my $result = join $glue, @pieces;

The first argument to join is the glue, which may be any string. The remaining arguments are a list of pieces. join puts the glue string between the pieces and returns the resulting string:

my $x = join ":", 4, 6, 8, 10, 12;  # $x is "4:6:8:10:12"

In that example, we had five items, so there are only four colons. That is, there are four pieces of glue. The glue shows up only between the pieces, never before or after them. So, there will be one fewer piece of glue than the number of items in the list.

This means that there may be no glue at all, if the list doesn't have at least two elements:

my $y = join "foo", "bar";       # gives just "bar", since no fooglue is needed
my @empty;                       # empty array
my $empty = join "baz", @empty;  # no items, so it's an empty string

Using $x from above, we can break up a string and put it back together with a different delimiter:

my @values = split /:/, $x;  # @values is (4, 6, 8, 10, 12)
my $z = join "-", @values;   # $z is "4-6-8-10-12"

Although split and join work well together, don't forget that the first argument to join is always a string, not a pattern.

9.7. The split Operator		9.9. Exercises