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+'\"
+'\" Copyright (c) 1993 The Regents of the University of California.
+'\" Copyright (c) 1994-1997 Sun Microsystems, Inc.
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\" 
+'\" SCCS: @(#) upvar.n 1.16 97/08/13 13:43:34
+'\" 
+.so man.macros
+.TH upvar n "" Tcl "Tcl Built-In Commands"
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+upvar \- Create link to variable in a different stack frame
+.SH SYNOPSIS
+\fBupvar \fR?\fIlevel\fR? \fIotherVar myVar \fR?\fIotherVar myVar \fR...?
+.BE
+
+.SH DESCRIPTION
+.PP
+This command arranges for one or more local variables in the current
+procedure to refer to variables in an enclosing procedure call or
+to global variables.
+\fILevel\fR may have any of the forms permitted for the \fBuplevel\fR
+command, and may be omitted if the first letter of the first \fIotherVar\fR
+isn't \fB#\fR or a digit (it defaults to \fB1\fR).
+For each \fIotherVar\fR argument, \fBupvar\fR makes the variable
+by that name in the procedure frame given by \fIlevel\fR (or at
+global level, if \fIlevel\fR is \fB#0\fR) accessible
+in the current procedure by the name given in the corresponding
+\fImyVar\fR argument.
+The variable named by \fIotherVar\fR need not exist at the time of the
+call;  it will be created the first time \fImyVar\fR is referenced, just like
+an ordinary variable.  There must not exist a variable by the
+name \fImyVar\fR at the time \fBupvar\fR is invoked.
+\fIMyVar\fR is always treated as the name of a variable, not an
+array element.  Even if the name looks like an array element,
+such as \fBa(b)\fR, a regular variable is created.
+\fIOtherVar\fR may refer to a scalar variable, an array,
+or an array element.
+\fBUpvar\fR returns an empty string.
+.PP
+The \fBupvar\fR command simplifies the implementation of call-by-name
+procedure calling and also makes it easier to build new control constructs
+as Tcl procedures.
+For example, consider the following procedure:
+.CS
+\fBproc add2 name {
+	upvar $name x
+	set x [expr $x+2]
+}\fR
+.CE
+\fBAdd2\fR is invoked with an argument giving the name of a variable,
+and it adds two to the value of that variable.
+Although \fBadd2\fR could have been implemented using \fBuplevel\fR
+instead of \fBupvar\fR, \fBupvar\fR makes it simpler for \fBadd2\fR
+to access the variable in the caller's procedure frame.
+.PP
+\fBnamespace eval\fR is another way (besides procedure calls)
+that the Tcl naming context can change.
+It adds a call frame to the stack to represent the namespace context.
+This means each \fBnamespace eval\fR command
+counts as another call level for \fBuplevel\fR and \fBupvar\fR commands.
+For example, \fBinfo level 1\fR will return a list
+describing a command that is either
+the outermost procedure call or the outermost \fBnamespace eval\fR command.
+Also, \fBuplevel #0\fR evaluates a script
+at top-level in the outermost namespace (the global namespace).
+.PP
+.VS
+If an upvar variable is unset (e.g. \fBx\fR in \fBadd2\fR above), the
+\fBunset\fR operation affects the variable it is linked to, not the
+upvar variable.  There is no way to unset an upvar variable except
+by exiting the procedure in which it is defined.  However, it is
+possible to retarget an upvar variable by executing another \fBupvar\fR
+command.
+
+.SH BUGS
+.PP
+If \fIotherVar\fR refers to an element of an array, then variable
+traces set for the entire array will not be invoked when \fImyVar\fR
+is accessed (but traces on the particular element will still be
+invoked).  In particular, if the array is \fBenv\fR, then changes
+made to \fImyVar\fR will not be passed to subprocesses correctly.
+.VE
+
+.SH "SEE ALSO"
+namespace(n)
+
+.SH KEYWORDS
+context, frame, global, level, namespace, procedure, variable