open(my $in, '<', 'Text_File.csv')
    or die "Cannot open Text_File.csv: $!";

open(my $out, '>', 'mask.spec')
    or die "Cannot open mask.spec: $!";

while (my $line = <$in>) { 
#my @fields = split (/(?<="),(?=")/, $line);
    my @fields = split(/,/, $line); 
    if (@fields == 4) { 
        printf {$out} "%s layernum %s datatype %s,%s", @fields; 
    } 
    elsif (@fields == 5) { 
        printf {$out} "%s layernum %s datatype %s text %s,%s", @fields;
    } 
}