User guide
A Fastmash command has this shape:
fastmash [OPTIONS] OPERATION FIELDS [OPERATION FIELDS ...]
fastmash [OPTIONS] -g KEYS OPERATION FIELDS ...
fastmash [OPTIONS] MODE ...
fastmash [OPTIONS] top:N FIELD
fastmash [OPTIONS] compare BEFORE AFTER [rank RESULT [absolute|percent] [limit N]] OPERATION FIELDS ...
fastmash [INPUT OPTIONS] health [CONTROLS]
Fastmash reads records from standard input, splits each into fields, and applies the requested operations. It writes results to standard output and diagnostics to standard error, and reports success or failure through its exit status.
| Page | Covers |
|---|---|
| Fields and input | Field selectors, separators, headers, record terminators, comments, missing values |
| Quoted CSV and result names | Explicit CSV formats, quoting rules and stable output labels |
| Operations | Every summary statistic, with parameters and edge cases |
| Weighted mean | Contribution weights, complete-pair omission and numerical limits |
| Grouping and sorting | -g, -s, case-insensitive grouping, crosstab |
| Highest and lowest records | Complete-record selection, stable ties, groups and capacity limits |
| Dataset comparison | Before/after summaries, global key alignment and change ranking |
| Table health reports | Inspection, supplied validation rules and versioned TSV output |
| Per-row operations and modes | Rounding, binning, checksums, paths, cut, transpose, check, rmdup |
| Numbers, output and locales | Number formats, --format, --round, locales, portable results |
| Terminal color | Help, health and failure styling, detection and suppression |
| Errors, exit statuses and resources | What can fail, how it is reported, memory and disk use |
| Differences from GNU datamash | Every intentional difference |
fastmash --help prints a complete summary of operations and options.