# Save a document as JSON

Write the document in a tab to a file as JSON, whatever format the tab is read from, print a file's tree as JSON from the shell, or copy one value of the document as JSON.

Whatever format a tab is read from, its document is a tree of JSON's values. aless writes that tree out as JSON. The example opens the tutorial's file, [`bookshelf-openapi.yaml`](https://aless.tabnas.dev/examples/bookshelf-openapi.yaml). That file is an OpenAPI document in YAML.

## Write the whole document

To write the document to a file, type `:w`, a space, and a filename, such as `:w bookshelf.json`, and then press `Enter`. aless says `Wrote bookshelf.json` on the status line.

Whichever node has the focus, aless writes the whole document, so you don't need to move the focus before you type `:w`. aless pretty-prints the JSON with two spaces a level. The JSON's keys keep the order they have in the source.

aless resolves a relative filename from the directory it started in. `:w` refuses a file that exists, so that a mistyped name doesn't overwrite an existing file. `:w!` writes over the file.

[Line mode](https://aless.tabnas.dev/how-to/display.html#data-mode-and-line-mode) shows the same JSON in the viewer, so you can read the JSON before you write it. In line mode, the tree keeps its folds. `m` switches line mode on and off.

## What the JSON holds

The file that `:w` writes holds the tree the viewer shows, not the text of the source:

- Comments aren't in the tree, so they aren't in the file.
- A number keeps its spelling where JSON spells it the same way, so `1.0` stays `1.0`. A spelling that JSON lacks gives the value it stands for, so `0x1F` becomes `31`. For more information, see [Formats](https://aless.tabnas.dev/reference/formats.html#numbers).
- A format whose tree has a shape of its own keeps that shape in the file. aless writes an XML file as element records, a Markdown file as its syntax tree, and a CSV file as an array of records. For more information, see [Formats](https://aless.tabnas.dev/reference/formats.html).

## Print the JSON from the shell

To get the same JSON in a script, pass `--print-json` and the file. aless prints the tree as JSON on standard output, and exits. The viewer doesn't start, so no terminal is needed, and the JSON can go to a pipe or a file. Here the start of the OpenAPI document's JSON goes to `head`:

```console
$ aless --print-json bookshelf-openapi.yaml | head -5
{
  "openapi": "3.0.0",
  "info": {
    "title": "Bookshelf demo API",
    "version": "1.0.0",
```

The JSON is the same JSON that `:w` writes. `-k`, `--grammar`, and the other input options work as they do for the viewer. The viewer's own options, such as `--depth`, make no difference. A `-` in place of the file reads standard input, as JSON unless `-k` names another format:

```console
$ printf 'name: aless\ntags: [tree, json]\n' | aless -k yaml --print-json -
{
  "name": "aless",
  "tags": [
    "tree",
    "json"
  ]
}
```

When the file can't be read or doesn't parse, aless prints the report on standard error, prints nothing on standard output, and exits with the status 1. A script can test for that status:

```console
$ aless --print-json broken.json; echo "exit status $?"
[tabnas/unexpected]: unexpected character(s): ]
  --> broken.json:3:36
  1 | {
  2 |   "title": "A Book of Examples",
  3 |   "tags": ["examples", "reference",]
                                         ^ unexpected character(s): ]
  4 | }
  5 |

  The character(s) ] do not match any rule alternative active at
  this position.

  --internal: tag=-; rule=val~o; token=#CS; plugins=--
exit status 1
```

For more information about the report, see [Find out why a file does not parse](https://aless.tabnas.dev/how-to/errors.html).

## Copy one value instead

`yy` copies the focused value as indented JSON. `yv` copies the same value as JSON on one line. When the focus is on a container, the value copied is the whole container, so `yy` on one path of an API description copies every operation under that path. For more information, see [Copy a value or its path](https://aless.tabnas.dev/how-to/copy.html).