Improve docs of nixops eval

nixops/__main__.py

@@ -528,14 +528,20 @@
 )
 
 subparser = add_subparser(
-    subparsers, "eval", help="eval the given file is nix code in the network expression"
+    subparsers,
+    "eval",
+    help="evaluate a Nix expression with the NixOps network as arguments",
 )
 subparser.set_defaults(op=op_eval)
-subparser.add_argument("code", metavar="CODE", help="code")
+subparser.add_argument("file", metavar="FILE", help="file containing a Nix expression")
 subparser.add_argument(
-    "--json", action="store_true", help="print the option value in JSON format"
+    "--json", action="store_true", help="convert and print the return value as JSON"
+)
+subparser.add_argument(
+    "--strict",
+    action="store_true",
+    help="enable strict evaluation, (use with --json if value is more than a level deep)",
 )
-subparser.add_argument("--strict", action="store_true", help="enable strict evaluation")
 
 subparser = add_subparser(
     subparsers,

nixops/deployment.py

@@ -503,7 +503,7 @@ def evaluate(self) -> None:
                 )
                 self.definitions[name] = defn
 
-    def evaluate_code(self, code: str, json: bool = False, strict: bool = False) -> str:
+    def evaluate_code(self, file: str, json: bool = False, strict: bool = False) -> str:
         """Evaluate nix code in the deployment specification."""
 
         exprs = self.nix_exprs
@@ -524,7 +524,7 @@ def evaluate_code(self, code: str, json: bool = False, strict: bool = False) ->
                     "false",
                     "--arg",
                     "evalFile",
-                    code,
+                    file,
                 ]
                 + (["--strict"] if strict else [])
                 + (["--json"] if json else []),

nixops/script_defs.py

@@ -897,7 +897,7 @@ def op_eval(args):
     with deployment(args) as depl:
         depl.evaluate()
         sys.stdout.write(
-            depl.evaluate_code(args.code, json=args.json, strict=args.strict)
+            depl.evaluate_code(args.file, json=args.json, strict=args.strict)
         )