How to Use the -wait Flag in MATLAB for Command-Line Execution

If you’ve ever tried running a MATLAB script from the command line, you may have encountered a situation where MATLAB starts executing your script but returns control to the command line immediately. This can be confusing and inconvenient if you’re expecting MATLAB to finish processing before continuing with other commands.

Many users have asked: How can I stop MATLAB from returning until after a command-line script completes? In this blog post, we’ll explore how to enforce this behavior using the command line, specifically through the -wait flag.

The Issue at Hand

Typically, when you run a MATLAB file using the command line, you might use a command like this:

matlab -nosplash -nodesktop -r waitHello

Even though the script called waitHello runs correctly, control returns to the command line immediately after initiating the command. This behavior is undesirable if you need to ensure that your script completes before proceeding further in your workflow.

Example Script

To illustrate this issue, consider the following simple MATLAB function stored in a file named waitHello.m:

function waitHello
    disp('Waiting...');
    pause(3); % pauses for 3 seconds
    disp('Hello World');
    quit;
end

When executed, the script will display a message, pause for three seconds, and then display “Hello World.” However, if you run it using the standard command line call, the command line will return control immediately while the script is still executing.

The Solution: Using the -wait Flag

To ensure MATLAB waits for your script to complete execution before returning control to your command line, you can use the -wait option in your command. The modified command would look like this:

matlab -wait -nosplash -nodesktop -r waitHello

Explanation of the Command

  • -wait: This is the critical option that instructs MATLAB to wait for the script to finish. It is an undocumented feature in older versions (like MATLAB 7.1), but it can serve your purpose well.
  • -nosplash: This flag prevents the MATLAB splash screen from appearing.
  • -nodesktop: This option allows you to run MATLAB without the desktop environment, which can be useful for running scripts in a server or console mode.
  • -r waitHello: This flag tells MATLAB to run the waitHello function.

Important Considerations

  • Ensure that your script ends by calling quit to prevent MATLAB from hanging, waiting for user input.
  • If you encounter any issues with the -wait flag not working as intended, check the documentation for your specific version of MATLAB to verify support for this flag.

Conclusion

By incorporating the -wait flag into your MATLAB command line execution, you can effectively keep MATLAB from returning control until your script has completed running. This improvement streamlines your workflow and ensures that your scripts can run to completion without confusion.

Feel free to reach out or comment if you have any further questions or if you wish to share your experiences with MATLAB command-line scripting!