fgetl — Read the next line without newline characters in MATLAB and RunMat.

fgetl(fid) reads the next line from a text file and removes trailing line terminators from the returned character row vector. End-of-file signaling and file-position behavior follow MATLAB semantics, so empty lines remain distinguishable from EOF.

Syntax

tline = fgetl(fid)

Inputs

Returns

Errors

How fgetl works

• tline = fgetl(fid) reads from the current file position to the next line terminator or to end-of-file when no terminator is found.
• Line terminators are consumed but not included in the returned character row vector. RunMat recognises \n, \r\n, and \r.
• When the file is empty or the file position indicator is already at end-of-file, fgetl returns the numeric sentinel -1.
• An empty line returns an empty character row vector, not -1.
• Lines are decoded using the text encoding recorded by fopen. UTF-8, US-ASCII, ISO-8859-1 (latin1), Windows-1252, Shift_JIS, and binary mode are recognised without additional user work.

Does RunMat run fgetl on the GPU?

fgetl is a host-only operation. File identifiers live in the host registry created by fopen, so GPU-resident scalar arguments are gathered back to the CPU before the read occurs.

Examples

Read the first line of a file without the newline

% Browser sandbox: you must be logged in
% to save files for this example.
fname = tempname;
fid = fopen(fname, 'w');
fprintf(fid, 'RunMat\nSecond line\n');
fclose(fid);

fid = fopen(fname, 'r');
line = fgetl(fid);
fclose(fid);
delete(fname);

line

Expected output:

line =
    'RunMat'

Read a file line by line

% Browser sandbox: you must be logged in
% to save files for this example.
fname = tempname;
fid = fopen(fname, 'w');
fprintf(fid, 'one\n');
fprintf(fid, 'two\n');
fclose(fid);

fid = fopen(fname, 'r');
tline = fgetl(fid);
while tline ~= -1
    disp(tline);
    tline = fgetl(fid);
end
fclose(fid);
delete(fname)

Expected output:

one
two

Distinguish an empty line from end of file

% Browser sandbox: you must be logged in
% to save files for this example.
fname = tempname;
fid = fopen(fname, 'w');
fprintf(fid, '\nlast');
fclose(fid);

fid = fopen(fname, 'r');
line1 = fgetl(fid);
line2 = fgetl(fid);
line3 = fgetl(fid);
fclose(fid);
delete(fname);

isempty(line1)
line2
line3

Expected output:

ans =
  logical
   1
line2 =
    'last'
line3 =
    -1

Read a final line without a trailing newline

% Browser sandbox: you must be logged in
% to save files for this example.
fname = tempname;
fid = fopen(fname, 'w');
fprintf(fid, 'last line');
fclose(fid);

fid = fopen(fname, 'r');
line1 = fgetl(fid);
line2 = fgetl(fid);
fclose(fid);
delete(fname);

line1
line2

Expected output:

line1 =
    'last line'
line2 =
    -1

Using fgetl with coding agents

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

FAQ

Related Io functions

Open-source implementation

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

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

About RunMat

RunMat is an open-source runtime that executes MATLAB-syntax code blazing on any GPU. It is licensed under the Apache 2.0 license.

• RunMat automatically optimizes your math for GPU execution on Apple, Nvidia, and AMD hardware. No code changes needed. Simulations that took hours now take minutes.
• Start running code in seconds. RunMat runs in the browser, on the desktop, or from the CLI. No license server, no IT ticket.

Getting started · Benchmarks · Pricing