Matching against $_ is merely the default; the binding operator (=~) tells Perl to match the pattern on the right against the string on the left, instead of matching against $_.^[218] For example:

my $some_other = "I dream of betty rubble.";
if ($some_other =~ /\brub/) {
    print "Aye, there's the rub.\n";
}

The first time you see it, the binding operator looks like some kind of assignment operator. But it’s no such thing! It is simply saying, “This pattern match that would attach to $_ by default—make it work with this string on the left instead.” If there’s no binding operator, the expression uses $_ by default.

In the (somewhat unusual) example below, $likes_perl is set to a Boolean value according to what the user typed at the prompt. This is a little on the quick-and-dirty side because you discard the line of input itself. This code reads the line of input, tests that string against the pattern, then discards the line of input.^[219] It doesn’t use or change $_ at all: