Provide arguments (via bash script) to a process that is already running

Question

I'm trying to have a bash script that does the following (in pseudocode):

#!/bin/bash
run myapp (which needs arguments given from stdin)
/* do some extra stuff */
provide arguments to hanging process myapp

For example, say you run myapp, and after it runs it asks for your name. I.e., I run it via bash, but I don't want to give it a name just yet. I just want it to run for now, while in the meantime bash does some other stuff, and then I want to provide my name (still via bash). How do I do this?

Answer 1

You can use an anonymous pipe:

# open a new file descriptor (3) and provide as stdin to myapp
exec 3> >(run myapp) 

# do some stuff ....

# write arguments to the pipe
echo "arg1 arg2 -arg3 ..." >&3

The advantage over a named pipe is the fact that you don't need to worry about cleaning up and you won't need any write permissions.

Answer 2

You can used a named pipe:

# create the named pipe
mkfifo fifo

# provide the named pipe as stdin to myapp
./myapp < fifo

# do something else
# ...

# write the arguments to the named pipe
./write_args_in_some_way > fifo

# remove the named pipe
rm fifo

You can also used an anonymous pipe, as indicated in the answer by @hek2mgl, which is probably better in this case. There are, however, a few advantages (which may not apply in this case) of named pipes vs anonymous pipes, as explained in this Stackexchange question.