fetch info

[gareth]

hey guys, i'm struggling to find out how to do this, for example from
the help page:

http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/ports-using.html

# cd /usr/ports/sysutils/lsof
# make
>> lsof_4.57D.freebsd.tar.gz doesn't seem to exist in /usr/ports/distfiles/.
>> Attempting to fetch from ftp://lsof.itap.purdue.edu/pub/tools/unix/lsof/.
===>  Extracting for lsof-4.57


how do i figure out before typing make what that url is? (the filename
part seems to be under 'distinfo'). for instance i'd like to download
all the necessary tarballs before running 'portupgrade' to make the
actual upgrade quicker.