| # `canon` — canonicalise a CSV export |
|
|
| Downstream tools need one boring, byte-stable TSV. Write an executable script at |
| `bin/canon` (shebang, `chmod +x`) that is invoked as: |
|
|
| ``` |
| ./bin/canon <input.csv> <output.tsv> |
| ``` |
|
|
| ## Input |
|
|
| UTF-8 CSV, possibly with a byte-order mark, possibly CRLF, RFC 4180 quoting: |
| fields may be quoted, may contain commas, doubled quotes (`""`) and embedded |
| newlines. The first record is the header. |
|
|
| ## Output |
|
|
| UTF-8 **without** a BOM, `\n` line endings, tab-separated, one line per record, |
| header first. Fields are written verbatim — never re-quoted, never trimmed — |
| except for the numeric normalisation below. Column order is preserved. |
|
|
| ## Numeric normalisation |
|
|
| A field is numeric when the whole field matches |
| `^[+-]?(\d+(\.\d*)?|\.\d+)([eE][+-]?\d+)?$`. Numeric fields are rewritten in |
| plain decimal notation with no exponent, no leading `+`, no leading zeros, and |
| no trailing zeros after the decimal point: |
|
|
| | input | output | |
| | --- | --- | |
| | `1.50` | `1.5` | |
| | `1.0` | `1` | |
| | `1e3` | `1000` | |
| | `2.5e-3` | `0.0025` | |
| | `+5` | `5` | |
| | `007` | `7` | |
| | `-0` | `0` | |
|
|
| Every other field is copied unchanged. |
|
|
| ## Ordering |
|
|
| Sort the data records by field 0, then by field 1, comparing the **normalised |
| strings** in byte order (so `"10"` sorts before `"9"`). The sort must be stable. |
|
|
| ## Errors |
|
|
| On any error, print exactly one line to stderr, exit with the given code, and do |
| **not** create the output file: |
|
|
| | condition | stderr line | exit | |
| | --- | --- | --- | |
| | input path does not exist | `no such file: <input path as given>` | `2` | |
| | two header names collide case-insensitively after trimming | `duplicate column: <name as written in the later header field>` | `3` | |
| | a record's field count differs from the header's | `malformed row: line <n>` | `4` | |
|
|
| `<n>` is the 1-based physical line number where the offending record starts |
| (so a record whose first line is the third line of the file reports `3`). |
|
|
| On success exit `0` and print nothing to stderr. |
|
|
| ## Notes |
|
|
| - `python` and `python3` are both on `PATH`; standard library only, no network. |
| - `data/orders.csv` is a sample with a BOM and CRLF endings. |
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|
