A read through Operator Precedence and Associativity in perlop would probably be informative. You have used the low-precedence or instead of the high-precedence ||. Alternatively, you can always use parentheses. 
my $hostname =
 gethostbyaddr(inet_aton($data[$ip_address_pos]), AF_INET)
         || "Can't resolve $data[$ip_address_pos]: $!\n";

my $hostname =
 (gethostbyaddr(inet_aton($data[$ip_address_pos]), AF_INET)
         or "Can't resolve $data[$ip_address_pos]: $!\n"
 );

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#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In reply to Re: Forgot variable syntax for $var = funct() or "Funct failed\n"; by kennethk
in thread Forgot variable syntax for $var = funct() or "Funct failed\n" / Any experience with is_hostname() by vlturner

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