DuckDB CLI Specialist

Helps with data analysis, SQL queries and file conversion via DuckDB CLI.

Quick Start

Read data files directly with SQL

bash

# CSV
duckdb -c "SELECT * FROM 'data.csv' LIMIT 10"

# Parquet
duckdb -c "SELECT * FROM 'data.parquet'"

# Multiple files with glob
duckdb -c "SELECT * FROM read_parquet('logs/*.parquet')"

# JSON
duckdb -c "SELECT * FROM read_json_auto('data.json')"

Open persistent databases

bash

# Create/open database
duckdb my_database.duckdb

# Read-only mode
duckdb -readonly existing.duckdb

Command Line Arguments

Output formats (as flags)

Flag	Format
`-csv`	Comma-separated
`-json`	JSON array
`-table`	ASCII table
`-markdown`	Markdown table
`-html`	HTML table
`-line`	One value per line

Execution arguments

Argument	Description
`-c COMMAND`	Run SQL and exit
`-f FILENAME`	Run script from file
`-init FILE`	Use alternative to ~/.duckdbrc
`-readonly`	Open in read-only mode
`-echo`	Show commands before execution
`-bail`	Stop on first error
`-header` / `-noheader`	Show/hide column headers
`-nullvalue TEXT`	Text for NULL values
`-separator SEP`	Column separator

Data Conversion

CSV to Parquet

bash

duckdb -c "COPY (SELECT * FROM 'input.csv') TO 'output.parquet' (FORMAT PARQUET)"

Parquet to CSV

bash

duckdb -c "COPY (SELECT * FROM 'input.parquet') TO 'output.csv' (HEADER, DELIMITER ',')"

JSON to Parquet

bash

duckdb -c "COPY (SELECT * FROM read_json_auto('input.json')) TO 'output.parquet' (FORMAT PARQUET)"

Convert with filtering

bash

duckdb -c "COPY (SELECT * FROM 'data.csv' WHERE amount > 1000) TO 'filtered.parquet' (FORMAT PARQUET)"

Dot Commands

Schema inspection

Command	Description
`.tables [pattern]`	Show tables (with LIKE pattern)
`.schema [table]`	Show CREATE statements
`.databases`	Show attached databases

Output control

Command	Description
`.mode FORMAT`	Change output format
`.output file`	Send output to file
`.once file`	Next output to file
`.headers on/off`	Show/hide column headers
`.separator COL ROW`	Set separators

Queries

Command	Description
`.timer on/off`	Show execution time
`.echo on/off`	Show commands before execution
`.bail on/off`	Stop on error
`.read file.sql`	Run SQL from file

Editing

Command	Description
`.edit` or `\e`	Open query in external editor
`.help [pattern]`	Show help

Output Formats (18 available)

Data export

•csv - Comma-separated for spreadsheets
•tabs - Tab-separated
•json - JSON array
•jsonlines - Newline-delimited JSON (streaming)

Readable formats

•duckbox (default) - Pretty ASCII with unicode box-drawing
•table - Simple ASCII table
•markdown - For documentation
•html - HTML table
•latex - For academic papers

Specialized

•insert TABLE - SQL INSERT statements
•column - Columns with adjustable width
•line - One value per line
•list - Pipe-separated
•trash - Discard output

Keyboard Shortcuts (macOS/Linux)

Navigation

Shortcut	Action
`Home` / `End`	Start/end of line
`Ctrl+Left/Right`	Jump word
`Ctrl+A` / `Ctrl+E`	Start/end of buffer

History

Shortcut	Action
`Ctrl+P` / `Ctrl+N`	Previous/next command
`Ctrl+R`	Search history
`Alt+<` / `Alt+>`	First/last in history

Editing

Shortcut	Action
`Ctrl+W`	Delete word backward
`Alt+D`	Delete word forward
`Alt+U` / `Alt+L`	Uppercase/lowercase word
`Ctrl+K`	Delete to end of line

Autocomplete

Shortcut	Action
`Tab`	Autocomplete / next suggestion
`Shift+Tab`	Previous suggestion
`Esc+Esc`	Undo autocomplete

Autocomplete

Context-aware autocomplete activated with Tab:

•Keywords - SQL commands
•Table names - Database objects
•Column names - Fields and functions
•File names - Path completion

Database Operations

Create table from file

sql

CREATE TABLE sales AS SELECT * FROM 'sales_2024.csv';

Insert data

sql

INSERT INTO sales SELECT * FROM 'sales_2025.csv';

Export table

sql

COPY sales TO 'backup.parquet' (FORMAT PARQUET);

Analysis Examples

Quick statistics

sql

SELECT
    COUNT(*) as count,
    AVG(amount) as average,
    SUM(amount) as total
FROM 'transactions.csv';

Grouping

sql

SELECT
    category,
    COUNT(*) as count,
    SUM(amount) as total
FROM 'data.csv'
GROUP BY category
ORDER BY total DESC;

Join on files

sql

SELECT a.*, b.name
FROM 'orders.csv' a
JOIN 'customers.parquet' b ON a.customer_id = b.id;

Describe data

sql

DESCRIBE SELECT * FROM 'data.csv';

Pipe and stdin

bash

# Read from stdin
cat data.csv | duckdb -c "SELECT * FROM read_csv('/dev/stdin')"

# Pipe to another command
duckdb -csv -c "SELECT * FROM 'data.parquet'" | head -20

# Write to stdout
duckdb -c "COPY (SELECT * FROM 'data.csv') TO '/dev/stdout' (FORMAT CSV)"

Configuration

Save common settings in ~/.duckdbrc:

sql

.timer on
.mode duckbox
.maxrows 50
.highlight on

Syntax highlighting colors

sql

.keyword green
.constant yellow
.comment brightblack
.error red

External Editor

Open complex queries in your editor:

sql

.edit

Editor is chosen from: DUCKDB_EDITOR → EDITOR → VISUAL → vi

Safe Mode

Secure mode that restricts file access. When enabled:

•No external file access
•Disables .read, .output, .import, .sh etc.
•Cannot be disabled in the same session

Tips

•Use LIMIT on large files for quick preview
•Parquet is faster than CSV for repeated queries
•read_csv_auto and read_json_auto guess column types
•Arguments are processed in order (like SQLite CLI)
•WSL2 may show incorrect memory_limit values on some Ubuntu versions