eval

Evaluate MATLAB expression

Syntax

eval(expression)

[output1,...,outputN] = eval(expression)

Description

eval(expression) evaluates the MATLAB^® code in expression.

Note

Security Considerations: When calling eval with untrusted user input, validate the input to avoid unexpected code execution. Examples of untrusted user input are data coming from a user you might not know or from a source you have no control over. If you need to address this concern, consider these approaches:

• Validate inputs to eval. First, search for allowed operations. Then, if you find other operations, disallow execution.

• Replace eval with an alternative. For more information, see Alternatives to the eval Function.

Performance Considerations: In most cases, using the eval function is also less efficient than using other MATLAB functions and language constructs, and the resulting code can be more difficult to read and debug. Consider using an alternative to eval.

[output1,...,outputN] = eval(expression) returns the outputs from expression in the specified variables.

Examples

Evaluate Expression

Use eval to evaluate and plot the expression magic(5).

Z = eval('magic(5)');
mesh(Z)

Input Arguments

expression — Expression to evaluate

character vector | string scalar

Expression to evaluate, specified as a character vector or string scalar. expression must be a valid MATLAB expression and must not include any MATLAB keywords. To determine whether a word is a MATLAB keyword, use the iskeyword function.

Example: eval('magic(5)')

Output Arguments

output1,...,outputN — Outputs from evaluated expression

any MATLAB data type

Outputs from evaluated expression, returned as any MATLAB data type.

Limitations

• If you use eval within an anonymous function, nested function, or function that contains a nested function, the evaluated expression does not create any variables.

Tips

• To allow the MATLAB parser to perform stricter checks on your code and avoid untrapped errors and other unexpected behaviors, do not include output arguments in the input to the eval function. For example, the statement eval(['output = ',expression]) is not recommended.

  Instead, specify output arguments to the eval function to store the results of the evaluated expression. For example:

    output = eval(expression)

Compatibility Considerations

Context checking to resolve identifiers

Behavior changed in R2021a

MATLAB uses additional context to resolve identifiers like variable names in an eval statement. As a result, MATLAB resolves ambiguities differently than in previous releases. Some code now produces errors or warnings.

Code that warns starting in R2021a will error in a future release.

Example	Previous Result	R2021 Result	Notes
function myfun(pi) eval('pi') end >> myfun	ans = 3.1416	Errors	MATLAB resolves pi as a variable in the function workspace, so myfun now errors when pi is not defined.
function myfun disp(pi) eval('pi = 1'); end >> myfun	3.1416 pi = 1	Same output but warns on assignment.	MATLAB resolves pi as a variable in the function workspace, even though it is a call to the function pi. In a future release, myfun errors, consistent with the processing of this function: function myfun disp(pi) pi = 1; end
% assignLocal.m script: local = 1; % myfun.m file with local function: function myfun local() assignLocal eval("local") end function local disp("local fx") end % function call: >> myfun	local fx local = 1	Same output but warns on assignment.	In a future release, MATLAB will give precedence as described in Function Precedence Order. In this example, precedence goes to the local function, consistent with the processing of this function: function myfun local() assignLocal local() end