How do I load this into a hash with one column .

You can't have a hash with just one column. Hash elements have to be key-value pairs, although the value may be anything you want (you don't really care anyway), including undef, as in the code suggested by jahero.

I think that, in such a case, most people use either undef or simply 1. The upside of using 1 is that testing the hash value will return a true value, so that you can test existence by a simple look up:

say "Found it" if $hash{$key};
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This is marginally useful in one-liners because it is less key stokes than:

say "Found it" if exists $hash{$key};
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which is the more standard way of testing a hash for existence.

You can use map, as shown by jahero, or you can use a for loop. Assuming the file name is stored in the $file_in variable, this may look like this:

my %hash;
open my $INPUT, "<", $file_in or die "Cannot open $file_in $!"; # the 
+die "..."  part is not needed if you use autodie.
while (my $line = <$INPUT>) {
    chomp $line;
    $hash{$line} = 1;  # or undef or anything you like for the value
}
close $INPUT;
# You can use %hash for lookup now
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Update: fixed a typo: $hash{$line} instead of $hash{line}. Thanks to vighneshmufc for pointing it out.