use strict;
use Data::Dumper;

# Uh, well spotted, typo fixed with the extra +
# which would have no effect anyway. :-)
# ysth suggested that putting () in map shortcircuts
# empty lines. It worked. Thanks. :-)
# Wow, even better, dropped that testing bit.

#my %hostlist = map { /^(\w+)\s(.*)/?($1,$2):() } (<DATA>);
my %hostlist = map { /^(\w+)\s(.*)/ } (<DATA>);

print Dumper(\%hostlist);

__DATA__
host1 1.1.1.1
host2 1.2.3.5