awk.html

IEEE 1003.1-2003, Single Unix Specification v3

<td align="left">
<p class="tent">Left</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">( <i>index</i> ) in <i>array</i></p>
</td>
<td align="left">
<p class="tent">Multi-dimension array</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Left</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">&nbsp;</p>
</td>
<td align="left">
<p class="tent">membership</p>
</td>
<td align="left">
<p class="tent">&nbsp;</p>
</td>
<td align="left">
<p class="tent">&nbsp;</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent"><i>expr</i> &amp;&amp; <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Logical AND</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Left</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent"><i>expr</i> || <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Logical OR</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Left</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent"><i>expr1</i> ? <i>expr2</i> : <i>expr3</i></p>
</td>
<td align="left">
<p class="tent">Conditional expression</p>
</td>
<td align="left">
<p class="tent">Type of selected</p>
</td>
<td align="left">
<p class="tent">Right</p>
</td>
</tr>

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<td align="left">
<p class="tent">&nbsp;</p>
</td>
<td align="left">
<p class="tent">&nbsp;</p>
</td>
<td align="left">
<p class="tent"><i>expr2</i> or <i>expr3</i></p>
</td>
<td align="left">
<p class="tent">&nbsp;</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">lvalue ^= <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Exponentiation assignment</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Right</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">lvalue %= <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Modulus assignment</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Right</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">lvalue *= <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Multiplication assignment</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Right</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">lvalue /= <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Division assignment</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Right</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">lvalue += <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Addition assignment</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Right</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">lvalue -= <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Subtraction assignment</p>
</td>
<td align="left">
<p class="tent">Numeric</p>
</td>
<td align="left">
<p class="tent">Right</p>
</td>
</tr>

<tr valign="top">
<td align="left">
<p class="tent">lvalue = <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Assignment</p>
</td>
<td align="left">
<p class="tent">Type of <i>expr</i></p>
</td>
<td align="left">
<p class="tent">Right</p>
</td>
</tr>
</table>
</center>

<p>Each expression shall have either a string value, a numeric value, or both. Except as stated for specific contexts, the value of
an expression shall be implicitly converted to the type needed for the context in which it is used. A string value shall be
converted to a numeric value by the equivalent of the following calls to functions defined by the ISO&nbsp;C standard:</p>

<pre>
<tt>setlocale(LC_NUMERIC, "");
</tt><i>numeric_value</i> <tt>= atof(</tt><i>string_value</i><tt>);
</tt>
</pre>

<p>A numeric value that is exactly equal to the value of an integer (see <a href="xcu_chap01.html#tag_01_07_02"><i>Concepts Derived
from the ISO C Standard</i></a> ) shall be converted to a string by the equivalent of a call to the <b>sprintf</b> function (see <a
href="#tag_04_06_13_13">String Functions</a> ) with the string <tt>"%d"</tt> as the <i>fmt</i> argument and the numeric value being
converted as the first and only <i>expr</i> argument. Any other numeric value shall be converted to a string by the equivalent of a
call to the <b>sprintf</b> function with the value of the variable <b>CONVFMT</b> as the <i>fmt</i> argument and the numeric value
being converted as the first and only <i>expr</i> argument. The result of the conversion is unspecified if the value of
<b>CONVFMT</b> is not a floating-point format specification. This volume of IEEE&nbsp;Std&nbsp;1003.1-2001 specifies no explicit
conversions between numbers and strings. An application can force an expression to be treated as a number by adding zero to it, or
can force it to be treated as a string by concatenating the null string ( <tt>""</tt> ) to it.</p>

<p>A string value shall be considered a <i>numeric string</i> if it comes from one of the following:</p>

<ol>
<li>
<p>Field variables</p>
</li>

<li>
<p>Input from the <i>getline</i>() function</p>
</li>

<li>
<p><b>FILENAME</b></p>
</li>

<li>
<p><b>ARGV</b> array elements</p>
</li>

<li>
<p><b>ENVIRON</b> array elements</p>
</li>

<li>
<p>Array elements created by the <i>split</i>() function</p>
</li>

<li>
<p>A command line variable assignment</p>
</li>

<li>
<p>Variable assignment from another numeric string variable</p>
</li>
</ol>

<p>and after all the following conversions have been applied, the resulting string would lexically be recognized as a <b>NUMBER</b>
token as described by the lexical conventions in <a href="#tag_04_06_13_16">Grammar</a> :</p>

<ul>
<li>
<p>All leading and trailing &lt;blank&gt;s are discarded.</p>
</li>

<li>
<p>If the first non- &lt;blank&gt; is <tt>'+'</tt> or <tt>'-'</tt> , it is discarded.</p>
</li>

<li>
<p>Changing each occurrence of the decimal point character from the current locale to a period.</p>
</li>
</ul>

<p>If a <tt>'-'</tt> character is ignored in the preceding description, the numeric value of the <i>numeric string</i> shall be the
negation of the numeric value of the recognized <b>NUMBER</b> token. Otherwise, the numeric value of the <i>numeric string</i>
shall be the numeric value of the recognized <b>NUMBER</b> token. Whether or not a string is a <i>numeric string</i> shall be
relevant only in contexts where that term is used in this section.</p>

<p>When an expression is used in a Boolean context, if it has a numeric value, a value of zero shall be treated as false and any
other value shall be treated as true. Otherwise, a string value of the null string shall be treated as false and any other value
shall be treated as true. A Boolean context shall be one of the following:</p>

<ul>
<li>
<p>The first subexpression of a conditional expression</p>
</li>

<li>
<p>An expression operated on by logical NOT, logical AND, or logical OR</p>
</li>

<li>
<p>The second expression of a <b>for</b> statement</p>
</li>

<li>
<p>The expression of an <b>if</b> statement</p>
</li>

<li>
<p>The expression of the <b>while</b> clause in either a <b>while</b> or <b>do</b>... <b>while</b> statement</p>
</li>

<li>
<p>An expression used as a pattern (as in Overall Program Structure)</p>
</li>
</ul>

<p>All arithmetic shall follow the semantics of floating-point arithmetic as specified by the ISO&nbsp;C standard (see <a href=
"xcu_chap01.html#tag_01_07_02"><i>Concepts Derived from the ISO C Standard</i></a> ).</p>

<p>The value of the expression:</p>

<pre>
<i>expr1</i> <tt>^</tt> <i>expr2</i>
</pre>

<p>shall be equivalent to the value returned by the ISO&nbsp;C standard function call:</p>

<pre>
<tt>pow(</tt><i>expr1</i><tt>,</tt> <i>expr2</i><tt>)
</tt>
</pre>

<p>The expression:</p>

<pre>
<tt>lvalue ^=</tt> <i>expr</i>
</pre>

<p>shall be equivalent to the ISO&nbsp;C standard expression:</p>

<pre>
<tt>lvalue = pow(lvalue,</tt> <i>expr</i><tt>)