perl3.htm

Perl作为一门重要的工程语言

              .=可在一个赋值语句中出现多次，如：<br>
              &nbsp;&nbsp;$value1 = $value2 = &quot;a string&quot;;<br>
              .=作为子表达式<br>
              &nbsp;&nbsp;($a = $b) += 3;<br>
              &nbsp;&nbsp;等价于<br>
              &nbsp;&nbsp;$a = $b;<br>
              &nbsp;&nbsp;$a += 3;<br>
              &nbsp;&nbsp;但建议不要使用这种方式。<br>
              <a name=七、自增自减操作符>七、自增自减操作符</a> ：++、--(与C++中的用法相同)<br>
              .不要在变量两边都使用此种操作符：++$var-- # error<br>
              .不要在变量自增/减后在同一表达式中再次使用：$var2 &nbsp;&nbsp;= $var1 + ++$var1; # error<br>
              .在PERL中++可用于字符串，但当结尾字符为'z'、'Z'、'9'时进位，如：<br>
              &nbsp;&nbsp;$stringvar = &quot;abc&quot;;<br>
              &nbsp;&nbsp;$stringvar++; # $stringvar contains &quot;abd&quot; 
              now<br>
              <br>
              &nbsp;&nbsp;$stringvar = &quot;aBC&quot;;<br>
              &nbsp;&nbsp;$stringvar++; # $stringvar contains &quot;aBD&quot; 
              now<br>
              <br>
              &nbsp;&nbsp;$stringvar = &quot;abz&quot;;<br>
              &nbsp;&nbsp;$stringvar++; # $stringvar now contains &quot;aca&quot;<br>
              <br>
              &nbsp;&nbsp;$stringvar = &quot;AGZZZ&quot;;<br>
              &nbsp;&nbsp;$stringvar++; # $stringvar now contains &quot;AHAAA&quot;<br>
              <br>
              &nbsp;&nbsp;$stringvar = &quot;ab4&quot;;<br>
              &nbsp;&nbsp;$stringvar++; # $stringvar now contains &quot;ab5&quot;<br>
              <br>
              &nbsp;&nbsp;$stringvar = &quot;bc999&quot;;<br>
              &nbsp;&nbsp;$stringvar++; # $stringvar now contains &quot;bd000&quot;<br>
              .不要使用--，PERL将先将字符串转换为数字再进行自减<br>
              &nbsp;&nbsp;$stringvar = &quot;abc&quot;;<br>
              &nbsp;&nbsp;$stringvar--; # $stringvar = -1 now<br>
              <br>
              .如果字符串中含有非字母且非数字的字符，或数字位于字母中，则经过++运算前值转换为数字零，因此结果为1，如：<br>
              &nbsp;&nbsp;$stringvar = &quot;ab*c&quot;;<br>
              &nbsp;&nbsp;$stringvar++;<br>
              &nbsp;&nbsp;$stringvar = &quot;ab5c&quot;;<br>
              &nbsp;&nbsp;$stringvar++;<br>
              <a name=八、字符串联结和重复操作符>八、字符串联结和重复操作符</a><br>
              &nbsp;&nbsp;联接: .<br>
              &nbsp;&nbsp;重复：x<br>
              &nbsp;&nbsp;联接且赋值(类似+=)： .=<br>
              例：<br>
              &nbsp;&nbsp;$newstring = &quot;potato&quot; . &quot;head&quot;;<br>
              &nbsp;&nbsp;$newstring = &quot;t&quot; x 5;<br>
              &nbsp;&nbsp;$a = &quot;be&quot;;<br>
              &nbsp;&nbsp;$a .= &quot;witched&quot;; # $a is now &quot;bewitched&quot;<br>
              <a name=九、逗号操作符>九、逗号操作符</a><br>
              &nbsp;&nbsp;其前面的表达式先进行运算，如：<br>
              &nbsp;&nbsp;$var1 += 1, $var2 = $var1;<br>
              &nbsp;&nbsp;等价于<br>
              &nbsp;&nbsp;$var1 += 1;<br>
              &nbsp;&nbsp;$var2 = $var1;<br>
              &nbsp;&nbsp;使用此操作符的唯一理由是提高程序的可读性，将关系密切的两个表达式结合在一起，如：<br>
              &nbsp;&nbsp;$val = 26;<br>
              &nbsp;&nbsp;$result = (++$val, $val + 5); # $result = 32<br>
              &nbsp;&nbsp;注意如果此处没有括号则意义不同：<br>
              &nbsp;&nbsp;$val = 26;<br>
              &nbsp;&nbsp;$result = ++$val, $val + 5; # $result = 27<br>
              <a name=十、条件操作符>十、条件操作符</a><br>
              &nbsp;&nbsp;与C中类似，条件?值1:值2，当条件为真时取值1，为假时取值2，如：<br>
              &nbsp;&nbsp;$result = $var == 0 ? 14 : 7;<br>
              &nbsp;&nbsp;$result = 43 + ($divisor == 0 ? 0 : $dividend / $divisor);<br>
              &nbsp;&nbsp;PERL 5中，还可以在赋值式左边使用条件操作符来选择被赋值的变量，如：<br>
              &nbsp;&nbsp;$condvar == 43 ? $var1 : $var2 = 14;<br>
              &nbsp;&nbsp;$condvar == 43 ? $var1 = 14 : $var2 = 14;<br>
              <a name=十一、操作符的次序>十一、操作符的次序</a><br>
              <br>
            </p>
            <p align=center><b>Table 3.6.</b> 操作符次序</p>
            <div align=center>
              <center>
                <table border=1 width=65%>
                  <tr>
                    <td valign=top width=214><b>操作符</b></td>
                    <td valign=top width=310><b>描述</b></td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>++</tt>, <tt>--</tt></td>
                    <td valign=top width=310>自增，自减</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>-</tt>, <tt>~</tt>, <tt>!</tt></td>
                    <td valign=top width=310>单目</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>**</tt></td>
                    <td valign=top width=310>乘方</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>=~</tt>, <tt>!~</tt></td>
                    <td valign=top width=310>模式匹配</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>*</tt>, <tt>/</tt>, <tt>%</tt>, 
                      <tt>x</tt></td>
                    <td valign=top width=310>乘，除，取余，重复</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>+</tt>, <tt>-</tt>, <tt>.</tt></td>
                    <td valign=top width=310>加，减，联接</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>&lt;&lt;</tt>, <tt>&gt;&gt;</tt></td>
                    <td valign=top width=310>移位</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>-e</tt>, <tt>-r</tt>, etc.</td>
                    <td valign=top width=310>文件状态</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>&lt;</tt>, <tt>&lt;=</tt>, <tt>&gt;</tt>, 
