The "EOUsage" is the terminator for what's referred to as a here document. Note the print STDERR <<EOUsage; line several lines above it. Basically, everything between that line and the terminator gets printed to STDERR. Try perldoc perldata for more info, search for the words "here document".

The quoted text seems lucid to me. Perhaps I can rephrase a little ? If this script exists on a unix box as /usr/local/bin/myscript, $0 could contain one of several values, depending on how it was called:

How script was startedContents of $0
$ myscriptmyscript
$ /opt/local/bin/myscript/opt/local/bin/myscript
$ cd /opt/local/bin;./myscript./myscript

The following bit: $0 =~ s#.*/##; is a regex that strips everything from the front of $0 until it reaches the last "/" character. So, if the script is named myscript, after this regex is run against $0, $0 would contain myscript, regardless of how it was called.

In reply to Re: Newbie need a clue by kschwab
in thread Here document syntax, what is $0 (was: Newbie need a clue) by nysus

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.