The following examples of using Tcl can be tried in any application using Tcl, or, equivalently, in wish or tclsh, which are applications which come with the Tcl/Tk distribution and which do nothing else but run the Tcl interpreter. The % sign is the tcl command prompt and bold-face is used to represent the typed text.

% # comment
% set a 32
32
% set b 3.1415
3.1415
% set c "hi there"
hi there
% expr $a + $b
35.1415
% set d  [expr $a*3]
96
% puts "d=$d"
d=96
% while {$d > 0} { set d  [expr $d-20]; puts "d=$d" }
d=76
d=56
d=36
d=16
d=-4
% set text {d=$d}
d=$d
% for { set n 5} {$n>0} {set n [expr $n-1]} {
>  puts "n=$n"
>}
n=5
n=4
n=3
n=2
n=1
%

Usually the script will be contained in a text file which is then read using the source command:

% source foo

Procedures can also be easily defined in Tcl

% proc plus {a b} {
     return [expr $a+$b]
  }
% plus 2 2.3
4.3