How to make `column -t` ignore lines with specific characteristics

text formatting

I just thought how neat it would be to pipe my /etc/fstab through column -te to get a nicely formatted table.
But column of course has no way to discern comment lines and mountpoint definitions, so the comments are also split at every whitespace and formatted into table columns:

#                                          /etc/fstab:                  static   file                                      system     information.
#
#                                          Use                          'blkid'  to                                        print      the           universally   unique      identifier  for       a
#                                          device;                      this     may                                       be         used          with          UUID=       as          a         more  robust     way  to  name  devices
#                                          that                         works    even                                      if         disks         are           added       and         removed.  See   fstab(5).
#
#                                          <file                        system>  <mount                                    point>     <type>        <options>     <dump>      <pass>

#                                          /                            was      on                                        /dev/sda2  during        installation
UUID=8fa99d69-8dac-4aca-bb61-90f753ba5169  /                            btrfs    defaults,subvol=@rootfs,metadata_ratio=6  0          1
#                                          /home                        was      on                                        /dev/sda2  during        installation
UUID=8fa99d69-8dac-4aca-bb61-90f753ba5169  /home                        btrfs    defaults,subvol=@home                     0          2

Is there a way to make column only format lines that don't start with a #?

Edit: It seems I need to clarify that the example above is in fact a valid fstab. Btrfs has subvolumes that can be mounted separately with the subvol and subvolid mount options.
That also means that the devices in the first column of the fstab are not necessarily unique.

Best Answer

I think the pragmatic solution will be to let column do its thing on the whole file, and then simply collapse any multiple spaces in the comment lines

column -t /etc/fstab | sed '/^#/ s/ \{1,\}/ /g'

Otherwise, I can't see any way to do it besides numbering the lines, processing the comment and non-comment lines separately, and then sticking it all back together, e.g.

sort -nk1,1 \
<(nl -nln /etc/fstab | grep -vE '^[[:digit:]]+[[:space:]]+#'| column -t | sed 's/ \{1,\}/\t/') \
<(nl -nln /etc/fstab | grep -E '^[[:digit:]]+[[:space:]]+#') \
| cut -f2-
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