Learning Perl, 5th Edition

Interpolating Arrays into Strings

Like scalars, array values may be interpolated into a double-quoted string. Elements of an array are automatically separated by spaces^[*] upon interpolation:

@rocks = qw{ flintstone slate rubble };
print "quartz @rocks limestone\n";  # prints five rocks separated by spaces

There are no extra spaces added before or after an interpolated array; if you want those, you’ll have to put them in yourself:

print "Three rocks are: @rocks.\n";
print "There's nothing in the parens (@empty) here.\n";

If you forget that arrays interpolate like this, you’ll be surprised when you put an email address into a double-quoted string:

$email = "[e-mail]";  # WRONG! Tries to interpolate @bedrock

Although we intended to have an email address, Perl sees the array named @bedrock and tries to interpolate it. Depending on our version of Perl, we’ll probably just get a warning:^[†]

Possible unintended interpolation of @bedrock

To get around this problem, we either escape the @ in a double-quoted string or use a single-quoted string:

$email = "fred\@bedrock.edu"; # Correct
$email = '[e-mail]';  # Another way to do that

A single element of an array will be replaced by its value, just as you’d expect:

@fred = qw(hello dolly);
$y = 2;
$x = "This is $fred[1]'s place";    # "This is dolly's place"
$x = "This is $fred[$y−1]'s place"; # same thing

Note that the index expression is evaluated as an ordinary expression, as if it were outside a string. It is not variable-interpolated first. ...