TCL upvar command usage

upvar, a built-in Tcl command, links a variable to some other variable at the specified level of evaluation.

i.e If you want to change the value of variable from with in the procedure we can use upvar to do that.

Example:

proc upvar_demo {var1 var2} {

upvar $var1 procvar1

upvar $var2 procvar2

set procvar1 TCL

set procvar2 Script

}

set outvar1 Hello

set outvar2 World

puts "Values of variables before executing the procedure"

puts "outvar1 : $outvar1"

puts "outvar2 : $outvar2"

upvar_demo outvar1 outvar2

puts "Values of variables after executing the upvar procedure"

puts "outvar1 : $outvar1"

puts "outvar2 : $outvar2"

#Output :

Values of variables before executing the procedure

outvar1 : Hello

outvar2 : World

Values of variables after executing the upvar procedure

outvar1 : TCL

outvar2 : Script