# The spaces aren't really necessary.
my $months = 
"jan feb mar apr may jun jul aug sep oct nov dec";

my @sorted = sort{
	index( $months, lc(substr($a,0,3)), 0)
	<=>
	index( $months, lc(substr($b,0,3)), 0)
	|| $a cmp $b
	} @files; 

##</code><code>##

#! perl -sw
use strict;

sub shufl { $a = $_ + rand @_ - $_ and @_[$_, $a] = @_[$a, $_] for (0..$#_); return @_; }
sub rndtxt{ my $s=''; $s .= chr(65+rand 26) for 1 .. $_[0]; $s }

# Gen some test data - 1 filename for every day of the year
my @test =
	grep{ -1 == index('feb30feb31apr31jun31sep31nov31', $_) } # remove funnies
	map{
		local $.=$_;
		(map{$. . sprintf('%02d',$_)}1..31)
	} qw(jan feb mar apr may jun jul aug sep oct nov dec);

my @files;
push@files,@test for 1 .. $ARGV[0]||1; # duplicate to give n filenames/day
# and mix them up and add random stuff
@files =  	map{ $_ . rndtxt(8) } shufl @files;

my $months = "jan feb mar apr may jun jul aug sep oct nov dec";

my $start =  time; # Time it
my @sorted = sort{
	index( $months, lc(substr($a,0,3)), 0)
	<=>
	index( $months, lc(substr($b,0,3)), 0)
	|| $a cmp $b
	} @files; # sort them

print 'Sorting    ', scalar @sorted, ' filenames took ', time-$start, ' seconds.', $/;

my @months = qw(jan feb mar apr may jun jul aug sep oct nov dec);
my %monthindex; @monthindex{@months} = 0 .. $#months;

$start = time;
my @sorted2 =
	map $_->[0],
	sort { $a->[1] <=> $b->[1] || $a->[0] cmp $b->[0] }
  	map [ $_, $monthindex{lc substr $_, 0, 3}], # no point in lc the whole lot
   	@files;
print 'Sorting ST ', scalar @sorted, ' filenames took ', time-$start, ' seconds.', $/;
print 'The results of both sorts verify as ', ("@sorted" eq "@sorted2") ? "the same\n" : "different\n";

__DATA__
c:\test>202022
Sorting    366 filenames took 0 seconds.
Sorting ST 366 filenames took 0 seconds.
The results of both sorts verify as the same

c:\test>202022 10
Sorting    3660 filenames took 1 seconds.
Sorting ST 3660 filenames took 3 seconds.
The results of both sorts verify as the same

c:\test>202022 20
Sorting    7320 filenames took 5 seconds.
Sorting ST 7320 filenames took 7 seconds.
The results of both sorts verify as the same

c:\test>202022 30
Sorting    10980 filenames took 11 seconds.
Sorting ST 10980 filenames took 17 seconds.
The results of both sorts verify as the same

c:\test>202022 50
Sorting    18300 filenames took 29 seconds.
Sorting ST 18300 filenames took 43 seconds.
The results of both sorts verify as the same

c:\test>202022 100
Sorting    36600 filenames took 110 seconds.
Sorting ST 36600 filenames took 170 seconds.
The results of both sorts verify as the same

c:\test>

##</code><code>##

#! perl -sw
use strict;

sub shufl { $a = $_ + rand @_ - $_ and @_[$_, $a] = @_[$a, $_] for (0..$#_); return @_; }
sub rndtxt{ my $s=''; $s .= chr(65+rand 26) for 1 .. $_[0]; $s }

# Gen some test data - 1 filename for every day of the year
my @test =
	grep{ -1 == index('feb30feb31apr31jun31sep31nov31', $_) } # remove funnies
	map{
		local $.=$_;
		(map{$. . sprintf('%02d',$_)}1..31)
	} qw(jan feb mar apr may jun jul aug sep oct nov dec);

my @files;
push@files,@test for 1 .. $ARGV[0]||1; # duplicate to give n filenames/day
# and mix them up and add random stuff
@files =  	map{ $_ . rndtxt(8) } shufl @files;

my $months = "jan feb mar apr may jun jul aug sep oct nov dec";

my $start =  time; # Time it
my @sorted = sort{
	index( $months, lc(substr($a,0,3)), 0)
	<=>
	index( $months, lc(substr($b,0,3)), 0)
	|| $a cmp $b
	} @files; # sort them

print 'Sorting     ', scalar @sorted, ' filenames took ', time-$start, ' seconds.', $/;

my @months = qw(jan feb mar apr may jun jul aug sep oct nov dec);
my %monthindex; @monthindex{@months} = 0 .. $#months;

$start = time;
my @sorted2 =
	map $_->[0],
	sort { $a->[1] <=> $b->[1] || $a->[0] cmp $b->[0] }
  	map [ $_, index( $months, lc(substr($_,0,3)), 0)],
   	@files;
print 'Sorting mST ', scalar @sorted, ' filenames took ', time-$start, ' seconds.', $/;
print 'The results of both sorts verify as ', ("@sorted" eq "@sorted2") ? "the same\n" : "different\n";

__DATA__
c:\test>202022-3
Sorting     366 filenames took 0 seconds.
Sorting mST 366 filenames took 0 seconds.
The results of both sorts verify as the same

c:\test>202022-3 10
Sorting     3660 filenames took 1 seconds.
Sorting mST 3660 filenames took 2 seconds.
The results of both sorts verify as the same

c:\test>202022-3 100
Sorting     36600 filenames took 108 seconds.
Sorting mST 36600 filenames took 171 seconds.
The results of both sorts verify as the same

c:\test>