How do I overwrite text in the command window?

Question

Kyle Poe 2017-7-10

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回答： Cristi Savlovschi 2021-7-15

I am trying to write a counter that uses the format "processing subject ### of 123", where the ### changes in the command window upon every subject change. I know this could be accomplished in a loop with something like

 fprintf('processing subject 000 of 123')
 for number in 1:123
    fprintf('\b\b\b\b\b\b\b\b\b\b%s of 123',subnum(number)) 
    % subnum is a 3-digit number in character form to preserve the 3-digit format declared elsewhere
 end

But that is ugly and terribly inefficient. How do I rectify the problem?

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Answer 1

Walter Roberson 2017-7-10

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That is the most efficient way. There is no way to address individual characters or pixels of the command output window (unless perhaps you can get at it from the java level.)

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dpb 2017-7-10

And, \r is interpreted same as \n so that doesn't help, either.

But, might consider either a waitbar or just a msgbox

Kyle Poe 2017-7-10

Ah. Oh well. Thank you anyway!

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Answer 2

Eeshan Bhatt 2018-10-25

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编辑：Eeshan Bhatt 2018-10-25

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I know you have an accepted answer, but here's a quick robust code that I use often.

nbytes = fprintf('processing 0 of %d', length(z));
for nz = z
    while nbytes > 0
         fprintf('\b')
         nbytes = nbytes - 1;
    end
  nbytes = fprintf('processing %d of %d', nz, length(z));
  % YOUR PROCESS HERE
  %
  %
  %
end

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Ted Shultz 2019-7-19

编辑：Ted Shultz 2019-7-19

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Eeshan, this is a nice solution! I would propose this small modification so that it runs a little faster, and is a little simpler:

nbytes = fprintf('processing 0 of %d', length(z));
for nz = z
    fprintf(repmat('\b',1,nbytes))
    nbytes = fprintf('processing %d of %d\n', nz, length(z));
      % YOUR PROCESS HERE
      %
      %
      %
end

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Answer 3

Fangjun Jiang 2017-7-10

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or go fancy, waitbar()

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Kyle Poe 2017-7-11

This is what I ended up using, thank you!

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Answer 4

Boubat Matthieu 2020-7-28

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I packaged the use of fprintf('\b') into a class hoping that it will ease the way to rewrite/update text in the command window. If you want to give it a try it's available here.

It goes like this:

prefix = 'processing subject ';
suffix = ' of 123';
progression = UpdatableText(prefix,suffix); % UpdatableText is the actual class
for i = 1:123
    progression.print(num2str(i));
end

There are also methods to easily add a percent value and a progress bar.

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Answer 5

Cristi Savlovschi 2021-7-15

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function dispProgressMsg(msg)
ASCII_BKSP_CHAR = 8;
persistent prevMsgLen;
if isempty(prevMsgLen) 
    prevMsgLen = 0;
end
    
disp([ char(repmat(ASCII_BKSP_CHAR,1,prevMsgLen)) msg]);
prevMsgLen = numel(msg)+1;