Sort & uniq in Linux shell

Question

What is the difference between the following to commands?

sort -u FILE

sort FILE | uniq

Answer 1

Beware! While it's true that "sort -u" and "sort|uniq" are equivalent, any additional options to sort can break the equivalence. Here's an example from the coreutils manual:

For example, 'sort -n -u' inspects only the value of the initial numeric string when checking for uniqueness, whereas 'sort -n | uniq' inspects the entire line.

Similarly, if you sort on key fields, the uniqueness test used by sort won't necessarily look at the entire line anymore. After being bitten by that bug in the past, these days I tend to use "sort|uniq" when writing Bash scripts. I'd rather have higher I/O overhead than run the risk that someone else in the shop won't know about that particular pitfall when they modify my code to add additional sort parameters.