Linux – Where is the PHP executable on Ubuntu

In general the /proc filesystem works in a similar way, I think. Follow The Linux Kernel Module Programming Guide.

Or create your own FUSE which will work in user space.

Edit
There is a FUSE that seems to do just that: ScriptFS. Its README says:

ScriptFS is a new file system which merely replicates a local file system, but replaces all files detected as "scripts" by the result of their execution.

Any script is supported. In a usual way of working, ScriptFS reads on its command line the name of two programs : one that is the script interpretor, and the other one a lightweight program that tells fast if a file on the disk is a script that can be read by the first program.

I guess if you build these two programs right, they will be able to use shebangs.

Note: I have never used ScriptFS (yet).

Your $PATH includes ~/.local/bin where tilde hasn't been expanded. bash will expand it on the fly each time, but which (at least on Ubuntu) or sh won't.

If you want which to see the executables in ~/.local/bin you need to make sure tilde is expanded before the PATH variable gets it. The string ~/.local/bin is probably added to your PATH by one of the startup scripts. Find the relevant line and fix it according to the examples below.

_{Note: first run each of the following examples in a fresh shell, so you can observe (echo "$PATH") how it changes the variable each time independently.}

This won't expand tilde character (because of quoting):

PATH="~/.local/bin:$PATH"

This will:

PATH=~/".local/bin:$PATH"

Or this:

PATH=~/.local/bin:$PATH

Rules of tilde expansion are somewhat complicated. Consider using $HOME. Examples:

PATH="$HOME/.local/bin:$PATH"
PATH="$PATH:$HOME/.local/bin"

To fix an already established PATH variable, replace ~ in it with the content of $HOME:

PATH="${PATH/\~/$HOME}"