This is "comma operator". The "true" or "false" of the "while" only depends upon the state of $test2.

Oh, completely missed that.. All my tests had the second file longer than the first. ++ for the explanation! If I may take another moment of your time, I tried fixing that code from before, although now I think that I'm using one of those endless loops you adviced against: 

while (my ($test1, $test2) = (scalar <$fh1>, scalar <$fh2>)) {
   last unless defined $test1 or defined $test2;
   ...
}

[download]
I figure that the simplest fixes (for me, that is: Feel free to kick me on the right path) would be to either use the defined-or on the results of the readlines, replacing the undefs with the empty list, or move everything into a sub.

..actually, rather than talk about it:

defined-or'ing 

while ( my $test1, $test2 ) = (scalar <$fh1> // (), scalar <$fh2> // (
+) ) {
    ...
}

[download]
sub'd 
sub read_double_file {
    my ($fh1, $fh2)                 = @_;
    my ($line_file_1, $line_file_2) = (scalar <$fh1>, scalar <$fh2>);

   (defined $line_file_1 or defined $line_file_2) ? ($line_file_1 //= 
+'', $line_file_2 //= '') : ();
}

while ( my ($line_from_1, $line_from_2) = read_double_file($fh1, $fh2)
+ ) {
    ...
}

[download]
Is there a better approach? (For whatever reason, trying to solve this has been quite fun -- I'm even thinking about meddling with objects, just so I don't have to pass the filehandles over and over to the subs) Are the attempts so far horribly, terribly wrong?

In reply to Re^3: Reading two text files parallelly... by Hugmeir
in thread Reading two text files parallelly... by biswanath_c

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.