I didn't test this, but I think what you want is: 
$infile="hosts.txt";
open(INPUT, $infile) || die "Error opening $infile\n";
my @allhosts = <INPUT>;
close INPUT;
while ($approvhost=<STDIN>) 
    {
    chop($approvedhost); # or it won't partially match 
                         # your hosts entries becaus of 
                         # the training \n
    unless ($approvedhost) { last; } # so you can quit 
                                     # with a null entry
    foreach $host (@allhosts) # omit the <> you're not
                              # reading a file or stdin
        {
        if ($host =~ m/^$approvhost/)
            {
            print $host;
            }
        }
    }

[download]

In reply to Re: matching a line from one file in another by cormanaz
in thread matching a line from one file in another by New_to_this_stuff

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.