Redirect input from code or terminal to running code or terminal?

Question

Currently, I am using a software script that requires continuous input through the terminal. The script evaluates files continuously by receiving path input and evaluating the file in the path.

The goal: Is it possible to run a script requiring input through passing input from another terminal or script.

The evaluation software loads a lot of data before being ready for processing, that is why I would prefer to keep the software running and simply pass input from time to time. Instead of starting up the software and load all data required (which takes time).

I can mention that I have tried tty to find:
$ /dev/pts/19
then through other terminal run: $ <command> <myinput> > /dev/pts/19
where command is replaced with 'echo / print'
However, it just prints in the other terminal, it does not act as input to the software.

Answer 1

Create a named pipe:

mkfifo pipe

Make sure it won't close (see this answer):

exec 3<>pipe

Feed your script from the pipe:

<pipe your_script.sh
# or if you want to see incoming data
<pipe tee >(your_script.sh)

Then from another terminal use echo, printf or whatever:

echo "/some/path/or/another/input" > pipe

or

cat large_input.txt > pipe

or

script_that_generates_input.sh > pipe

But beware of race condition! Don't feed the pipe from two or more sources at the same time; always wait for the current feeding command to exit before you run the next. Note if one source passes a lot of data, it may be held midway, until the receiving side processes the data. Put mbuffer (with arguments that fit your usage case) before your_script.sh to create a buffer that can store more incoming data before any feeding command is put on hold.