cat

Concatenates files by rows or columns.

Write with --output. A trailing path is not a positional argument. Input files are positional; the output path is not.

# Concatenate files by rows (vertical; default --mode rows)
undatum cat file1.csv file2.csv --mode rows --output output.csv

# Concatenate files by columns (horizontal)
undatum cat file1.csv file2.csv --mode columns --output output.csv

Reference

Reads: any readable format · Writes: any writable format; CSV/TSV/JSON/JSON Lines on stdout · Memory: streaming · Engines: python

undatum cat [OPTIONS] INPUT_FILES...

Argument	Description
INPUT_FILES...	Path(s) to input file(s). Multiple files can be specified. (required)

Option	Description	Default
-o, --output TEXT	Optional output file path. If not specified, prints to stdout.
--mode TEXT	Concatenation mode: 'rows' (default) or 'columns'.	rows
-d, --delimiter TEXT	CSV delimiter character (auto-detected when omitted).
--quotechar TEXT	CSV quote character (iterabledata default '"' when omitted).
--encoding TEXT	File encoding (e.g., 'utf8', 'latin1').
--verbose / --no-verbose	Enable verbose logging output.	--no-verbose
-F, --format-in TEXT	Override input file format detection (e.g., 'csv', 'jsonl').
--table, --sheet TEXT	Table or sheet name for multi-table sources (Excel, SQLite, lakehouse).
--start-page INTEGER	Sheet index (0-based) for Excel files.	0
--trust	Acknowledge pickle deserialization risk when reading pickle sources.
--on-error TEXT	Parse-error policy: raise (default), skip, or warn.
--error-log TEXT	Append parse errors as JSONL (use with --on-error skip or warn).
--flatten-nested	Unfold nested dict / array-of-dict fields into dotted paths (e.g. city.lat).
--max-nested-depth INTEGER	With --flatten-nested, maximum nest depth to unfold (engine default 5).
--keep-nested-parents / --no-keep-nested-parents	With --flatten-nested, keep parent dict/array fields alongside dotted children.	--keep-nested-parents
-O, --format-out TEXT	Output format (e.g. csv, jsonl, parquet). Defaults to the --output extension, or to the input's text format on stdout.

See also shared options.