You are giving Perl the code w to execute and the filename if (undef() eq undef()) {print "true" }else{ print "false"} as an argument to it. You probably wanted to say -we… Most of perl's switches are order sensitive.

strict catches this, FWIW:

$ perl -Mstrict -ew 'if(undef() eq undef()){print "true"}else{print "f
+alse"}'
Bareword "w" not allowed while "strict subs" in use at -e line 1.
Execution of -e aborted due to compilation errors.
$ perl -Mstrict -we 'if(undef() eq undef()){print "true"}else{print "f
+alse"}'
Use of uninitialized value in string eq at -e line 1.
Use of uninitialized value in string eq at -e line 1.
true

[download]

Makeshifts last the longest.

In reply to Re: Unexpected effect of -w with undef by Aristotle
in thread Unexpected effect of -w with undef by DrWhy

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.