Sorry. I guess 3-char extensions are pretty pervasive:)

It might be a tad more efficient to use a hash instead of greping an array for the lookup.

sub wait_for_files{
    my %not_changed = %{ +shift };
    
    while( sleep 1 and keys %not changed ) {
        -e  and delete $not_changed{ $_ } for keys %not_changed;
    }
}
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