strrep — Replace non-overlapping substring occurrences in text inputs with MATLAB-compatible container behavior.

strrep(str, old, new) replaces every non-overlapping occurrence of old with new. It supports MATLAB-compatible string, char, and cellstr-style inputs with element-wise replacement semantics.

Syntax

newStr = strrep(str, old, new)

Inputs

Returns

Errors

How strrep works

• String scalars remain strings. Missing string values (<missing>) propagate unchanged.
• String arrays are processed element-wise while preserving their full shape and orientation.
• Character arrays are handled row by row. Rows expand or shrink as needed and are padded with spaces so the result stays a rectangular char array, just like MATLAB.
• Cell arrays must contain character vectors or string scalars. The result is a cell array of identical size where each element has had the replacement applied.
• The old and new arguments must be string scalars or character vectors of the same data type.
• old can be empty. In that case, strrep inserts new before the first character, between existing characters, and after the final character.

Does RunMat run strrep on the GPU?

RunMat treats text replacement as a CPU-first workflow:

1. The builtin is registered as an Accelerate *sink*, so the planner gathers any GPU-resident inputs (string arrays, char arrays, or cell contents) back to host memory before work begins. 2. Replacements are computed entirely on the CPU, mirroring MATLAB’s behaviour and avoiding GPU/device divergence in string handling. 3. Results are returned as host values (string array, char array, or cell array). Residency is never pushed back to the GPU, keeping semantics deterministic regardless of the active provider.

GPU memory and residency

No. strrep registers as a sink with RunMat Accelerate, so the fusion planner never keeps its inputs or outputs on the GPU. Even if you start with GPU data, the runtime gathers it automatically—manual gpuArray or gather calls are unnecessary.

Examples

Replacing a word inside a string scalar

txt = "RunMat turbo mode";
result = strrep(txt, "turbo", "accelerate")

Expected output:

result = "RunMat accelerate mode"

Updating every element of a string array

labels = ["GPU planner", "CPU planner"];
updated = strrep(labels, "planner", "pipeline")

Expected output:

updated = 2×1 string
    "GPU pipeline"
    "CPU pipeline"

Preserving rectangular shape in character arrays

chars = char("alpha", "beta ");
out = strrep(chars, "a", "A")

Expected output:

out =

  2×5 char array

    'AlphA'
    'betA '

Applying replacements inside a cell array of character vectors

C = {'Kernel Fusion', 'GPU Planner'};
renamed = strrep(C, ' ', '_')

Expected output:

renamed = 1×2 cell array
    {'Kernel_Fusion'}    {'GPU_Planner'}

Inserting text with an empty search pattern

stub = "abc";
expanded = strrep(stub, "", "-")

Expected output:

expanded = "-a-b-c-"

Leaving missing string values untouched

vals = ["RunMat", "<missing>", "Accelerate"];
out = strrep(vals, "RunMat", "RUNMAT")

Expected output:

out = 1×3 string
    "RUNMAT"    <missing>    "Accelerate"

Replacing substrings gathered from GPU inputs

g = gpuArray("Turbine");
host = strrep(g, "bine", "bo")

Expected output:

host = "Turbo"

Using strrep with coding agents

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

FAQ

Related Strings functions

Open-source implementation

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

• View the source for strrep 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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