牧羊人

The x operator can return repeated lists if used in list context and if the left operand is a literal list (i.e., wrapped in parentheses):

my @array = (1,2,3) x 2;
print "@array" # prints: 1 2 3 1 2 3

You need to be careful to put the left operand in parentheses for list repetition --- using a plain array will not behave as desired:

my @array = (1,12,42);
@array = @array x 2; print "@array\n"; # prints: 33

In this case, because the left operand is not in parentheses it is evaluated as a scalar, and an array in scalar context returns the number of elements in the array --- in this case 3 --- thus the x operator has returned the string '3' repeated twice.

Is this operator practical? Consider a case where you want to define a ten-element array and initialize each element to 1:

my @array = (1) x 10; # my @array = (1,1,1,1,1,1,1,1,1,1);

Another useful case is initializing a hash when we've read in (or otherwise obtained) a list of keys we wish to initialize to 1:

my @keys = qw(a b c d);
my %hash; @hash{@keys} = (1) x @keys;

Lastly, a minor cautionary note --- remember that 'x' is not the multiplication operator:

my $value = 15 x 2 / 3;
print "$value\n"; # prints: 505

Here the number 15 is treated as a string and repeated twice to get 1515 which is then treated as a number and divided by 3 to get 505 (rather than the result of 10 you might have wanted). This is one case where Perl's natural conversion between numbers and strings without warning can mean that a simple typo ('x' instead of '*') can lead to strange results and is difficult to track down. So, if you have calculations in your code and you are getting bizarre results you might want to check for this particular typo.