exist - Check existence of variable, script, function, folder,

or class - MATLAB (original) (raw)

Check existence of variable, script, function, folder, or class

Syntax

Description

exist [name](#f5-453632-name) returns the type ofname as a number. This list describes the type associated with each value:

• 0 — name does not exist or cannot be found for other reasons. For example, if name exists in a restricted folder to which MATLAB® does not have access, exist returns 0.
• 1 — name is a variable in the workspace.
• 2 — name is a file with extension.m, .mlx, or.mlapp, or name is the name of a file with a non-registered file extension (.mat,.fig, .txt).
• 3 — name is a MEX-file on your MATLAB search path.
• 4 — name is a loaded Simulink® model or a Simulink model or library file on your MATLAB search path.
• 5 — name is a built-in MATLAB function. This does not include classes.
• 6 — name is a P-code file on your MATLAB search path.
• 7 — name is a folder.
• 8 — name is a class. (exist returns 0 for Java classes if you start MATLAB with the -nojvm option.)

MATLAB searches starting at the top of the search path, and moving down until a result is found or the last folder on the path is reached. If more than onename exists in a folder, MATLAB displays the first instance of name, according to the Function Precedence Order. Folders are an exception to the function precedence rules. They have precedence over all types except for variables and built-in functions.

For example, if name matches both a file with a .m extension and a P-code file, then exist returns 6, identifying it as a P-code file. If name matches both a variable and a P-code file, exists returns 1, identifying it as a variable. If name matches both a folder and a MATLAB function, exist returns 7, identifying it as a folder.

example

exist [name](#f5-453632-name) [searchType](#f5-453632-searchType) returns the type of name, restricting results to the specified type, searchType. If name of type searchType does not exist, MATLAB returns 0.

example

A = exist(___) returns the type of name to A.

example

Examples

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Check Existence of Workspace Variable

Create a variable named testresults, and then confirm its existence in the workspace.

testresults = magic(5); exist testresults

A variable named testresults exists in the workspace.

Check Existence of Folder

Create the folder myfolder, and then check its existence as a folder.

mkdir myfolder; exist myfolder dir

If you specify the type as file, MATLAB® searches for both files and folders, therefore returning the same result.

Check If MATLAB Function Is Built-In Function

Check whether the plot function is a built-in function or a file.

This indicates that plot is a built-in MATLAB function.

Input Arguments

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name — Name of variable, script, function, folder, or class

string scalar | character vector

Name of the variable, script, function, folder, or class, specified as a string scalar or character vector.

To specify name as a relative path, it must fit one of these descriptions:

• A folder on the search path
• In a folder on the search path
• The current folder
• In the current folder

Files and folders at a remote location, you must specify the full path as a uniform resource locator (URL). Internet URLs must include the protocol type "http://" or "https://". For more information, see Work with Remote Data.

Subfolders of folders on the path are not searched.

If name specifies a file with a non-registered file extension (.mat, .fig,.txt), include the extension. You can also include an extension to prevent a conflict with other similar filenames. For example,exist file.txt orexist("file.txt").

Note

MATLAB does not examine the contents or internal structure of a file and relies solely on the file extension for classification.

searchType — Type of results to search for

builtin | class | dir | file | var

Type of results to search for, specified as one of these values:

Limitations

• MATLAB does not support internet URLs that require authentication.
• MATLAB Online™ supports internet URLs associated with Microsoft® OneDrive™ files and folders, while the installed version of MATLAB supports only local OneDrive files.

Alternative Functionality

• To check the existence of a file or folder, you also can use the isfolder or isfile functions. exist searches for files and folders on the search path, which can lead to unexpected results. isfolder and isfile search for files or folders only on the specified path or in the current folder, which can lead to clearer and faster results.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• The input arguments must be string or character literals.
• You must provide the searchType input argument and only the "var", "file", and"dir" search types.
• When searching for a file or folder, the code generator treats theexist function as extrinsic. Therefore, the"file" and "dir" search types are not supported for standalone code generation. To check the existence of a file or folder in standalone code generation, use the isfolder and isfile functions.
• If you call exist by using a function handle, code generation does not support the "var" search type.
• Searching for a local variable in a function is supported only if this variable is defined on all or no execution paths.
• Searching for local variables is not supported inside loops, nested functions, or anonymous functions.
• Searching for varargout and repeating output arguments is not supported.
• In code generation, a global or persistent variable exists everywhere in the body of the function in which the variable is declared. By contrast, in MATLAB execution, a global or persistent variable exists only after it is declared in the function body.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced before R2006a

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R2024b: Read data over HTTP and HTTPS using file operation functions

You can read data from primary online sources by performing file read operations over an internet URL.

R2024b: C/C++ code generation support

You can generate code for exist function calls that search for variables, with some limitations. When searching for a file or folder, the code generator treats the exist function as extrinsic.