I'm walking through the examples and exercises in "Effective Perl Programming" by Joseph N. Hall and Randal Schwartz (2 asides: 1) yeah, Merlyn and, 2) reading on my Kindle, where the formatting is inconsistent and some fairly odd typos mar the text; looks like it was translated to Kindle format by someone unfamiliar with Perl).

This script, pure ASCII -- or so I think, is adapted from an example on sorting:

#!/usr/bin/perl
use Modern::Perl;

say "\n\n\t sort on multiple keys";

my @first = qw(John Joe John Jon Fred Rich);
my @last = qw(Smith Smith Jones Jackson Jones Adler);

my @index = sort {
    $last[$a] cmp $last[$b]
    or
    $first[$a] cmp $last[$b]
} 0 .. $#first;

for (@index) {
    say "$last[$_], $first[$_]";
}

say "\n \t But, testing, single sort (cmp):";


my @sorted = sort { $a cmp $b  } qw(John Joe John Jon Fred Rich);
for (@sorted) {
    say "\t $_";
}


=head execution

         sort on multiple keys
Adler, Rich
Jackson, Jon
Jones, John
Jones, Fred
Smith, John
Smith, Joe

         But, testing, single sort (cmp):
         Fred
         Joe
         John
         John
         Jon
         Rich

## sort puts "John" before "Joe" in the first instance but not in the 
+second: Why?

=cut

[download]

Can someone point me to the document I failed to read or the section I failed to read carefully enough that explains the disparity in the output?

In reply to Variance in sort order (collation) {Solved: needed sharper eyes} by ww

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.