Remote: deps: use `directory`

[Anton-Latukha]

which depends on TH & shelly which depends on a lot of things and also directory.

Tangent: it is useful to know that which is a clone of command -v which seems like always was in POSIX: "The early Unix shells until the late 70s had ... only the traditional looking up of executables in $PATH" (which is command -v), Bourne shell (sh) had it also, seems like always. The which is a script from "3BSD (1980)" that introduced this functionality into csh, it stuck because of popularity of csh and the name being mnemonic. command -v works even in fish, though, not being documented in it (... oh, now is). Long story short - command -v is a shell builtin.

That is why declaring the requirement of pkgs.which in the Nix derivation overlay triggered my attention. If there is sh present - the which executable is not needed. Or for programming languages - if in OS where there is at least POSIX.1 (1988) support (which now again includes Microsoft Windows, not mentioning others, so we can claim POSIX.1 supported "always"), the replacement of basic which use is 1 call to system function.

---

POSIX API has a function named system:

NAME

    system - issue a command

SYNOPSIS

    #include <stdlib.h>

    int system(const char *command);

DESCRIPTION

    The system() function shall behave as if a child process were created using fork(), and the child process invoked the sh utility using execl() as follows:

    execl(<shell path>, "sh", "-c", command, (char *)0);

So the system function and sh features are isomorphic and central to the POSIX and most OSes, and so their use in programming languages is trivial. system allows to run in the env any commands, so even the command -v which can run without the need of locating the shell (system(command)).

Knowing these 2 things allows understanding what can be done with direct use of POSIX calls, what sh can do - in Haskell also "should be" one-several POSIX calls away.