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Write a configuration file

A variant of Write another file format

Write rows as key and value pairs or structured settings, such as a properties, INI, TOML or YAML file.

Status

In arcform

Runs as a SQL step

arcform carries it as a sql: step today.

The DuckDB step

Write rows as properties, INI, TOML and YAML settings files

SQL

CREATE TEMP TABLE settings AS SELECT * FROM (VALUES
  (1, 'db', 'host', 'localhost'), (2, 'db', 'port', '5432'), (3, 'app', 'name', 'orders "v2"')) t(pos, section, key, value);
-- a number is written bare and any other value as a double-quoted string, which TOML and YAML both read
CREATE TEMP TABLE shown AS
SELECT *, CASE WHEN try_cast(value AS BIGINT) IS NOT NULL THEN value ELSE to_json(value)::VARCHAR END AS literal,
       min(pos) OVER (PARTITION BY section) AS section_pos
FROM settings;
COPY (SELECT section || '.' || key || '=' || value FROM shown ORDER BY pos) TO '<your_scratch_dir>/out.properties' (FORMAT csv, HEADER false, QUOTE '', ESCAPE '', DELIMITER '~');
COPY (SELECT line FROM (
        SELECT DISTINCT section_pos, 0 AS o, 0 AS pos, '[' || section || ']' AS line FROM shown
        UNION ALL SELECT section_pos, 1, pos, key || ' = ' || literal FROM shown) ORDER BY section_pos, o, pos)
  TO '<your_scratch_dir>/out.toml' (FORMAT csv, HEADER false, QUOTE '', ESCAPE '', DELIMITER '~');
COPY (SELECT line FROM (
        SELECT DISTINCT section_pos, 0 AS o, 0 AS pos, '[' || section || ']' AS line FROM shown
        UNION ALL SELECT section_pos, 1, pos, key || ' = ' || value FROM shown) ORDER BY section_pos, o, pos)
  TO '<your_scratch_dir>/out.ini' (FORMAT csv, HEADER false, QUOTE '', ESCAPE '', DELIMITER '~');
COPY (SELECT line FROM (
        SELECT DISTINCT section_pos, 0 AS o, 0 AS pos, section || ':' AS line FROM shown
        UNION ALL SELECT section_pos, 1, pos, '  ' || key || ': ' || literal FROM shown) ORDER BY section_pos, o, pos)
  TO '<your_scratch_dir>/out.yaml' (FORMAT csv, HEADER false, QUOTE '', ESCAPE '', DELIMITER '~');
SELECT CASE WHEN ((SELECT content FROM read_text('<your_scratch_dir>/out.properties')) = 'db.host=localhost' || chr(10) || 'db.port=5432' || chr(10) || 'app.name=orders "v2"' || chr(10) AND (SELECT content FROM read_text('<your_scratch_dir>/out.toml')) = '[db]' || chr(10) || 'host = "localhost"' || chr(10) || 'port = 5432' || chr(10) || '[app]' || chr(10) || 'name = "orders \"v2\""' || chr(10) AND (SELECT content FROM read_text('<your_scratch_dir>/out.ini')) = '[db]' || chr(10) || 'host = localhost' || chr(10) || 'port = 5432' || chr(10) || '[app]' || chr(10) || 'name = orders "v2"' || chr(10) AND (SELECT content FROM read_text('<your_scratch_dir>/out.yaml')) = 'db:' || chr(10) || '  host: "localhost"' || chr(10) || '  port: 5432' || chr(10) || 'app:' || chr(10) || '  name: "orders \"v2\""' || chr(10)) THEN 'as expected' ELSE error('the properties, TOML, INI and YAML files were not written with their sections, bare numbers and quoted, escaped strings') 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 out.ini, out.properties, out.toml and out.yaml itself, in <your_scratch_dir>.
It needs nothing installed beyond DuckDB itself.
The statement checks its own result and raises an error when it is wrong: “the properties, TOML, INI and YAML files were not written with their sections, bare numbers and quoted, escaped strings”.
It passed on DuckDB v2.0.0 (Cyanoptera) d54cbbe3df.

What other tools call it

Meridian's classification; an independent blind rating agreed on 95.7% of 324 rows (variant, version 3).

Apache Hop (1)

Properties file Outputread 2026-09-27
Write key and value pairs to a Java properties file

Duckle (2)

TOMLread 2026-09-25
write rows as TOML under a rows key
YAMLread 2026-09-25
write rows as a top-level YAML array

Pentaho Data Integration (1)

Properties Outputread 2026-09-27
Write key and value pairs to a properties file

Talend (1)

tFileOutputPropertiesread 2026-09-27
Write key = value pairs to an .ini or .properties file

Background

In Apache Hop, the Properties Output transform writes rows of data to a Java properties file, taking the key from one field and the value from another.^[1] An INI (initialisation) file is a configuration file of plain text whose key–value pairs are organised in sections.^[2] TOML (Tom's Obvious, Minimal Language) aims to be a minimal configuration file format that is easy to read, designed to map unambiguously to a hash table.^[3]

When to use it

In Talend, the tFileOutputProperties component writes a configuration file of the .ini or .properties type, with text data organised as key = value.^[4] .properties files are mainly used in Java-related technologies to store the configurable parameters of an application.^[5] There is no Request for Comments (RFC) for .properties files, and their specification documents are not always clear.^[5]

INI is an informal format, so many varying specifications exist, called INI dialects.^[2] INI interpretations vary in whitespace preservation, field type information, case sensitivity and preferred comment delimiters.^[2] Find out which parser will read the file, and write for that parser's dialect, quoting and escaping values as it expects. (Meridian's view)

In a .properties file, keys with the same name are overwritten by the key that is furthest down the file.^[5] In TOML, defining a key multiple times is invalid.^[3] Deduplicate keys before writing a settings file. (Meridian's view) Apache Hop's Properties Output can update an existing properties file, leaving properties that the transform does not process unchanged.^[1]

The method

In INI, a section name appears on a line by itself in square brackets, and applies to all key–value pairs on the following lines until another section is declared.^[2]

Each line in a .properties file normally stores a single property, written as key=value, key = value, key:value, or a key and value separated by whitespace.^[5] In a .properties file, single or double quotes are considered part of the string, and the backslash is used to escape a character.^[5]

In TOML, the key, equals sign and value of a key/value pair must be on the same line, though some values can be broken over several lines.^[3] TOML basic strings are surrounded by quotation marks, and a quotation mark or backslash inside one must be escaped.^[3] TOML tables are defined by headers in square brackets on a line by themselves, and the key/value pairs within a table are not guaranteed to be in any order.^[3] TOML is case-sensitive, and a TOML file must be a valid UTF-8 encoded Unicode document.^[3]

YAML (YAML Ain’t Markup Language) is a human-friendly, cross-language, Unicode-based data serialisation language, broadly useful for needs that include configuration files.^[6] In YAML, the double-quoted style is the only style capable of expressing arbitrary strings, by using backslash escape sequences.^[6] The YAML 1.2 specification was published in 2009, and its primary focus was making YAML a strict superset of JSON.^[6]

Sources

[1]Write data to properties file | Apache Hopdocumentation
[2]INI file - Wikipediasecondary source
[3]TOML: English v1.0.0standard
[4]Properties components | Talend Components for Jobs Helpdocumentation
[5].properties - Wikipediasecondary source
[6]YAML Ain’t Markup Language (YAML™) revision 1.2.2standard