Hi,

@rulefiles is an array containing the names of the *.rule" files in the folder.

for my $rulefile (@rulefiles) {
    # ...
}
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is a loop that goes over each of the items (file names) in the @rulefiles array, one after the other, assigns it to the $rulefile variable, so that each of the items can be manipulated with the $rulefile variable name within the body of the loop.

This is a simple example of a Perl one-liner using a similar construct:

$  perl -e 'for my $i (1, 4, 3, 2) {
     print "$i\n";
 }'
1
4
3
2

$
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In this example, the $i variable takes successively each value of the list (1, 4, 3, 2) and the body of the loop simply prints $i to the screen.