58 lines
1.6 KiB
Prolog
58 lines
1.6 KiB
Prolog
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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Predicates for reasoning about the operating system (OS) environment.
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Written July 2020 by Markus Triska (triska@metalevel.at).
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Lists of characters are used throughout to represent keys and values.
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Example:
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?- getenv("LANG", Ls).
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Ls = "en_US.UTF-8".
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Public domain code.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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:- module(os, [getenv/2,
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setenv/2,
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unsetenv/1]).
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:- use_module(library(error)).
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:- use_module(library(charsio)).
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:- use_module(library(lists)).
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getenv(Key, Value) :-
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must_be_env_var(Key),
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'$getenv'(Key, Value).
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setenv(Key, Value) :-
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must_be_env_var(Key),
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must_be_chars(Value),
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'$setenv'(Key, Value).
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unsetenv(Key) :-
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must_be_env_var(Key),
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'$unsetenv'(Key).
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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For now, we only support a restricted subset of variable names.
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The reason is that Rust may panic if a key is empty, contains an
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ASCII equals sign '=' or the NUL character '\0', or when the value
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contains the NUL character.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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must_be_env_var(Cs) :-
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must_be_chars(Cs),
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Cs = [_|_],
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( maplist(permitted, Cs) -> true
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; domain_error(env_var, Cs, os)
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).
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permitted(C) :- char_type(C, alnum).
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permitted(C) :- char_type(C, ascii_punctuation).
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permitted('_').
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must_be_chars(Cs) :-
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must_be(list, Cs),
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maplist(must_be(character), Cs).
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