You are helping the user convert a data file from one format to another using DuckDB.
Input file: $0
Output file: ${1:-}
Step 1 — Resolve input and output
Input: $0. If it's a bare filename (no /), resolve to a full path with find "$PWD" -name "$0" -not -path '*/.git/*' 2>/dev/null | head -1.
Output: If $1 is provided, use it as the output path. If not, default to the same stem as the input with a .parquet extension (e.g., data.csv → data.parquet).
Infer the output format from the output file extension:
| Extension | Format clause |
|---|---|
.parquet, .pq | (default, no clause needed) |
.csv | (FORMAT csv, HEADER) |
.tsv | (FORMAT csv, HEADER, DELIMITER '\t') |
.json | (FORMAT json, ARRAY true) |
.jsonl, .ndjson | (FORMAT json, ARRAY false) |
.xlsx | (FORMAT xlsx) — requires INSTALL excel; LOAD excel; |
.geojson | (FORMAT GDAL, DRIVER 'GeoJSON') — requires LOAD spatial; |
.gpkg | (FORMAT GDAL, DRIVER 'GPKG') — requires LOAD spatial; |
.shp | (FORMAT GDAL, DRIVER 'ESRI Shapefile') — requires LOAD spatial; |
Step 2 — Convert
Run a single DuckDB command. Prepend extension loads as needed based on both the input and output formats.
duckdb -c "
<EXTENSION_LOADS>
COPY (FROM '<INPUT_PATH>') TO '<OUTPUT_PATH>' <FORMAT_CLAUSE>;
"
For remote inputs (s3://, https://, etc.), prepend the same protocol setup as read-file:
| Protocol | Prepend |
|---|---|
s3:// | LOAD httpfs; CREATE SECRET (TYPE S3, PROVIDER credential_chain); |
gs:// / gcs:// | LOAD httpfs; CREATE SECRET (TYPE GCS, PROVIDER credential_chain); |
https:// / http:// | LOAD httpfs; |
If the user mentions partitioning (e.g., "partition by year"), add PARTITION_BY (col) to the format clause. This only works with Parquet and CSV output.
If the user mentions compression (e.g., "use zstd"), add CODEC 'zstd' for Parquet output.
Step 3 — Report
On success, report:
- Input file and detected format
- Output file, format, and size (
ls -lh) - Row count if quick to compute
On failure:
duckdb: command not found→ delegate to/duckdb-skills:install-duckdb- Missing extension → install it and retry
- Input parse error → suggest the user check the input format or try
/duckdb-skills:read-filefirst to inspect it