sort takes an input file and sorts it, using either alphabetic sort (default) or numeric sort (-n option).
The current implementation of sort is simply a shell script which calls the usual unix sort(1).
Note that the -n option is only useful for generating pretty output. It should not be used with join.
sort only reads the standard input, so '<' must be used.
When using numeric sort (-n), only the first column is sorted numerically. For fixed vales of the first column, the rest of the line is sorted alphabetically.