csv - Miller - Ignore valid field names when using -N

Question

I'm using miller to process some CSV files like so:

mlr --mmap --csv --skip-comments -N cut -f 2 my.csv

It works well, but some of the CSV files contain field names and some do not, which is why I'm using -N. In the files that have field names, they get printed in the output. You would think that having the headerless-csv-output bundled in the N flag they wouldn't, but they are. Maybe it's a bug? Anyway, how would do I prevent the field names from being printed? If the input needs to be altered somehow and piped in that's fine, but the output is being uniquely processed.

Here's the documentation I've been referencing:

• https://manpages.ubuntu.com/manpages/focal/man1/mlr.1.html#options
• https://miller.readthedocs.io/en/latest/reference.html

my.csv

################################################################
#                                                              #
#                                                              #
#                      BIG OL' COMMENT BLOCK                   #
#                                                              #
#                                                              #
################################################################
#
"first_seen_utc","dst_ip","dst_port","c2_status","last_online"
"2021-01-17 07:30:05","67.213.75.205","443","online","2021-06-24"
"2021-01-17 07:44:46","192.73.238.101","443","online","2021-06-24"

Expected output

67.213.75.205
192.73.238.101

Present output

dst_ip
67.213.75.205
192.73.238.101

Answer 1

If your first field is always a date, you can use it

mlr --csv --skip-comments -N filter -S '$1=~"^[0-9]{4}-"' then cut -f 2 input.txt

Answer 2

if you use N for a CSV that has a header, you will add an automatic numeric header and the the original header will be a data row. Using N you will have also --implicit-csv-header

+---------------------+----------------+----------+-----------+-------------+
| 1                   | 2              | 3        | 4         | 5           |
+---------------------+----------------+----------+-----------+-------------+
| first_seen_utc      | dst_ip         | dst_port | c2_status | last_online |
| 2021-01-17 07:30:05 | 67.213.75.205  | 443      | online    | 2021-06-24  |
| 2021-01-17 07:44:46 | 192.73.238.101 | 443      | online    | 2021-06-24  |
+---------------------+----------------+----------+-----------+-------------+

If you want an headerless output you must use only it. If you run

mlr --csv --skip-comments --headerless-csv-output cut -f dst_ip input.txt

you will have

67.213.75.205
192.73.238.101