How can I determine on my system where process substitution creates FIFO files?

Question

I'm writing a C++ application and need to work with process substitution in the Bash shell.

I'm trying to find a way to validate the paths passed as arguments to my program, some of which point to FIFO files created by process substitution.

Is there a shell (or C++) way that I can check if the system creates these files in /dev/fd or if they are created somewhere else?

Answer 1

The short answer is that you cannot do this. Just because a directory is where bash defaults to putting fifo paths, doesn't mean that a particular fifo in that directory was created by bash, or that it was passed by bash as an argument to your command.

Take a look at the bigger picture of your problem. What are you REALLY trying to solve?

If you're trying to solve, "the output of my program must always be piped into another program," then don't require the user to use bash's obscure process substitution. What if the default shell on their system is zsh? Bourne shell? Korn shell?

Instead, have your program create a pipe, fork, and exec the other program.

So, what are you really trying to do? What happens if you, God forbid, write your output to a file the user of your program passed, instead of to a fifo created by bash?

Answer 2

Use the -p option to test if a file is a pipe:

#!/bin/bash
file="$1"
if [ -p "$file" ]
then
    echo "$file is a pipe"
fi

Demo:

$ myscript.sh <(echo hello)
/dev/fd/63 is a pipe