[libsmartcols] watch vs tty column detection

[eMPee584]

Running lsblk under watch makes output overflow the terminal width; running outside of watch makes columns adjust appropriately.

watch -c -d -n 0.2 -- LIBSMARTCOLS_DEBUG_PADDING=on lsblk --paths \
--output VENDOR,MODEL,SERIAL,RO,RM,NAME,SIZE,FSUSE%,FSAVAIL,FSTYPE,LABEL,MOUNTPOINT,STATE

Use case: wanted to have a live view of plugged in USB pen drives (whilest flashing our https://schulstick.org/ ).. but some devices have insanely long serial numbers xD

[karelzak]

In this case, lsblk (and other tools) does not assume it's executed on the terminal and it does not restrict output and columns width. It's the same as "lsblk > file".

The ideal soution would be to improve watch(1) to execute commands in a own terminal (like script(1)), but it's not trivial ...

Anyway, you do not need watch(1) at all ;-), you can use bash loop + clear:

while true; do printf  "%${COLUMNS}s\n" "$(date)"; lsblk --paths \
  --output VENDOR,MODEL,SERIAL,RO,RM,NAME,SIZE,FSUSE%,FSAVAIL,FSTYPE,LABEL,MOUNTPOINT,STATE; sleep 0.2; clear; done

(the command printf is there only to provide date and demostrate it works).

For lsblk, we can add --output-width to restrict libsmartcols table formatting. I'll implement it as it seems usable in another use-cases too.

EDIT: I'll use --width to keep it shorter.

[eMPee584]

A loop is ok – but watch does the difference highlighting 😎
Thanks for adding the option though. What a dream to-the-point-feature request delivery .. may the universe expand this pattern to all sentient programs, and may many more feature requests be fulfilled in this way. What a contrast to systemd style RESOLVED WONTFIX 👌😏