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+# Nucleus Command Line Interface
+
+This is the spec for the minimum CLI options that nucleus implementations should expose.
+
+Implementations may also expose platform, vm, and other special options not found in the other implementations in addition to these.
+
+## nucleus [options] <file or dir> [--] ...
+
+Execute nucleus with the provided options on the specified app bundle and provide it with arguments if specified.
+
+The app bundle may be either a directory, a Zip file, or a JS file.
+
+The following rules apply depending on what is provided:
+
+##### Directory
+
+The directory will be considered the app bundle and nucleus will attempt to execute the default `main.js` file.
+
+##### Zip file
+
+The contents of the zip file will be considered the app bundle and nucleus will attempt to execute the default main.js file within it.
+
+##### JS file
+
+The file's parent directory will be considered the app bundle and nucleus will attempt to execute the specified file.
+
+If a file is provided in combination with the `-N`, `--no-bundle` option as specified below, app bundle file access restrictions will not apply.
+
+### `-h`, `--help`
+
+Prints CLI usage info including the spec options and executable name (or path), then exits with code `0`.
+
+While all implementations must implement a help option, it is not required to look the same provided it lists all the basic options in this spec.
+
+##### Example:
+
+```
+Usage: nucleus FILE [options]
+
+Options:
+    -h, --help          print this help menu
+    -v, --version       print the Nucleus version
+    -o, --output FILE   create a bundle with embedded nucleus at the specified file
+    -l, --linked        link nucleus instead of embedding
+    -z, --zip-only      create zip bundle without embedding
+    -N, --no-bundle     do not execute as a bundle
+```
+
+### `-v`, `--version`
+
+Prints the implementation and nucleus version, then exists with code `0`.
+
+The output should follow this format:
+```
+<impl name> v<impl version> implementing Nucleus v<nucleus version>
+```
+
+`<impl name>` should be the official name of the impl, but could be anything.
+
+Versions must be valid [SemVer](http://semver.org/) versions in the format of `major.minor.patch` with a pre-pended `v`.
+
+##### example:
+```
+rustyduk v0.0.0 implementing Nucleus v0.0.0
+```
+
+### `-o`, `--output` `FILE`
+
+Set an output filename for a zipped app bundle to be written to.
+
+Nucleus will be embedded and the file will be given a permissions mode of `777` on applicable operating systems.
+
+##### example:
+```
+nucleus ./my-app-folder -o my-app
+```
+
+### `-l`, `--linked`
+
+Requires the `-o`, `--output` option.
+
+Instead of embedding nucleus, insert a shebang link to it at the beginning of the zipped app bundle.
+
+The link should look like `#!/path/to/nucleus --\n`.
+
+##### example:
+```
+nucleus ./my-app-folder -l -o my-app-linked
+```
+
+### `-z`, `--zip-only`
+
+Requires the `-o`, `--output` option.
+
+Instead of embedding nucleus, only create a zipped app bundle.
+
+##### example:
+```
+nucleus ./my-app-folder -z -o my-app-bundle
+```
+
+### `-N`, `--no-bundle`
+
+Do not execute in bundled mode.
+
+This option requires that an exact file be specified for nucleus execute.
+
+Any app bundle file access limitations must not apply when executing in this mode.
+
+Useful for testing.