Compare two CSV files, and see exactly what changed.

Why a text diff is not enough

A line-by-line diff reports every line as changed when the rows are in a different order, when a column was added in the middle, or when the separator changed from comma to semicolon. The data may be identical; the diff is useless.

Comparing tables

1. Open the newer file and press ⌃⌘D (Compare with Another File). Choose the older file — or compare with whatever table is on the clipboard.
2. Choose how rows line up: by position, or by a key column such as customer_no, so re-sorted files still match. Columns line up by name, so moved columns do too.
3. Read the differences: changed values are marked character by character — 300.00 → 350.00 highlights only the digit that moved. Rows only in one file are listed.
4. Take changes across one value at a time, or a whole row at once.

Case, spacing and whole columns can be left out of the comparison, so a column of timestamps that always differs does not hide the change you are looking for.

From the command line

icsv --diff yesterday.csv today.csv

opens the first file and compares it with the second, ready to read.