If you're never going to call the sub from outside the BEGIN block then maybe something like:

    BEGIN {
        my $get_regexes = sub {
             ...
           return map {...}
        };
        ...
    }
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Which has the advantage of keeping the subroutine private.

Oh yes, don't forget that in recent perl you can do open my $fh, ..., which is far nicer than

    local *FH; 
    open FH, ...
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