Add 'nix build' manpage

src/nix/build.cc

@@ -43,22 +43,11 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
         return "build a derivation or fetch a store path";
     }
 
-    Examples examples() override
+    std::string doc() override
     {
-        return {
-            Example{
-                "To build and run GNU Hello from NixOS 17.03:",
-                "nix build -f channel:nixos-17.03 hello; ./result/bin/hello"
-            },
-            Example{
-                "To build the build.x86_64-linux attribute from release.nix:",
-                "nix build -f release.nix build.x86_64-linux"
-            },
-            Example{
-                "To make a profile point at GNU Hello:",
-                "nix build --profile /tmp/profile nixpkgs#hello"
-            },
-        };
+        return
+          #include "build.md"
+          ;
     }
 
     void run(ref<Store> store) override

src/nix/build.md

@@ -0,0 +1,92 @@
+R""(
+
+# Examples
+
+* Build the default package from the flake in the current directory:
+
+  ```console
+  # nix build
+  ```
+
+* Build and run GNU Hello from the `nixpkgs` flake:
+
+  ```console
+  # nix build nixpkgs#hello
+  # ./result/bin/hello
+  Hello, world!
+  ```
+
+* Build GNU Hello and Cowsay, leaving two result symlinks:
+
+  ```console
+  # nix build nixpkgs#hello nixpkgs#cowsay
+  # ls -l result*
+  lrwxrwxrwx 1 … result -> /nix/store/v5sv61sszx301i0x6xysaqzla09nksnd-hello-2.10
+  lrwxrwxrwx 1 … result-1 -> /nix/store/rkfrm0z6x6jmi7d3gsmma4j53h15mg33-cowsay-3.03+dfsg2
+  ```
+
+* Build a specific output:
+
+  ```console
+  # nix build nixpkgs#glibc.dev
+  # ls -ld ./result-dev
+  lrwxrwxrwx 1 … ./result-dev -> /nix/store/dkm3gwl0xrx0wrw6zi5x3px3lpgjhlw4-glibc-2.32-dev
+  ```
+
+* Build attribute `build.x86_64-linux` from (non-flake) Nix expression
+  `release.nix`:
+
+  ```console
+  # nix build -f release.nix build.x86_64-linux
+  ```
+
+* Build a NixOS system configuration from a flake, and make a profile
+  point to the result:
+
+  ```console
+  # nix build --profile /nix/var/nix/profiles/system \
+      ~/my-configurations#nixosConfigurations.machine.config.system.build.toplevel
+  ```
+
+  (This is essentially what `nixos-rebuild` does.)
+
+* Build an expression specified on the command line:
+
+  ```console
+  # nix build --impure --expr \
+      'with import <nixpkgs> {};
+       runCommand "foo" {
+         buildInputs = [ hello ];
+       }
+       "hello > $out"'
+  # cat ./result
+  Hello, world!
+  ```
+
+  Note that `--impure` is needed because we're using `<nixpkgs>`,
+  which relies on the `$NIX_PATH` environment variable.
+
+* Fetch a store path from the configured substituters, if it doesn't
+  already exist:
+
+  ```console
+  # nix build /nix/store/rkfrm0z6x6jmi7d3gsmma4j53h15mg33-cowsay-3.03+dfsg2
+  ```
+
+# Description
+
+`nix build` builds the specified *installables*. Installables that
+resolve to derivations are built (or substituted if possible). Store
+path installables are substituted.
+
+Unless `--no-link` is specified, after a successful build, it creates
+symlinks to the store paths of the installables. These symlinks have
+the prefix `./result` by default; this can be overriden using the
+`--out-link` option. Each symlink has a suffix `-<N>-<outname>`, where
+*N* is the index of the installable (with the left-most installable
+having index 0), and *outname* is the symbolic derivation output name
+(e.g. `bin`, `dev` or `lib`). `-<N>` is omitted if *N* = 0, and
+`-<outname>` is omitted if *outname* = `out` (denoting the default
+output).
+
+)""