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关于嵌入式编程的tcl语法的资料

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<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
~/tcltk$ <b>tclsh</b>
% <b>nslookup orbdesigns.com</b>
Server:         192.168.1.3
Address:        192.168.1.3#53
 
Name:   orbdesigns.com
Address: 64.81.69.163
 
% <b>set d [date]</b>
Sun Mar 25 13:51:59 PST 2001
% <b>puts stdout $d</b>
 
% <b>set d [exec date]</b>
Sun Mar 25 13:52:19 PST 2001
% <b>puts stdout $d</b>
Sun Mar 25 13:52:19 PST 2001

******

% <b>if [catch {open foo r} Chan] {
    puts stdout "Sorry, Dave...\n"
}</b>
% <b>gets $Chan</b>
One
% <b>gets $Chan</b>
Two
% <b>eof $Chan</b>
0
% <b>close $Chan</b>
%
			</code>
</pre>
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>Tcl 进程和文件 I/O</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 14 页（共15 页）</nobr></font></td>
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<p>
						
<i>exec</i> 命令用于显式地执行外部命令。在 Linux 下，当 Tcl 处于交互方式时，可以直接运行大多数外部命令，如左边示例所示。用 <i>exec</i> 运行时，会将程序的 stdout 输出返回到 Tcl，而不是返回到屏幕，这允许将数据赋值给变量。当程序在后台启动时，立即返回的值是程序的 PID。<i>exec</i> 程序可以充分利用 UNIX 环境中的 I/O 重定向和管道。</p>
<p>其它进程命令有 <i>exit</i>（终止正在运行的 Tcl 脚本）和 <i>pid</i>（返回当前或指定进程的 PID），对于出于各种目的的情况，这非常便利。Tcl 不合并任何本机进程控制命令，但可以将 exec 命令与 PID 数据一起使用来实现许多任务。</p>
<p>文件操纵使用下列命令：<i>open</i>、<i>close</i>、<i>gets</i>、<i>puts</i>、<i>read</i>、<i>tell</i>、<i>seek</i>、<i>eof</i> 和 <i>flush</i>。如左边所示，在文件打开命令期间 <i>catch</i> 命令对错误检查是有用的。当在遇到新的一行字符之前需要打印程序输出时，如在用户数据提示符中，使用 <i>flush</i> 来写输出缓冲区。</p>
<p>另外一个功能（在受支持的环境中）是以打开文件的方式打开管道的能力。例如，用 <i>set Channel	[open "|sort foobar" r]</i> 打开管道通道后，第一个 <i>gets</i> 的输出将是&ldquo;Eight&rdquo;（文件数据&ldquo;One&rdquo;到&ldquo;Ten&rdquo;的输出在 10 个单独的行上按字母顺序排列）。</p>
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