The code below is less elegant than others in this thread. I understand qw// better now...

However, I do attempt to use the supplied sample data, account for 1 or 2 digit months and days and puke if I don't get a 4 digit year.

#!/usr/bin/perl -w

use strict;

my @test=(    "example: 10/29/2001",
        "example: 2/18/2000 3rd quarter",
        "example: 3/18/2000 4th quarter",
        "example: 4/18/2000 4th quarter",
        "example: 5/18/2000 4th quarter",
        "example: 6/18/2000 1st quarter",
        "example: 7/18/2000 1st quarter",
        "example: 11/18/2001 2nd quarter",
        "example: 01/18/1999 3rd quarter",
        "example: 02/18/1999 3rd quarter",
        "example: 3/18/1999 4th quarter",
        "example: 4/18/1999 4th quarter",
        "example: 5/18/1999 4th quarter",
        "example: 6/18/1999 1 quarter",
        "example: 7/18/1999 1 quarter",
        "example: 8/18/1999 1 quarter",
        "example: 9/18/1999 2nd quarter",
        "example: 10/18/1999 2nd quarter",
        "example: 11/18/1999 2nd quarter",
        "example: 12/18/1999 3rd quarter"
    );

sub my_compare(){
    # use "our" to limit scope to function but persist
    # map months to quarters
    our %quarters=(
        '6'=> 1,
        '06'=> 1,
        '7'=> 1,
        '07'=> 1,
        '8'=> 1,
        '08'=> 1,
        '9'=> 2,
        '09'=> 2,
        '10'=> 2,
        '11'=> 2,
        '12'=> 3,
        '1'=> 3,
        '01'=> 3,
        '2'=> 3,
        '02'=> 3,
        '3'=> 4,
        '03'=> 4,
        '4'=> 4,
        '04'=> 4,
        '5'=> 4,
        '05'=> 4
        );

# $a  and $b are given to us by sort
# they are the left & right sides of the comparision
# 
    my ($mon, $day);

    $a=~m|(\d*)/(\d*)/(\d*)|;
    $mon=length($1)<2?'0'.$1:$1;
    $day=length($2)<2?'0'.$2:$2;
    my $a3=$3 . $quarters{$mon}.$mon .$day;        
    die "bad year in $a" unless length ($3)==4;

    $b=~m|(\d*)/(\d*)/(\d*)|;
    $mon=length($1)<2?'0'.$1:$1;
    $day=length($2)<2?'0'.$2:$2;
    my $b3=$3 . $quarters{$mon}. $mon .$day;
    die "bad year in $b" unless length ($3)==4;

    return $a3 <=> $b3;
}

@test=sort(my_compare(), @test);
print join "\n", @test;
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