# opens a "cursor" on the directory entries
# works kind of like open(...) but for directories rather
# than files

opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";

# calls readdir(DIR) in list context - so that means that
# all directory entries are returned at once.
# then it passes the array of local file names through grep

# grep selects members of an array based on the return
# value of the {...} bit.
#
# $_    - a member of the array returned by readdir(DIR)
#         i.e. the local name of a file in the directory $some_dir
#
# /^\./ - selects only local file names beginning with dots.
#         this is short for $_ =~ /^\./
#
# -f "$some_dir/$_"  - checks to see if the fully qualified path
#                      "$some_dir/$_" is an existing file.

@dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR); 

# like close() but for directories

closedir DIR;