Trying to understand sort and anonymous sub

[Dalton Marris]

I am trying to understand the use of "sub" in the second "foreach 
$daynum" loop in the code shown below.  I know it's an anonymous sub, 
but can't figure out why it's needed, if it indeed is.  I have read the 
perlref and perlsub documents, and googled for information, to no avail.

Some things I have noticed regarding the first and second "foreach 
$daynum" loops:

When I step through the first "foreach $daynum" loop with Komodo, it 
seems to hang on the "foreach" as each combination of $a and $b values 
is sorted.  Stepping continues after everything is sorted.  The 
resultant output file contains the following (as expected):

946684800|Holiday 1|Holiday 2
950486400|Holiday 3
954547200|Holiday 5
977702400|Holiday 7|Holiday 8
When stepping through the second "foreach $daynum" loop, it only takes 
one step before it continues on, so it appears to be faster.  However, 
it also results in an extra key, for some reason.  The resultant output 
file contains the following:

946684800|Holiday 1|Holiday 2
950486400|Holiday 3
954547200|Holiday 5
977702400|Holiday 7|Holiday 8
CODE(0x198f04c)
My questions:
(1) What should the "sub" be doing?
(2) Where is the "CODE(0x198f04c)" coming from?
TIA,
Dalton
#!/usr/bin/perl -w
use strict;
my $dayentry;
my $daynum;
my $dbrow;
my %dayinfo = (
    977702400 => [ "Holiday 7",
                   "Holiday 8" ],
    950486400 => [ "Holiday 3" ],
    946684800 => [ "Holiday 1",
                   "Holiday 2" ],
    954547200 => [ "Holiday 5" ],
);
open( DBFILE, ">dbfile1.txt" ) or die("Error: could not open 
\"dbfile1.txt\"\n" );

foreach $daynum (sort{$a<=>$b} keys %dayinfo ) {
    $dbrow = "$daynum";
    foreach $dayentry (@{$dayinfo{$daynum}}) {
        $dbrow = join('|',$dbrow,$dayentry);
    }
    # write new data to output file
    print( DBFILE "$dbrow\n" );
}
close( DBFILE );
open( DBFILE, ">dbfile2.txt" ) or die("Error: could not open 
\"dbfile2.txt\"\n" );

foreach $daynum (sort(sub{$a<=>$b}, keys %dayinfo)) {
    $dbrow = "$daynum";
    foreach $dayentry (@{$dayinfo{$daynum}}) {
        $dbrow = join('|',$dbrow,$dayentry);
    }
    # write new data to output file
    print( DBFILE "$dbrow\n" );
}
close( DBFILE );
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