# When sorting lists of files, I want the index file to always come first.
if ($c =~ /^index\./) {
    return -1;
}
elsif ($d =~ /^index\./) {
    return 1;
}

##</code><code>##

$ perl PM1021473_3_unstable.pl
index.0001 afile      article    -1
index.0001 index.0005 article    -1
index.9999 index.0005 article    -1

##</code><code>##

#!/usr/bin/perl
#
#   PM1021473_3_unstable.pl
#
use strict; use warnings;
use HTML::Entities;

while (<DATA>) {
    s/\s+$//;
    my @args = split /\s+/,$_;
    push @args, my_sort(@args);
    printf "%-10s %-10s %-10s %d\n", @args;
}

... your sort routine ...

__DATA__
index.0001 afile      article
index.0001 index.0005 article
index.9999 index.0005 article

##</code><code>##

sub my_sort_article {
  my ($c,$d,$type) = @_;
  $c = lc($c);
  $d = lc($d);

  my $t = my_sort_index($c, $d);
  return $t if $t;

  # Written with the help of kent/n in #perl on freenode.
      
  for ($c, $d) {
    s/<.+?>//g; # Strip out any html tags.
    s/\s*\b(A|a|An|an|The|the)(_|\s)//xi; # Strip off leading articles (in English).
    decode_entities($_);
  }
  if ( $c =~/^((\d|,|\.)+)(.*)$/ && $d =~ /^((\d|,|\.)+)(.*)$/) {
    # Get the leading number.
    (my $e = $c) =~ s/^((\d|,|\.)+)(.*)$/$1/;
    (my $f = $d) =~ s/^((\d|,|\.)+)(.*)$/$1/;

    # Take any commas out of the number.
    s/,//g for ($e,$f);

    # Get the remaining parts of the string.
    (my $g = $c) =~ s/^((\d|,|\.)+)(.*)$/$3/;
    (my $h = $d) =~ s/^((\d|,|\.)+)(.*)$/$3/;

    # First compare the numbers, then compare the remaining parts of the string.
    $e <=> $f || $g cmp $h
  }
  else {
    $c cmp $d;
  }
}

sub my_sort_name {
  # When I sort by name I prefer lastname firstname.
  # I have not yet written this to account for Sr., Jr., or Roman numerals after the last name.
  my ($c,$d,$type) = @_;
  $c = lc($c);
  $d = lc($d);

  # ?Did you really want this check for name sorting?
  my $t = my_sort_index($c, $d);
  return $t if $t;
      
  for ($c,$d) {
    s/\|.+$//;
    $_ = join(' ', (reverse split(/(?:_|\s)(?=[^_\s]+$)/, $_,2))) if $_ !~ /^_/;
    s/^_//;
    s/^(A|a|An|an|The|the)(_|\s)//;
  }
  return $c cmp $d;
}

##</code><code>##

sub split_out_leading_number {
    my $s = shift;
    if ( $s =~/^((\d|,|\.)+)(.*)$/) {
        my ($leading_number, $rest) = ($1,$3);
        # Take any commas out of the number.
        $leading_number =~ s/,//g;
        return ($leading_number, $rest);
    }

    die "split_out_leading_number received bogus input '$s'!\n";
}

##</code><code>##

sub my_sort_article {
  my ($c,$d,$type) = @_;
  $c = lc($c);
  $d = lc($d);

  my $t = my_sort_index($c, $d);
  return $t if $t;

  # Written with the help of kent/n in #perl on freenode.
      
  for ($c, $d) {
    s/<.+?>//g; # Strip out any html tags.
    s/\s*\b(A|a|An|an|The|the)(_|\s)//xi; # Strip off leading articles (in English).
    decode_entities($_);
  }
  if ( $c =~/^((\d|,|\.)+)(.*)$/ && $d =~ /^((\d|,|\.)+)(.*)$/) {
    my ($num1, $text1) = split_out_leading_number($c);
    my ($num2, $text2) = split_out_leading_number($d);

    # First compare the numbers, then compare the remaining parts of the string.
    $num1 <=> $num2 || $text1 cmp $text2
  }
  else {
    $c cmp $d;
  }
}

##</code><code>##

my @list = ( qw( apple Alpha aLBAtross aLbAcOre etc... ) );
my @result = sort {uc($a) cmp uc($b)} @original;

##</code><code>##

my @list = (
   [qw( APPLE     apple )],
   [qw( ALPHA     alpha )],
   [qw( ALBATROSS aLBAtross )],
   [qw( ALBACORE  aLbAcOrE)],
   etc...
);

##</code><code>##

my @result = sort { $a->[0] cmp $b->[0] } @list;

##</code><code>##

my @list = (
   [qw( ALBACORE  aLbAcOrE)],
   [qw( ALBATROSS aLBAtross )],
   [qw( ALPHA     alpha )],
   [qw( APPLE     apple )],
   etc...
);

##</code><code>##

my @list = ( qw( apple Alpha aLBAtross aLbAcOre etc... ) );

# Convert our list into the ( [APPLE apple], ... ) form with map:
@result = map { [ uc($_), $_ ] } @list;

# Now sort the list:
@result = sort {$a->[0] cmp $b->[0]} @result;

# Now convert the resulting list back into (aLbAcOrE aLBAtross...) format:
@result = map { $_->[1] } @result;

##</code><code>##

my @list = ( qw( apple Alpha aLBAtross aLbAcOre etc... ) );
my @result = map {$_->[1] }              #     .sgnirts desacreppu eht lla tou pirts #
             sort {$a->[0] cmp $b->[0]}  #  neht dna ,sgnirts desacreppu eht no tros #
             map { [ uc($_), $_ ] }      # ,gnirts eht fo noisrev desacreppu eht dda #
             @list;                      #                             ,tsil a neviG #