# Write a file of any format

Publish / file

one writer that picks the format from the file name

Page: <https://meridian.online/operations/write-a-file-of-any-format>

## Status

Runs as a SQL step.

arcform carries it as a `sql:` step today.

## The DuckDB step

the writer is chosen from the file name

It reads the `orders` table the proofs share. Create it first:

```sql
CREATE TABLE orders AS SELECT * FROM (VALUES
  (1,  'Alice Ng',      'north', DATE '2026-01-03', 120.00, 'widget', 'a|b',   '{"channel":"web","items":[1,2]}'),
  (2,  'alice ng',      'north', DATE '2026-01-05',  80.50, 'gadget', 'b',     '{"channel":"shop","items":[3]}'),
  (3,  'Bob  Okafor',   'south', DATE '2026-01-05', 300.00, 'widget', 'a|c',   '{"channel":"web","items":[4,5,6]}'),
  (4,  'Carla Díaz',    'east',  DATE '2026-01-09',  NULL,  'gizmo',  NULL,    '{"channel":"web","items":[]}'),
  (5,  'Bob Okafor',    'south', DATE '2026-01-12',  45.25, 'gadget', 'c',     '{"channel":"phone","items":[7]}'),
  (6,  'Dev Patel',     'west',  DATE '2026-01-12', 510.00, 'widget', 'a',     '{"channel":"web","items":[8,9]}'),
  (7,  'Carla Diaz',    'east',  DATE '2026-01-20',  99.99, 'gizmo',  'b|c',   '{"channel":"shop","items":[10]}'),
  (8,  'Dev Patel',     'west',  DATE '2026-02-02', 510.00, 'widget', 'a',     '{"channel":"web","items":[8,9]}'),
  (9,  'Eve Larsen',    NULL,    DATE '2026-02-03',  15.00, 'gadget', NULL,    '{"channel":"web","items":[11]}'),
  (10, 'Alice Ng',      'north', DATE '2026-02-10', 220.00, 'gizmo',  'a|b|c', '{"channel":"phone","items":[12,13]}')
) t(order_id, customer, region, order_date, amount, product, tags, meta);
```

Then run the statement:

```sql
COPY orders TO '<your_scratch_dir>/w.parquet'; COPY orders TO '<your_scratch_dir>/w.json'; COPY orders TO '<your_scratch_dir>/w.csv';
CREATE TEMP TABLE result AS
SELECT (SELECT count(*) FROM glob('<your_scratch_dir>/w.*')) AS files,
       (SELECT count(*) FROM read_parquet('<your_scratch_dir>/w.parquet')) AS parquet_rows,
       (SELECT count(*) FROM read_json('<your_scratch_dir>/w.json')) AS json_rows,
       (SELECT count(*) FROM read_csv('<your_scratch_dir>/w.csv')) AS csv_rows;
SELECT * FROM result;
SELECT CASE WHEN ((SELECT files = 3 AND parquet_rows = 10 AND json_rows = 10 AND csv_rows = 10 FROM result)) THEN 'as expected' ELSE error('a file written by name alone is not in the format its name says') END AS verdict;
```

Replace `<your_scratch_dir>` with a directory of your own that you can write to before running the statement.

The statement writes `w.csv`, `w.json` and `w.parquet` itself, in `<your_scratch_dir>`.

It needs nothing installed beyond DuckDB itself.

## What other tools call it

Meridian's classification; an independent blind rating agreed on 86.2% of 312 rows (exact class, version 2).

- Azure Data Factory: [`Copy Activity`](https://learn.microsoft.com/en-us/azure/data-factory/copy-activity-overview) (read 2026-09-27)
- Alteryx Designer: [`Output Data`](https://help.alteryx.com/current/en/designer/tools/in-out-tools/output-data-tool.html) (read 2026-09-27)
- DuckDB: [`COPY`](https://duckdb.org/docs/current/sql/statements/copy) (read 2026-09-27)
- Apache NiFi: [`PutFile`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.PutFile/) (read 2026-09-27)
- Tableau Prep: [`Output`](https://help.tableau.com/current/prep/en-us/prep_build_flow.htm) (read 2026-09-27)
- VisiData: [`commit-sheet`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/modify.py#L362) (read 2026-09-23)