time(n) Tcl Built-In Commands time(n)

time - Time the execution of a script

time script ?count?

This command will call the Tcl interpreter count times to evaluate script (or once if count is not specified). It will then return a string of the form
503.2 microseconds per iteration

which indicates the average amount of time required per iteration, in microseconds. Time is measured in elapsed time, not CPU time.

Estimate how long it takes for a simple Tcl for loop to count to a thousand:
time {
    for {set i 0} {$i<1000} {incr i} {
        # empty body


script, time