http://www.tcl.tk/man/tcl8.5/TclCmd/time.htm 



Executes ''script'' and reports how long it takes per iteration (if ''iterations'' is absent, only one iteration is used). From 8.5, the report has sub-microsecond resolution (with accuracy depending on the OS's available timers).

<<discussion>>
** Description **
Does anyone have some examples of using [Tcl]'s time command?
'''`time`''' executes ''script'' one time, or optionally, ''iterations'' times,
time {myCommand $arg1 $arg2} 1000
 time {myCommand $arg1 $arg2} 1000

will run the specified command, with substitutions performed, 1000 times, and finally return a list like this:

The higher you give the factor, the more precise the measurement will be, but of course take proportional time - so best start with small values, and increase until it feels too slow.

See [How to measure Performance] for additional info - but no obvious examples.
More iterations increase the precision of the returned value, at the cost of
----
Also another use of the word ''time'' is as a network protocol for the transmission of time data - see RFC868 [http://www.faqs.org/rfcs/rfc868.html]
[NTP] is a more sophisticated protocol, but the time protocol does a simple job simply.

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In yet another different use of the word '''time''', [LV] asks "Has anyone written a ''time'' chooser similar to the date chooser widgets written elsewhere on the Wiki?" Larry refers to [A little date chooser] and [An i15d date chooser].
You can measure the runtime of a lengthy script with the following pattern:
You might like to check out: [timeentry] and [timefield].

----

======
set t0 [clock clicks -millisec]
 set t0 [clock clicks -millisec]
 ...
 ...
 puts stderr "[expr ([clock clicks -millisec]-$t0)/1000.] sec" ;# RS

[kbk], Tcl's own wizard of speed and time,  has done all the work to ensure
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Even when you're not interested in the timing, you can use [time] as a simple control structure for loops:

proc measure args {
 time {puts Hello} 5

Use it like this:

======
for {set i 0} {$i<5} {incr i} {puts Hello}
 for {set i 0} {$i<5} {incr i} {puts Hello}

([MS] voip in the [Tcl chatroom] 2005-03-03, brought here by [RS])


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[LV] Sometimes users ask how to get a tcl program's time in terms of real/user/system, similar to how they would use the ksh built in time command.

----


"`time` has more looping overhead than a script version!  See below for proof."
"[[time]] has more looping overhead than a script version!  See below for proof."
======
proc f {} {}

proc a {} {
    set n 100000
    puts [time f $n]

    set c $n
    incr c
    set start [clock microseconds]
    while {[incr c -1]} {
        f
    }
    set end [clock microseconds]

    puts "[expr {($end - $start)/double($n)}] microseconds per iteration"
}

a
======

On my machine (WinXP, Tcl 8.6b1.2), this produces the following times:

======
3.78325 microseconds per iteration
1.62831 microseconds per iteration
======

`f` is run 100,000 times, both by `time` and by `[while]`/`[incr]`.  Strangely enough, it takes `time` more than twice as long as `while` to do this.  That makes no sense.  Maybe `time` is recompiling the script `f` each time.  But, how long can it take to compile a script that's only '''one character long'''???
[[f]] is run 100,000 times, both by [[time]] and by [[[while]]]/[[incr]]].  Strangely enough, it takes [[time]] more than twice as long as [[while]] to do this.  That makes no sense.  Maybe [[time]] is recompiling the script "f" each time.  But, how long can it take to compile a script that's only '''one character long'''???

<<discussion>>

**A stabilized timing helper**
[DKF]: It's not always easy to pick a good number of iterations to run the timing script for. This script picks a balance by trying to use the number of iterations that would take about 2 seconds (subject to it being a minimum of 500 iterations).
======
proc measure args {
    set it [expr {int(ceil(10000./[lindex [time $args] 0]))}]
    set it [expr {int(ceil(2000000./[lindex [time $args $it] 0]))}]
    while {$it < 500} {set it 500}
    lindex [time $args $it] 0
}
======
Use it like this:
======
measure theProc arg1 arg2...
======
Adapting to take a single script argument instead is trivial.
** See Also **
<<categories>> Tcl syntax | Arts and crafts of Tcl-Tk programming | Command | Performance | Internet