use strict; 
use warnings; 
use Readonly; 
Readonly::Array my @array => ( 
    1,2,3,4,5,6, 
    1,2,3,4, 
    1,2,1,2,3,4,5,6,7,8,9, 
);  
Readonly::Scalar my $COMMA => q(,);  
 
my $beg      =  0; 
my $prev     =  0; 
my $position = -1; 
foreach my $elem (@array,0) { 
    if ($elem < $prev) { 
        my $end = $position; 
        my $substring = join $COMMA, @array[$beg..$end]; 
        print "($substring)  BEG=$beg END=$end\n"; 
        $beg = $position + 1; 
    } 
    $prev = $elem; 
    $position++; 
}