The old "+1" syntax isn't generally used by gnu sort, although it does still support it. Instead, use the -k
option, as explained in the man and info pages.
sort -t "/" -k 3 logfile
This will sort from the start of the 3rd field to the end of the line. To force it to sort only within that field, use -k 3,3
According to the above, the 3rd field delimited by /
is (or at least starts with) the year. Is that what you want to sort by? You need to use -n
or one of sort's other numerical sort options if you want anything other than a lexical sort.
I highly recommend reading the info page for this command.