man append () - Append to variable
NAME
append - Append to variable
SYNOPSIS
append varName ?value value value ...?
DESCRIPTION
Append all of the value arguments to the current value of variable varName. If varName doesn't exist, it is given a value equal to the concatenation of all the value arguments. The result of this command is the new value stored in variable varName. This command provides an efficient way to build up long variables incrementally. For example, ``append a $b'' is much more efficient than ``set a $a$b'' if $a is long.
EXAMPLE
Building a string of comma-separated numbers piecemeal using a loop. set var 0 for {set i 1} {$i<=10} {incr i} { append var "," $i } puts $var # Prints 0,1,2,3,4,5,6,7,8,9,10
SEE ALSO
KEYWORDS
append, variable