bakunin:
Close, but not quite.
The sort key 4,4n treats the entire 4th field as a numeric field to be used as a sort key. The sort key 4n treats the data starting at the beginning of the 4th field to the end of the line as a numeric field to be used as a sort key. With either of these sort keys, lines that compare equal on that sort key will use the entire line as the secondary sort key treating the entire line as an alphanumeric string to be sorted in reverse order (since the -r option was also specified and was not associated with a particular sort key).

jimbojames:
Since the command ls ${DEST_LOCATION}/${FILES} provides a list of file pathnames (each line containing a single field unless there are spaces in the pathnames being sorted) the -k option to sort is just a distraction. If:

Code:

ls ${DEST_LOCATION}/${FILES} | sort -r -k 4n | head -1

really is the pipeline being executed, ls is not an alias adding options that will add fields to its output making the 4th field a numeric field, and that the expansion of ${DEST_LOCATION} does not start with a hyphen character; then the -k option to sort is meaningless, and the output will be the last file pathname in the list of files to which ls ${DEST_LOCATION}/${FILES} expands sorted alphabetically. Furthermore, unless one or more of the pathnames to which ${DEST_LOCATION}/${FILES} expands is a directory, the output will be equivalent to the simpler and faster pipeline:

Code:

ls ${DEST_LOCATION}/${FILES} | tail -1

I know that you inherited this pipeline and don't understand what it does. I don't understand why this command line is seemingly using options that make no sense. The only way for you to understand what is going on here (or for us to explain it to you), is for you to examine the contents of the pipes being passed through this pipeline and show us what you learn.

Try replacing:

Code:

ls ${DEST_LOCATION}/${FILES} | sort -r -k 4n | head -1

with:

Code:

ls ${DEST_LOCATION}/${FILES} | tee /tmp/pipe1 | sort -r -k 4,4n | tee /tmp/pipe2 | head -1

and show us the output produced and the contents of /tmp/pipe1 and /tmp/pipe2.