Opening a file in the user's home directory

Question

I've run into a strange problem using Core.In_channel library. Here's a piece of code meant to open a file in the user's home directory

open Core.Std
In_channel.with_file "~/.todo_list" ~f:(fun in_c ->
  (* Do something here... *)
)

However, when running this, here is what I get:

Exception: (Sys_error "~/.todo_list: No such file or directory").

I am absolutely sure that ~/.todo_list exists, but I suspect that the filename is misinterpreted by OCaml.

What am I missing here?

Answer 1

As others have said, the expansion of ~ is done by the shell, not by the underlying system. No shell is involved in your call to with_file so the string is interpreted literally as a file name.

If the code is running on behalf of a user who has logged in, the home directory is available as the value of the environment variable HOME.

# Unix.getenv "HOME";;
- : string = "/Users/username"

Otherwise you will need to extract the home directory from the user database.

# let open Unix in (getpwnam "username").pw_dir;;
- : string = "/Users/username"