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| author | Guillaume Maudoux <guillaume.maudoux@tweag.io> | 2022-09-07 00:34:03 +0200 |
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| committer | Guillaume Maudoux <guillaume.maudoux@tweag.io> | 2022-09-07 00:34:03 +0200 |
| commit | eb460a9529dd79995b6b788d59322fbc8f989214 (patch) | |
| tree | 2dec54ef6b3096d787cb49cb0f2f6b7041b1f6c1 /doc/manual/src/language/builtin-constants.md | |
| parent | 9ff892aad4ee13532ea84cb6e4a2a53d70945efe (diff) | |
| parent | 96001098796c9011d1670cc8a7acd00ef49b2d7a (diff) | |
WIP: broken merge but need a git checkpoint
Diffstat (limited to 'doc/manual/src/language/builtin-constants.md')
| -rw-r--r-- | doc/manual/src/language/builtin-constants.md | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/doc/manual/src/language/builtin-constants.md b/doc/manual/src/language/builtin-constants.md new file mode 100644 index 000000000..78d066a82 --- /dev/null +++ b/doc/manual/src/language/builtin-constants.md @@ -0,0 +1,20 @@ +# Built-in Constants + +Here are the constants built into the Nix expression evaluator: + + - `builtins`\ + The set `builtins` contains all the built-in functions and values. + You can use `builtins` to test for the availability of features in + the Nix installation, e.g., + + ```nix + if builtins ? getEnv then builtins.getEnv "PATH" else "" + ``` + + This allows a Nix expression to fall back gracefully on older Nix + installations that don’t have the desired built-in function. + + - [`builtins.currentSystem`]{#builtins-currentSystem}\ + The built-in value `currentSystem` evaluates to the Nix platform + identifier for the Nix installation on which the expression is being + evaluated, such as `"i686-linux"` or `"x86_64-darwin"`. |