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<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
#!/usr/bin/tclsh
#
# Demonstrate procedures and
# global scoping briefly

set PI [expr 2 * asin(1.0)]
 
proc circum {rad} {
	global PI
	return [expr 2.0 * $rad * $PI]
}
 
proc c_area {rad} {
	global PI
	return [expr $rad * $rad * $PI]
}
 
set rad 3
 
puts stdout "Area of circle of\
radius $rad is [c_area $rad],\n\
the circumference is\
[circum $rad].\n"

*********
~/tcltk$ <b>./protest.tcl</b>
Area of circle of radius 3 is 28.2743338823,
 the circumference is 18.8495559215.
			</code>
</pre>
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>Tcl procedures</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 10 页（共15 页）</nobr></font></td>
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<p>The <i>proc</i> command defines a Tcl procedure. Once 
				defined, a procedure can be called or used just as a 
				built-in Tcl command would be. Additionally, parameters 
				can be defined with default values; for example, changing 
				the definition at the left to read 
				<code>proc c_area { {rad 1} } </code> would enable the 
				c_area procedure to be called without parameters, returning 
				the area of the unit circle.</p>
<p>The <i>rename</i> command is used just as it sounds, to give a new 
				name to an existing command or procedure. There are two 
				distinct reasons for using rename. The first is to add 
				functionality to an existing command by renaming the original, 
				then replacing it with a procedure of the same name. The 
				procedure can call the original, and add whatever bells and 
				whistles are necessary. The second reason for rename is to 
				map a command out of existence, like 
				<code>rename exec {};</code>, for example, to prevent users 
				from executing external commands.</p>
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