I may be misunderstanding what you're asking, but to get only 1 column, you can just split the line as you read it.

open(HOSTFILE,"<$hostfile");
        foreach (<HOSTFILE>){
                if($_ =~ m/^#/){next;}
                if($_ =~ m/^\s$/){next;}

# Insert this line to split by whitespace
my @lineParts = split (/\s+/, $_);

#                push (@hostcontents,$_);

# Push [0] first column (ip), or use [1] for second column (hostname)
push (@hostcontents,$lineParts[0]);
        }
close(HOSTFILE);
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