How to use who within eval

Here is the code:

file_name = 'test';
eval(['file_length = length(who(''-file'',' file_name '));']);

But this doesn't work, because who requires a quoted string as a variable. Then I tried this,

eval(['file_length = length(who(''-file'', ''file_name'' ));']);

It didn't work, apparently. Now file_name showed up instead of the value I put in it. This sounds a very simple question, but I just don't know what to do. Help!

Answer 1

[Andrew Newell]

This is a working example:

clear
x = zeros(10,1); y = x;
save matlab.mat
file_name='matlab.mat';
eval('file_length = length(who(''-file'',file_name))')

file_length =

     2

EDIT: Although I answered the question you asked, I agree with Sean and the Cyclist that it would be better not to use eval. See Loren's blog for some reasons.

[Qianyu]

Thank you. That worked. The reason I use eval is because this is a loop, and a series of files will go through the loop. I escaped the loop part so I didn't have to type many lines. Sorry for the unclarity.

[Andrew Newell]

Actually, the Cyclist's solution would also work nicely in a loop.

[the cyclist]

For example, even if you need the value of the looping variable in the file name, you can often use num2str() to convert the numeric to a string, and append it to the file name.

Answer 2

[Sean de Wolski]

Why use eval? Nothing in that statement looks like it couldn't be done without it.

Answer 3

[the cyclist]

Agree with Sean that you do not need eval() here. Try this:

 file_name = 'test';
 file_length = length(who('-file',file_name));