`exist` — Determine whether variables, files, folders, or symbols exist in MATLAB and RunMat.

exist(name) returns an integer code identifying whether a named variable, file, folder, builtin, class, or related symbol is available. Optional type filters and return-code behavior follow MATLAB and RunMat lookup semantics.

Syntax

code = exist(name)
code = exist(name, type)

Inputs

Name	Type	Required	Default	Description
`name`	`Any`	Yes	—	Variable/function/file/class name to query.
`type`	`StringScalar`	Yes	—	Query kind: var\|file\|dir\|builtin\|class\|handle\|method\|mex\|pcode\|simulink\|thunk\|lib\|java.

Returns

Name	Type	Description
`code`	`NumericScalar`	Existence code (0,1,2,3,4,5,6,7,8) following MATLAB semantics.

Errors

Identifier	When	Message
—	More than two total input arguments are provided.	`exist: too many input arguments`
—	Name input is not a character vector or string scalar/array scalar.	`exist: name must be a character vector or string scalar`
—	Type input is not a character vector or string scalar/array scalar.	`exist: type must be a character vector or string scalar`
—	Type input is not one of the supported exist query types.	`exist: invalid type. Type must be one of 'var', 'variable', 'file', 'dir', 'directory', 'folder', 'builtin', 'built-in', 'class', 'handle', 'method', 'mex', 'pcode', 'simulink', 'thunk', 'lib', 'library', or 'java'`

How `exist` works

Searches follow MATLAB's precedence: variables first, then built-ins, classes, compiled code (MEX/P-code), standard files, and finally folders.
When you omit the type, exist returns the first match respecting this precedence.
String handling matches MATLAB: name and the optional type must be character vectors or string scalars. String arrays must contain exactly one element.
Paths expand ~ to the user's home folder. Relative paths resolve against the current working directory, and RunMat honours RUNMAT_PATH / MATLABPATH entries when searching for scripts and classes.
Package-qualified names such as pkg.func and pkg.Class map to +pkg folders automatically. Class queries also recognise @ClassName folders and .m files that contain classdef.
GPU-resident arguments (for example, gpuArray("script")) are gathered automatically, so callers never need to move text back to the CPU manually.
Unsupported second-argument types surface a MATLAB-compatible error listing the accepted keywords.

Does RunMat run `exist` on the GPU?

The builtin runs entirely on the host CPU. If any argument lives on the GPU, RunMat gathers it to host memory before performing the lookup. Providers do not implement dedicated hooks for exist, and the result is always returned as a host-resident double scalar. Documented behaviour is identical regardless of whether acceleration is enabled.

GPU memory and residency

No. exist gathers any GPU-resident string inputs transparently. The lookup, file system checks, and return value are always host-side operations. Keeping text on the GPU offers no performance benefits, so you can pass regular character vectors or string scalars.

Examples

How to check if a workspace variable exists

alpha = 3.14;
status = exist("alpha", "var")

Expected output:

status =
     1

How to determine if a built-in function is available

code = exist("sin")

Expected output:

code =
     5

How to test whether an M-file is on the MATLAB path

status = exist("utilities/process_data", "file")

Expected output:

status =
     2

How to verify a folder exists before creating logs

mkdir("logs");
status = exist("logs", "dir")

Expected output:

status =
     7

How to detect class definitions in packages

status = exist("pkg.Widget", "class")

Expected output:

status =
     8

How to inspect compiled MEX fallbacks

if exist("fastfft", "mex")
    disp("Using compiled fastfft.");
else
    disp("Falling back to MATLAB implementation.");
end

Expected output:

% Prints which implementation will be executed based on the presence of fastfft.mex*.

Using `exist` with coding agents

Open a RunMat example with live inputs, then ask the agent to explain how exist changes the result.

Run a small exist example, explain the result, then change one input and compare the output.

FAQ

Does exist support wildcards?⌄

No. Strings containing * or ? return 0, matching MATLAB behaviour.

