There are a host of problems with my solution. However it solves the posted issue (reporting cached hits) as I understand the snippet. If we assume that @completefile is a file slurp (i.e. @completefile = <$fh>), then this loop will output the last $exch match in the file. If I misunderstand the spec and each line of @completefile represents a file slurp (i.e. local $/; push @completefile,<$fh>), then a solution could be obtained using a g modifier (and likely an m to boot) on the regex and a while loop: 

foreach $exch(@exch) { 
    for($i=0; $i<=$#completefile; $i++) { 
        $su_adapter = undef;
        $su_date = undef;
        while($completefile[$i]=~ m/^.+\\(.+)_.+\..+?:(.+?)\s-\s(.+?)\
+s.+?\/$exch\s\|.+::(.*Up)\(\)/g) { 
            $su_adapter=$1; 
            $su_date=$2; 
        }
        print $su_adapter, $su_date;
    }
}

[download]

I disagree with your point about printing since I generally care as much about a failed match as a successful match, and as long as the OP clearly isn't using warnings, printing undefs (with formatting like perhaps a newline) is appropriate. In any case, were I to have coded this, it would look a lot more like 

foreach my $exch (@exch) {
    my ($su_adapter, $su_date);
    foreach (reverse @completefile) {
        last if ($su_adapter, $su_date) = /^.+\\(.+)_.+\..+?:(.+?)\s-\
+s(.+?)\s.+?\/$exch\s\|.+::(.*Up)\(\)/;
    }
    if (defined $su_adapter) {
        print "Last match for $exch: $su_adapter, $su_date\n";
    } else {
        print "No match for $exch\n";
    }
}

[download]

In the end, much of this is strictly academic, since this the OP never posted enough code to really understand what they intended.

In reply to Re^5: undef a variable for a loop by kennethk
in thread undef a variable for a loop by csiepka

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.