join is used to create a field separator (opposite: split )

code:

my $a='4,7,11,14';
print join(',',split(',',$a));
[download]

result:

4,7,11,14

code:

my @numbers=(4,7,11,14);
my $start='0 ';
my $middle=' 0 ';
my $end="\n";
print $start,join("$middle",@numbers),$end;
[download]

result:

0 4 0 7 0 11 0 14