Low-level derivations: Difference between revisions

@@ Line 12: / Line 12: @@
    name = "hello-world";
    system = builtins.currentSystem;
-   builder = "/bin/sh";
+   builder = "/bin/bash";
    args = [
-     "-c"
+    "-c"
-     "echo 'Hello, World!' </nowiki>><nowiki> $out"
+     "echo '#!/bin/bash' </nowiki>><nowiki> $out"
+    "echo 'echo \"Hello, World!\"' </nowiki>><nowiki> $out"
+    "chmod +x $out"
    ];
-}</nowiki>}}
+}</nowiki>}}There are a number of elements in this Nix file, but remembering the conceptual model of a framework makes quick work of figuring them out: a derivation is a set of ''inputs along with an executable'' that produces a deterministic ''output'', following a list of ''steps.'' Here our inputs are quite literally the key-value pairs in the derivation [[Attribute set|attrset]]: the <code>name</code> of the derivation and the system it's being built ''for''. The executable (called the builder) is the program found at <code>/bin/bash</code>. And the steps are:
+# Write the string <code>#!/bin/bash</code> to the output file (<code>$out</code>);
+# Write the string <code>echo "Hello, World!"</code> to the output file;
+# Make the output file executable.