# The build command

The build command is used to render your book:

    mdbook build

It will try to parse your `SUMMARY.md` file to understand the structure of your book and fetch the corresponding files. Note that files mentioned in `SUMMARY.md` but not present will be created.

The rendered output will maintain the same directory structure as the source for convenience. Large books will therefore remain structured when rendered.

#### Specify a directory

The `build` command can take a directory as an argument to use as the book's root instead of the current working directory.

    mdbook build path/to/book

#### --open

When you use the `--open` (`-o`) flag, mdbook will open the rendered book in your default web browser after building it.

#### --dest-dir

The `--dest-dir` (`-d`) option allows you to change the output directory for the book. Relative paths are interpreted relative to the book's root directory. If not specified it will default to the value of the `build.build-dir` key in `book.toml`, or to `./book`.

Note: The build command copies all files (excluding files with `.md` extension) from the source directory into the build directory.