Usage¶

We give a usage tutorial here; refer to the man page viat(1) for more details.

Command-line usage¶

First, a vault must be initialized:

viat init

The vault is determined by a .viat subfolder that contains config.toml and storage.toml files (JSON is also supported for both). We can immediately set attributes for any file on the file system:

$ viat update tractatus.pdf '{"author": "Ludwig Wittgenstein", "year": 1921}'
Warning: File 'tractatus.pdf' is not being tracked.
{"author": "Ludwig Wittgenstein", "year": 1921}

All stored attributes for the file get printed; in this case the only stored attributes are those we have just added. We also get a warning saying that the vault's tracker does not know about this file.

The role of the tracker is to enumerate the files that are explicitly tracked by the vault. The default glob-based tracking provider requires explicit patterns. We can track all PDF files in the root of the vault using the following configuration:

[tracker.glob]
patterns = ["*.pdf"]

With this, we can add new properties without warnings:

$ viat set tractatus.pdf rating 4
{"author": "Ludwig Wittgenstein", "year": 1921, "rating": 4}

The above worked because "true" is a valid JSON value; if we were to set a string instead, we would have to escape it in quotes, which is inconvenient. Instead, we can treat the value as a string by passing the --raw flag:

$ viat set --raw tractatus.pdf publisher 'Annalen der Naturphilosophie'
...

Scripting¶

Tracking is useful for ensuring consistency with the file system, but also for shell scripting. For example, the following command produces a table of variables:

$ viat shell-export
path=tractatus.pdf publisher='Annalen der Naturphilosophie' rating=4 author='Ludwig Wittgenstein' year=1921

This can be utilized in bash as follows:

viat shell-export | while read line; do
    eval "export $line"
    # The attributes are now exported as variables
done

In fish shell this is even simpler:

for line in (viat shell-export)
    eval "export $line"
    # The attributes are now exported as variables
end

If we add another file, zarathustra.pdf, and if the tracker lists it after tractatus.pdf, then Viat would try to reset the missing attributes to avoid reusing variables from the previous loop iteration:

$ viat shell-export
path=tractatus.pdf publisher='Annalen der Naturphilosophie' rating=4 author='Ludwig Wittgenstein' year=1921
path=zarathustra.pdf publisher= rating= author= year=

Schemas¶

It makes sense to utilize JSON schemas. Let us add the following to .viat/schema.json:

{
  "type":"object",
  "properties": {
    "year": {"type": "number"}
  }
}

Now we can no longer set the year to anything that is not a number:

$ viat set tractatus.pdf --raw year string
Error: Validation error for 'tractatus.pdf': data.year must be number.

The essence of the tool is that the attributes are stored in plain text formats that can be edited committed to version control. For example, .viat/storage.toml should now look as follows:

["tractatus.pdf"]
author = "Ludwig Wittgenstein"
year = 1921
rating = 4
publisher = "Annalen der Naturphilosophie"

If we manually change the year to "string", we will get a warning when loading the vault:

$ viat get tractatus.pdf rating
Warning: Validation error in stored data for 'tractatus.pdf': data.year must be number.
4

(Re)moving files¶

If we move tractatus.pdf to book.pdf, viat will no longer know about it:

$ viat get book.pdf rating
Warning: File 'book.pdf' is not being tracked.
Error: Attribute 'rating' has not been set for 'book.pdf'.

Such discrepancies can be determined relatively easily:

$ viat stale
tractatus.pdf
$ viat tracked --no-data
book.pdf

For such cases, we provide the helpers viat mv and viat rm, but otherwise avoid being too clever.

Programmatic usage¶

The programmatic usage is straightforward enough because of the API reference. Here is a brief continuation of the above example:

vault = autoload_vault()

assert vault.tracker.is_tracked('tractatus.pdf')

# This context manager validates and writes the file upon exiting.
# If no mutators have been used, no validation and writing is performed.
with vault.storage as conn:
    # The inner lock-based context managers allow either read-only or read-write operations.

    # Readers are Mapping instances.
    with conn.get_reader('tractatus.pdf') as reader:
        print(mut['year'])

    # Mutators are MutableMapping instances.
    with conn.get_mutator('tractatus.pdf') as mut:
        mut['year'] = 1921