The line foreach $host (<@allhosts>) is just wrong. The diamond operator is for reading from filehandles; it has nothing to do with iterating over an array. You wanted for my $host ( @allhosts ).

Having said that, a better approach would be to rethink what you're doing and go at the problem another way.

• Read in the list of hosts from STDIN first and stash them in a hash (e.g. my %want; while( <STDIN> ) { chomp; $want{$_} = 1 }).
• Next read the lines of the other file and split off the first element; if that element exists $want{ $ele } then you print the line.