Save yourself some typing and use an array :-)

my @bytes = $address =~ /(\d+)\.(\d+)\.(\d+)\.(\d+)/;
my $hex_addr = sprintf "%02x.%02x.%02x.%02x", @bytes;
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Save yourself even more typing and make one expression of it.

my $hex_addr = sprintf "%02x.%02x.%02x.%02x", $address =~ /(\d+)\.(\d+
+)\.(\d+)\.(\d+)/;
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As you seem to be absolutely sure on the address format, split() will do:

my $hex_addr = sprintf "%02x.%02x.%02x.%02x", split /\./, $address;
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I'm sure others would recommend use of inet_aton(), from Socket.pm, because it's more flexible in what it accepts for an IP address. Unfortunately for us, if produces a string of 4 packed bytes, but it's nothing unpack() can't easily handle.

use Socket;
my $address = '127.1';
my $hex_addr = sprintf "%02x.%02x.%02x.%02x", unpack 'C*', inet_aton($
+address);
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And if you prefer uppercase hex instead of lowercase, use '%02X' instead of '%02x' in the sprintf() template.