@files = ("a1.txt","a2.txt","a3.txt",...."an.txt");#n=50
foreach $file (@files)
{
   my ($h1, $t1) = split(/\./,$file);
   #use the value of $h1 to create a new array
   @{$h1}; #to create arrays @a1, @a2, @a3, ....@an
}