The special variable $" determines what character(s) will be used to join array elements when they're interpolated into a double-quoted string.

Consider the following example:

my @array = qw/1 2 3 4 5/;
print "@array\n";
{
    local $" = "\n";
    print "@array\n";
}
{
    local $" = " see perlvar ";
    print "@array\n";
}
{
    local $" = "";
    print "@array\n";
}
__OUTPUT__
1 2 3 4 5
1
2
3
4
5
1 see perlvar 2 see perlvar 3 see perlvar 4 see perlvar 5
12345
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Hope this helps!