executing an m-file using a string for calling

Hello, I am trying to find a way to execute an m-file from a string.

For example I get from a DB return the name myfunc(1,2) as a char and I want to execute the function myfunc.m with the (1,2) as variables. Does anyone have any solution.

Thanx in advance.

Georgios Mavropoulos

Answer 1

[Walter Roberson]

%somehow before this, DBString = 'myfunc(1,2)'

eval(DBString)

[Jan]

Although I find arguments against EVAL every day, it is the most exact answer here. +1

[Walter Roberson]

There are other possibilities, such as parsing out the arguments and turning them in to a cell array of numbers, and extracting the function name string, and then using feval(FunctionNameString, Args{:})

[Hayatullahi Adeyemo]

Thanks for this answer. It just solved my long-term problem

[Mathijs Franssen]

Dear Jan, given your statement 'Although I find arguments against EVAL every day, it is the most exact answer here. +1', is there any other option nowadays or could you kindly elaborate on the arguments against using eval? Many thanks in advance!

[Stephen23]

"...is there any other option nowadays..."

There have always been better options, not just "nowadays".

The fundamental flaw in the original question was not adressed in the thread so far, but is due to the poor data design: storing a function and its inputs in one string. Better data design would store its inputs as data in their own right (which is anyway simpler, is more efficient, and avoids superfluous, slow, lossy data type conversion). Then calling the function/script is trivial with one str2func call and then more efficient calling of the function handle thereafter.

"...could you kindly elaborate on the arguments against using eval?"

In this particular example, repeated calls to eval this string will likely be less efficient than repeated calls to the equivalent function handle (MATLAB's JIT compiler has no way to optimize the code hidden in a string, but it certainly can with a properly defined function handle called with properly defined input arguments).

On top of this we have the usual problems of disabling the static code analysis (which means no syntax checking, no tracing variables, no code hints, no tab completion, no input hints, no variable highlighting, etc.), makes debugging harder, is a security risk, and various other points that have been discussed many times before (quite easy to find by searching this forum).

[Mathijs Franssen]

Excellent, thanks a million Stephen! Wasn't aware of str2func, first time I've ran into this sort of issue. This helps!

[Jürgen]

for me 'Stephens comment' of 28th,jan. 2021 should be worked out more compact and moved to the top-rated answer to the question.

I was also searching for something like (list of) function reference defined during runtime.

The str2fun seems the way to go with respect to all the points in Stephens comment (code analysis, syntax checking, tracing variables, code hints, tab completion, input hints, variable highlighting, debugging, security).

Answer 2

[Jan]

If you call RUN with a string, which contains the path, the file extension .m is removed. Without the path, .m is kept.

mfile = dir('layer*.m');
[trash, name] = fileparts(mfile(1).name);
run(name);

Or:

mfile = dir('layer*.m');
run(fullfile(cd, mfile(1).name));

Note: "mfile(1)" considers, that DIR can find multiple matching files.

[Dimitris]

That worked. Thanks! :)

Answer 3

[Georgios Mavropoulos]

thank you Walter, I tried both of your suggestions and they both worked.

Thanks again for the help.

Answer 4

[Dimitris]

I'm trying to do something similar. My output is an .m file. Like this:

mfile = dir('layer*.m')

So, afterwards I want to run the file named layer<something>.m But if I do as you say:

eval(mfile.name)

I get this error:

??? Undefined variable "layer2" or class "layer2.m".

Why is this happening? The file I'm trying to run, layer2.m, is in the current directory.

[Walter Roberson]

You have to remove the .m suffix before you can eval()

As you do not appear to be sending input or expecting output, it is plausible that you are using scripts instead of functions. If so, then consider using run(), as that will remove the .m for you.

[Jan]

RUN removes the file extension only, if the name contains the path:

working: run('C:\MFiles\layer2.m')

failing: run('layer2.m')

I think, this is a bug in RUN: If "script" does not contain a path, "exist(script, 'file')" checks the existence before "evalin('caller', [script, ';'])". But if "script" is an existing file, the file extension let EVALIN fail. "evalin('caller', [s, ';'])" would work. (checked in 2009a)

[Jan]

Bug report is submitted.

Answer 5

[Dimitris]

I tried to use:

run(mfile.name)

but I got the same error:

??? Undefined variable "layer2" or class "layer2.m".

Error in ==> run at 74
    evalin('caller',[script ';']);

:S I also tried

run(eval(mfile.name))

with the same results... Thank you for your interest!

[Hayatullahi Adeyemo]

You can try using

    eval(mfile.name)

[Jan]

@Hayatullahi Adeyemo: The variable "mfile.name" contains the string 'layer2'. The error message produced by run('layer2') means, that there is no function with this name in Matlab's path. Then eval('layer2') will not work also.