Printing on screen the percentage completed while my tcl script is running?

Question

I have a tcl script which takes a few minutes to run (the execution time varies based on different configurations).

I want the users to have some kind of an idea of whether it's still executing and how long it would take to complete while the script executes.

Some of the ideas I've had so far:

1) Indicate it using ... which keep increasing with each internal command run or so. But again it doesn't really give a sense of how much more to go for a first time user.

2) Use the revolving slash which I've seen used many places.

3) Have an actual percentage completed output on screen. No idea if this is viable or how to go about it.

Does anyone have any ideas on what could be done so that users of the script understand what's going on and how to do this?

Also if I'm implementing it using ... , how do I get them to print the . on the same line each time. If I use puts to do this in the tcl script the . just gets printed on the next line.

And for the revolving slash, I would need to replace something which was already printed on screen. How can I do this with tcl?

I tried using the -nonewline option with puts. But that just printed out all the dots together at the end of the script rather than one by one during execution. This is what I had tried puts -nonewline "." — egorulz, Dec 12 '12 at 09:15

score 2 · Accepted Answer · answered Dec 12 '12 at 10:07

First off, the reason you were having problems printing dots was that Tcl was buffering its output, waiting for a new line. That's often a useful behavior (often enough that it's the default) but it isn't wanted in this case so you turn it off with:

fconfigure stdout -buffering none

(The other buffering options are line and full, which offer progressively higher levels of buffering for improved performance but reduced responsiveness.) Alternatively, do flush stdout after printing a dot. (Or print the dots to stderr, which is unbuffered by default due to mainly being for error messages.)

Doing a spinner isn't much harder than printing dots. The key trick is to use a carriage return (a non-printable character sometimes visualized as ^M) to move the cursor position back to the start of the line. It's nice to factor the spinner code out into a little procedure:

proc spinner {} {
    global spinnerIdx
    if {[incr spinnerIdx] > 3} {
        set spinnerIdx 0
    }
    set spinnerChars {/ - \\ |}
    puts -nonewline "\r[lindex $spinnerChars $spinnerIdx]"
    flush stdout
}

Then all you need to do is call spinner regularly. Easy! (Also, print something over the spinner once you've finished; just do puts "\r$theOrdinaryMessage".)

Going all the way to an actual progress meter is nice, and it builds on these techniques, but it requires that you work out how much processing there is to do and so on. A spinner is much easier to implement! (Especially if you've not yet nailed down how much work there is to do.)

Use the backspace character `\b` instead of carriage return if you don't want the spinner (or a percentage or something else) at the very beginning of the line. — potrzebie, Dec 12 '12 at 10:16
FWIW, I got this trick in passing from the creator of SQLite… — Donal Fellows, Dec 12 '12 at 13:43

potrzebie · Answer 2 · 2012-12-12T10:24:56.843

The standard output stream is initially line buffered, so you won't see new output until you write a newline character, call flush or close it (which is automatically done when your script exits). You could turn this buffering off with...

fconfigure stdout -buffering none

...but diagnostics, errors, messages, progress etc should really be written to the stderr stream instead. It has buffering set to none by default so you won't need fconfigure.

Printing on screen the percentage completed while my tcl script is running?

2 Answers2