                      <tt>&gt;=</tt>, <tt>lt</tt>, <tt>le</tt>, <tt>gt</tt>, <tt>ge</tt></td>
                    <td valign=top width=310>不等比较</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>==</tt>, <tt>!=</tt>, <tt>&lt;=&gt;</tt>, 
                      <tt>eq</tt>, <tt>ne</tt>, <tt>cmp</tt></td>
                    <td valign=top width=310>相等比较</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>&amp;</tt></td>
                    <td valign=top width=310>位与</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>|</tt>, <tt>^</tt></td>
                    <td valign=top width=310>位或，位异或</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>&amp;&amp;</tt></td>
                    <td valign=top width=310>逻辑与</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>||</tt></td>
                    <td valign=top width=310>逻辑或</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>..</tt></td>
                    <td valign=top width=310>列表范围</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>?</tt> and <tt>:</tt></td>
                    <td valign=top width=310>条件操作符</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>=</tt>, <tt>+=</tt>, <tt>-=</tt>, 
                      <tt>*=</tt>,</td>
                    <td valign=top width=310>赋值</td>
                  </tr>
                  <tr>
                    <td valign=top width=214>and so on</td>
                    <td valign=top width=310>　</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>,</tt></td>
                    <td valign=top width=310>逗号操作符</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>not</tt></td>
                    <td valign=top width=310>Low-precedence logical NOT</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>and</tt></td>
                    <td valign=top width=310>Low-precedence logical AND</td>
                  </tr>
                  <tr>
                    <td valign=top width=214><tt>or</tt>, <tt>xor</tt></td>
                    <td valign=top width=310>Low-precedence logical OR and XOR</td>
                  </tr>
                </table>
              </center>
            </div>
            <p>.操作符结合性(associativity)：<br>
            </p>
            <p align=center><b>Table 3.7. 操作符结合性</b></p>
            <div align=center>
              <center>
                <table border=1 width=65%>
                  <tr>
                    <td valign=top width=240><b>操作符</b></td>
                    <td valign=top width=240><b>结合性</b></td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>++</tt>, <tt>--</tt></td>
                    <td valign=top width=240>无</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>-</tt>, <tt>~</tt>, <tt>!</tt></td>
                    <td valign=top width=240>Right-to-left</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>**</tt></td>
                    <td valign=top width=240>Right-to-left</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>=~</tt>, <tt>!~</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>*</tt>, <tt>/</tt>, <tt>%</tt>, 
                      <tt>x</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>+</tt>, <tt>-</tt>, <tt>.</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>&lt;&lt;</tt>, <tt>&gt;&gt;</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>-e</tt>, <tt>-r</tt>,</td>
                    <td valign=top width=240>无</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>&lt;</tt>, <tt>&lt;=</tt>, <tt>&gt;</tt>, 
                      <tt>&gt;=</tt>, <tt>lt</tt>, <tt>le</tt>, <tt>gt</tt>, <tt>ge</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>==</tt>, <tt>!=</tt>, <tt>&lt;=&gt;</tt>, 
                      <tt>eq</tt>, <tt>ne</tt>, <tt>cmp</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>&amp;</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>|</tt>, <tt>^</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>&amp;&amp;</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>||</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>..</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>?</tt> and <tt>:</tt></td>
                    <td valign=top width=240>Right-to-left</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>=</tt>, <tt>+=</tt>, <tt>-=</tt>, 
                      <tt>*=</tt>,</td>
                    <td valign=top width=240>Right-to-left</td>
                  </tr>
                  <tr>
                    <td valign=top width=240>and so on</td>
                    <td valign=top width=240>　</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>,</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>not</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>and</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                  <tr>
                    <td valign=top width=240><tt>or</tt>, <tt>xor</tt></td>
                    <td valign=top width=240>Left-to-right</td>
                  </tr>
                </table>
              </center>
            </div>
            <p><br>
              <br>
              建议：<br>
              &nbsp;&nbsp;1、当你不确定某操作符是否先执行时，一定要用括号明确之。<br>
              &nbsp;&nbsp;2、用多行、空格等方式提高程序的可读性。<br>
            </p>
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