mkdir — Create folders in MATLAB and RunMat.

mkdir creates folders on disk using single-path or parent/child path forms. Status/message outputs and filesystem error behavior follow MATLAB semantics.

Syntax

status = mkdir(folderName)
status = mkdir(parentFolder, folderName)
[status, msg, msgID] = mkdir(folderName)
[status, msg, msgID] = mkdir(parentFolder, folderName)

Inputs

Returns

Returned values from mkdir depend on how many outputs the caller requests.

Errors

How mkdir works

• status = mkdir(folder) creates folder, returning 1 when the directory is created or already exists, and 0 on failure. Status outputs are double scalars for MATLAB compatibility.
• [status, message, messageID] = mkdir(parent, child) creates the directory fullfile(parent, child). When the directory is created during this call, the message outputs are empty. If the directory already exists, MATLAB populates them with 'Directory already exists.' and 'RunMat:MKDIR:DirectoryExists'. Failures return the system error text and message identifier.
• The optional message and messageID outputs are character arrays (with size 1×0 when empty), matching MATLAB’s behaviour. Callers that prefer string scalars can wrap them with string(message).
• Passing a parent folder that does not exist leaves the filesystem unchanged and returns status = 0.
• If the target path already exists as a file, mkdir fails gracefully with status = 0 and a diagnostic message; it does not overwrite files.
• Path arguments accept character vectors or string scalars. Other input types raise mkdir: folder name must be a character vector or string scalar (or the equivalent message for the parent argument).
• The builtin expands ~ to the user’s home directory and honours relative paths with respect to the current working folder (pwd).

Does RunMat run mkdir on the GPU?

mkdir performs host-side filesystem operations. When callers supply GPU-resident scalars (for example, gpuArray("logs")), RunMat gathers the value back to the CPU before resolving the path. Acceleration providers do not publish hooks for this builtin, so there is no device-side implementation to enable.

GPU memory and residency

No. mkdir executes entirely on the host—GPU residency provides no benefit. However, if a script accidentally stores path strings on the GPU, RunMat automatically gathers them before accessing the filesystem so the call still succeeds.

Examples

Create A New Folder In The Current Directory

status = mkdir("results")

Expected output:

status =
     1

Create A Nested Folder Using Parent And Child Arguments

mkdir("data");
status = mkdir("data", "archive/2024")

Expected output:

status =
     1

Detect When A Folder Already Exists

mkdir("logs");
[status, message, messageID] = mkdir("logs")

Expected output:

status =
     1

message =
Directory already exists.

messageID =
RunMat:MKDIR:DirectoryExists

Handle Missing Parent Folder Gracefully

[status, message, messageID] = mkdir("missing-parent", "child")

Expected output:

status =
     0
message =
Parent folder "missing-parent" does not exist.
messageID =
RunMat:MKDIR:ParentDirectoryDoesNotExist

Capture Detailed Status And Messages

[status, message, messageID] = mkdir("reports")

Expected output:

status =
     1
message =

messageID =

Create A Folder In Your Home Directory With Tilde Expansion

status = mkdir("~", "RunMatProjects")

Expected output:

status =
     1

Use gpuArray Inputs For Paths

status = mkdir(gpuArray("gpu-output"))

Expected output:

status =
     1

Using mkdir with coding agents

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

FAQ

Related Io functions

Open-source implementation

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

• View the source for mkdir 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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