emphasis">Character</em></tt></th><th><em class="emphasis">Description</em></tt></th></tr>

<tr><td><tt class="literal">c</tt></td><td>ASCII character</td></tr>
<tr><td><tt class="literal">d</tt></td><td>Decimal integer</td></tr>
<tr><td><tt class="literal">i</tt></td><td>Decimal integer (added in POSIX)</td></tr>
<tr><td><tt class="literal">e</tt></td><td>Floating-point format ([-]<em class="emphasis">d</em></tt>.<em class="emphasis">precision</em></tt><tt class="literal">e</tt>[+-]<em class="emphasis">dd</em></tt>)</td></tr>
<tr><td><tt class="literal">E</tt></td><td>Floating-point format ([-]<em class="emphasis">d</em></tt>.<em class="emphasis">precision</em></tt><tt class="literal">E</tt>[+-]<em class="emphasis">dd</em></tt>)</td></tr>
<tr><td><tt class="literal">f</tt></td><td>Floating-point format ([-]<em class="emphasis">ddd</em></tt>.<em class="emphasis">precision</em></tt>)</td></tr>
<tr><td><tt class="literal">g</tt></td><td><tt class="literal">e</tt> or <tt class="literal">f</tt> conversion, whichever is shortest, with trailing zeros removed</td></tr>
<tr><td><tt class="literal">G</tt></td><td><tt class="literal">E</tt> or <tt class="literal">f</tt> conversion, whichever is shortest, with trailing zeros removed</td></tr>
<tr><td><tt class="literal">o</tt></td><td>Unsigned octal value</td></tr>
<tr><td><tt class="literal">s</tt></td><td>String</td></tr>
<tr><td><tt class="literal">x</tt></td><td>Unsigned hexadecimal number; uses <tt class="literal">a</tt>-<tt class="literal">f</tt> for 10 to 15</td></tr>
<tr><td><tt class="literal">X</tt></td><td>Unsigned hexadecimal number; uses <tt class="literal">A</tt>-<tt class="literal">F</tt> for 10 to 15</td></tr>
<tr><td><tt class="literal">%</tt></td><td>Literal <tt class="literal">%</tt></td></tr>
</table><p>
<p>The optional <em class="emphasis">flag</em></tt> is one of the following.</p>
<table border="1" cellpadding="3">

<tr><th><em class="emphasis">Character</em></tt></th><th><em class="emphasis">Description</em></tt></th></tr>

<tr><td><tt class="literal">-</tt></td><td><p>Left-justify the formatted value within the field.</p>
</td></tr>
<tr><td><em class="emphasis">space</em></tt></td><td><p>Prefix positive values with a space and negative values with a minus.</p>
</td></tr>
<tr><td><tt class="literal">+</tt></td><td><p>Always prefix numeric values with a sign,
even if the value is positive.</p>
</td></tr>
<tr><td><tt class="literal">#</tt></td><td><p>Use an alternate form:
<tt class="literal">%o</tt> has a preceding <tt class="literal">0</tt>;
<tt class="literal">%x</tt> and <tt class="literal">%X</tt> are prefixed with
<tt class="literal">0x</tt> and <tt class="literal">0X</tt>, respectively;
<tt class="literal">%e</tt>, <tt class="literal">%E</tt>, and <tt class="literal">%f</tt>
always have a decimal point in the result;
and
<tt class="literal">%g</tt> and <tt class="literal">%G</tt> do not have
trailing zeros removed.</p>
</td></tr>
<tr><td><tt class="literal">0</tt></td><td><p>Pad output with zeros, not spaces.
This happens only when the field width is wider than the converted result.</p>
</td></tr>
</table><p>
<p>The optional <em class="emphasis">width</em></tt> is the minimum number of characters to
output.
The result will be padded to this size if it is smaller.
The <tt class="literal">0</tt> flag causes padding with zeros; otherwise,
padding is with spaces.</p>
<p>The <em class="emphasis">precision</em></tt> is optional.
Its meaning varies by control letter,
as shown in this table.</p>
<table border="1" cellpadding="3"><tr><th><em class="emphasis">Conversion</em></tt></th><th><em class="emphasis">Precision Means</em></tt></th></tr>


<tr><td><p><tt class="literal">%d</tt>, <tt class="literal">%i</tt>, <tt class="literal">%o</tt></p>
<p><tt class="literal">%u</tt>, <tt class="literal">%x</tt>, <tt class="literal">%X</tt></p>
</td>

<td>The minimum number of digits to print</td></tr>


<tr><td><tt class="literal">%e</tt>, <tt class="literal">%E</tt>, <tt class="literal">%f</tt></td>

<td>The number of digits to the right of the decimal point</td></tr>


<tr><td><tt class="literal">%g</tt>, <tt class="literal">%G</tt></td><td>The maximum number of significant digits</td></tr>
<tr><td><tt class="literal">%s</tt></td><td>The maximum number of characters to print</td></tr>
</table><p>
<a name="IXT-11-123351" />
<a name="IXT-11-123352" />
<a name="IXT-11-123353" /></div>



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