I want to strip trailing stuff from a host name. To clarify, running this test program t1.pl: 

use strict;
use warnings;
use Test::More;

my @expected = (
   [ 'abc',             'abc'  ],
   [ 'abc.bill.com',    'abc'  ],
   [ 'abc.bill.com.au', 'abc'  ],
   [ 'xy42.com',        'xy42' ],
   [ 'x_y.com',         'x_y'  ],
   [ 'x-y.com',         'x-y'  ],
   [ '',                ''     ],
   [ '.',               ''     ],
   [ 'a.',              'a'    ],
   [ '-.',              '-'    ],
   [ '_.',              '_'    ],
   [ '.a',              ''     ],
   [ 'f',               'f'    ],
   [ 'f.1',             'f'    ],
   [ 'f.1.2',           'f'    ],
   [ 'f.1.2.3',         'f'    ],
   [ 'f.1.2.3.4',       'f'    ],
   [ 'f.1.2.3.4.5',     'f'    ],
   [ 'f.1.2.3.4.5.67',  'f'    ],
   [ 'ABC.123.456',     'ABC'  ],
);

plan tests => scalar(@expected);

for my $e (@expected) {
   my ( $got, $exp ) = @{$e};
   $got =~ s/\..*$//;
   is( $got, $exp, "'$e->[0]'" . ' -> ' . "'$got'" );
}

[download]

produces: 

1..20
ok 1 - 'abc' -> 'abc'
ok 2 - 'abc.bill.com' -> 'abc'
ok 3 - 'abc.bill.com.au' -> 'abc'
ok 4 - 'xy42.com' -> 'xy42'
ok 5 - 'x_y.com' -> 'x_y'
ok 6 - 'x-y.com' -> 'x-y'
ok 7 - '' -> ''
ok 8 - '.' -> ''
ok 9 - 'a.' -> 'a'
ok 10 - '-.' -> '-'
ok 11 - '_.' -> '_'
ok 12 - '.a' -> ''
ok 13 - 'f' -> 'f'
ok 14 - 'f.1' -> 'f'
ok 15 - 'f.1.2' -> 'f'
ok 16 - 'f.1.2.3' -> 'f'
ok 17 - 'f.1.2.3.4' -> 'f'
ok 18 - 'f.1.2.3.4.5' -> 'f'
ok 19 - 'f.1.2.3.4.5.67' -> 'f'
ok 20 - 'ABC.123.456' -> 'ABC'

[download]

I'm pretty sure I can assume my input is just an alphanumeric host name, for example fred42 or fred.com but not 192.0.2.16 say. I further doubt I need to deal with ports :80 or ?query or other guff. Though the above crude hack will probably be adequate for my needs, I'm interested to learn how other folks might tackle this sort of problem.

In reply to Extracting a bald host name by eyepopslikeamosquito

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