What about Simulink models or Java classes?⌄

RunMat reports 4 for .slx / .mdl files. Java class detection is not implemented yet and currently returns 0, mirroring MATLAB when Java support is unavailable.

How are packages handled?⌄

Names like pkg.func translate to +pkg/func.m. Class queries additionally search +pkg/@Class folders.

Is the search path configurable?⌄

Yes. RunMat honours the current working directory plus any folders listed in RUNMAT_PATH or MATLABPATH (path separator aware).

What's the search precedence when multiple items share a name?⌄

Variables have highest priority, followed by built-ins, classes, compiled code (MEX/P-code), standard files, and folders last—exactly like MATLAB.

What happens with unsupported type keywords?⌄

The builtin raises exist: invalid type... describing the accepted tokens, matching MATLAB's diagnostic.

Do handle queries work?⌄

When the first argument is a RunMat handle object, exist(handle, "handle") returns 1. Numeric graphics handles are not yet supported and return 0.

What does exist do in MATLAB?⌄

exist(name, type) checks whether a variable, file, folder, or function named name exists and returns a numeric code indicating what kind of item was found. Zero means nothing was found.

How do I check if a file exists in MATLAB?⌄

Use exist('filename.m', 'file'). It returns 2 if the file is found on the MATLAB path, or 0 if not found. In RunMat, the same syntax works.

What are the return codes for exist in MATLAB?⌄

exist returns 0 (not found), 1 (variable in workspace), 2 (file on path), 3 (MEX file), 4 (Simulink model), 5 (built-in function), 7 (folder), or 8 (Java class). RunMat supports codes 0, 1, 2, 5, and 7.

What does each exist return value mean?⌄

— The complete MATLAB table is:

| Code | Meaning | |------|---------| | 0 | Not found | | 1 | Variable in the active workspace | | 2 | File (including .m scripts, .mat, and most data files on the path) | | 3 | MEX-file (compiled C/C++/Fortran) | | 4 | Simulink model (.slx / .mdl) | | 5 | Built-in function | | 6 | P-code file (.p) | | 7 | Folder | | 8 | Class (classdef or @Class folder) |

Use the two-argument form (exist(name, 'file'), exist(name, 'dir'), exist(name, 'builtin'), exist(name, 'class')) when you want to restrict the search to a single kind.

How do I check if a variable or file exists before using it?⌄

— Use the two-argument form so the result is unambiguous:

if exist('myVar', 'var')
    disp(myVar);
end

if exist('data.mat', 'file')
    load('data.mat');
end

For files specifically, isfile('data.mat') and isfolder('outdir') return plain logicals and are often clearer than exist alone.

How do I create a folder only if it doesn't already exist?⌄

— Combine exist with mkdir:

if ~exist('outdir', 'dir')
    mkdir('outdir');
end

A newer, equally idiomatic alternative is if ~isfolder('outdir'), mkdir('outdir'); end. mkdir itself is a no-op when the folder already exists (it just prints a warning), so either pattern is safe.

Open-source implementation

Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how exist is executed, line by line, in Rust.

View the source for exist in Rust on GitHub
Learn how the RunMat runtime works
Found a bug? Open an issue with a minimal reproduction.

About RunMat

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exist — Determine whether variables, files, folders, or symbols exist in MATLAB and RunMat.

Syntax

Inputs

Returns

Errors

How exist works

Does RunMat run exist on the GPU?

GPU memory and residency

Examples

How to check if a workspace variable exists

How to determine if a built-in function is available

How to test whether an M-file is on the MATLAB path

How to verify a folder exists before creating logs

How to detect class definitions in packages

How to inspect compiled MEX fallbacks

Using exist with coding agents

FAQ

Related Io functions

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Mat

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Open-source implementation

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`exist` — Determine whether variables, files, folders, or symbols exist in MATLAB and RunMat.

How `exist` works

Does RunMat run `exist` on the GPU?

Using `exist` with coding agents