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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>變量作用域規則</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 11 頁（共15 頁）</nobr></font></td>
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<p>作用域規則描述了過程和變量名以及值在程序的不同層次上的可見性。例如，在腳本的最外層定義的變量是全局變量。缺省情況下，全局變量是不可見的，在過程內部也不可用它們的值。這允許過程的編寫者自由地定義變量名并賦值，而不必擔心覆蓋對于局部作用域上未知的重要變量。要使全局變量在過程內部變得可見，必須將它聲明為<i>在過程內</i>，就象在上一屏的示例中，對 PI 使用 <i>global</i> 命令那樣。</p>
<p>
						
<i>upvar</i> 命令提供將局部變量與另一個作用域中變量的值相關聯的設施。這允許根據名稱將變量調用進過程，這對于當過程需要可以修改在另一個作用域的值而不僅僅使用它時，就顯得非常方便。這個命令語法是 <b>upvar <i>level $VarName LocalVar</i>
						</b>，其中 level 是到當前作用域之外的步驟數。&ldquo;#0&rdquo;表示全局作用域這一層。</p>
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