The way I iterate through an array and keep track of the previous element is like so:

my $previous = '';
foreach my $line (@arrayfile) {

   if ($line =~ m/WhateverIWantToMatch/) {
       print "$previous\n" if ($previous);
   }

   $previous = $line; #### This line now becomes the previous line for
+ the next array element seeing as ALL lines in the file will be proce
+ssed
}
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This is a quick example and presumes you are not going to find a match on the first line of the file.