DuckDB CLI skills

# 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