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<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12"> 
#!/usr/bin/tclsh
#
# Demonstrate global variables
# and backslash substitution
 
if {$argc &gt;= 1} {
    set N 1
    foreach Arg $argv {
        puts stdout "$N: $Arg\n"
        set N [expr $N + 1]
        if {$Arg == "ring"} {
            puts stdout "\a"
        }
    }
} else {
    puts stdout "$argv0 on \
        X Display $env(DISPLAY)\n"
}

***
~/tcltk$ <b>./hello3.tcl</b>
./hello3.tcl on  X Display :0.0
 
~/tcltk$ <b>./hello3.tcl ring</b>
1: ring
			</code>
</pre>
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>Tcl global variables and backslash substitutions</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 3 页（共15 页）</nobr></font></td>
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<p>Several global variables exist (and are pre-defined, 
				if not null in the current context) when a Tcl/Tk 
				script begins running. These variables permit access to the 
				operating environment as follows: <i>argc</i> is the count of 
				arguments to the script, not counting the name as invoked. 
				<i>argv</i> is a list (not an array) of arguments. <i>argv0</i> is the 
				invoked filename (which may be a symlink). <i>env</i> is an 
				array that is indexed by the names of the current shell's 
				environment variables. <i>errorCode</i> stores information 
				about the most recent Tcl error, while <i>errorInfo</i> contains 
				a stack trace from the same event. The list goes on with another
				dozen <i>tcl_xxx</i> variables from 
				<code>tcl_interactive</code> to <code>tcl_version</code>.
				A good summary is found in <i>Tcl/Tk in a Nutshell</i> (see 
				the Resources at the end of this tutorial for more information).</p>
<p>Several of these variables are used in the sample code at left, along with (once 
				again) some backslash-quoted characters, \n and \a.
				<code><b>\</b><i>char</i></code> allows substitution of non-printing 
				ASCII characters. This is common to many scripting and shell 
				environments under UNIX. As noted in the table, a backslash-quoted 
				character that has no defined substitution is simply echoed to output.</p>
<table border="1">
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<th align="center" width="150pt">\<i>character</i></th><th align="center" width="150pt">Substitution</th>
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<td width="150pt"><b>\a</b></td><td width="150pt">Bell</td>
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<td width="150pt"><b>\b</b></td><td width="150pt">Backspace</td>
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<td width="150pt"><b>\f</b></td><td width="150pt">Formfeed</td>
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<td width="150pt"><b>\n or \newline</b></td><td width="150pt">Newline</td>
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<td width="150pt"><b>\r</b></td><td width="150pt">Carriage return</td>
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<td width="150pt"><b>\t</b></td><td width="150pt">Horizontal tab</td>
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<td width="150pt"><b>\v</b></td><td width="150pt">Vertical Tab</td>
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<td width="150pt"><b>\space ("\ ")</b></td><td width="150pt">Space</td>
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<td width="150pt"><b>\<i>ddd</i></b></td><td width="150pt">Octal value</td>
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<td width="150pt"><b>\x<i>ddd</i>...</b></td><td width="150pt">Hexadecimal value</td>
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<td width="150pt"><b>\c</b></td><td width="150pt">Echo 'c'</td>
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<td width="150pt"><b>\\</b></td><td width="150pt">Backslash</td>
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