 the previous example.</P>


<H2 CLASS="HeadingC">
Command Substitution</H2>
<P>
If an open bracket occurs in any of the fields of a command, then command substitution occurs. All of the text up to the matching close bracket is treated as a Tcl command and executed immediately. The result of that command is substituted for the bracketed text. For example, consider the command:</P>
<PRE>var a [var b]</PRE>
<P>
When the <CODE>
var</CODE>
 command has only a single argument, it is the name of a variable and <C