Frequently Asked Question

How do I sort numerically, by column, or stably?

Plain sort orders lines lexicographically, so the numbers 1, 2, 10, 20 come out as 1, 10, 2, 20, which is rarely what anyone wants. sort -n sorts numerically and gets that right. sort -h understands human-readable suffixes like 4K, 2M, 1G, which is handy with du. sort -r reverses the order.

To sort by a particular column, use -k together with -t for the delimiter. sort -t: -k3 -n /etc/passwd sorts the password file numerically by UID (the third colon-separated field). Awkwardly, sort -k3 by default treats the rest of the line from field 3 onward as the sort key; use -k3,3 to mean only field 3. Finally, sort -s is a stable sort, equal keys preserve their original order, which lets you sort by one key, then re-sort by another to get a deterministic two-level ordering.