Well, getting rid of the $ isn't too bad. Just nail it after you read in the list. (TIMTOWTDI, but this is simple and effective):

my @computers = grep { /\$$/ } @users;
s/\$$// foreach @computers;         # remove trailing $
@computers = join("\n",@computers);
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As for gethostbyname, it returns an array of IP addresses for the hostname (remember, there may be more than one). An easy way to cope is to move the elements you want using perlfunc:splice:

@addr = gethostbyname($hostname);    # note: an array now
splice(@addr, 0, 4);                 # get rid of other stuff
foreach (@addr)
{
    print OUT join('.', unpack('C4', $_)), "\n";
}
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HTH