Thank you Ken. For wantarray, it's exactly answer what I want. I also tried a test.pl verify it. I understand PUSH and SET after reading your comments. My another question is about the reason of using the ++. If the 0(false) is added to 1, what's the incrementing for? It's not like an iterator's or a pointer's moving we normally see. The increasing didn't change anything seemingly.

For "++" sign in Perl, I only use it in some simple cases and seldom embedded it into a complicated expression. In some language, "++"'s action is dependent on the compiler's implementation and I should know the language very well or may easily make error. When I saw "$seen{lc($field)}++", I'm thinking which operator wll take the highest priority to interpreter, "($seen{lc($field)})++" or "$seen({lc($field)}++)". I decided to find some artical about Perl Ops priority to read first.

In reply to Re^2: What's this line means in HTTP::headers? by anaconda_wly
in thread What's this line means in HTTP::headers? by anaconda_wly

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.