I have a long-running Matlab script for data processing. I want to send it a flag over stdin to tell it I have new data to process. I also want to read a flag from stdout when it is done processing.
In other words, I have a Process A that sends a flag about once a minute to Matlab. I want Matlab to wait until it receives this flag.
Writing to stdout in a matlab process is as easy as calling fprintf. But how can I read from stdin? Documentation on fopen doesn't mention an input pipe, and neither does fread. How can get a Matlab script to read from stdin?
It actually turns out that the solution is as simple as input. Write the following into myscript.m:
str = input('', 's');
fprintf(str);
exit;
Then, run the following in a shell:
echo Hello world | matlab -nosplash -nodisplay -nodesktop -r "myscript"
Indeed, we see that "Hello world" is printed to the console, along with Matlab's startup text.
So, in summary, input reads from stdin, and fprintf writes to stdout.
One way to do this is using a named pipe. In a shell, run mkfifo MY_PIPE to make a named pipe. This will make a file-like object called MY_PIPE that you can read and write to. Then, redirect the output of the program sending data to MY_PIPE, e.g. ./program.sh > MY_PIPE. Finally, to read from the pipe in Matlab, you can use fopen('MY_PIPE', 'r').
Note that answer is limited in a few ways:
It will only run in a Linux environment and with access to the shell.
It doesn't make use of Matlab built-ins and is kind of hackish.
