G'day v_ryan,

Welcome to the monastery.

The '.' in a regex doesn't match a newline unless you use the 's' modifier, so you can lose the '\n' and the '$' - you also don't need the '?'.

The only reason for the grep length is so that you don't pass the initial zero-length string to the map: a slice is shorter.

Running the two dumps for comparison:

...
dump { map { /(.+)\n/ => [ /^interesting line (.+?)$/mg ] }
       grep length, split /^Index: /m };

dump { map { /(.+)/ => [ /^interesting line (.+)/mg ] }
       (split /^Index: /m)[1,-1] };
...
[download]

gives identical output:

$ pm_golf_1038627.pl
{ "file1.txt" => [1, 2], "subdir/file2.txt" => ["A1", "A2"] }
{ "file1.txt" => [1, 2], "subdir/file2.txt" => ["A1", "A2"] }
[download]