Re: Gettings LINES and COLUMNS from stderr instead of /dev/tty

[Martin Schulte]

Hello Chet,

on 2022-07-18 10:26:05 -0400 you wrote:

> On 7/16/22 11:18 AM, Martin Schulte wrote:
> > Hello,
> > 
> > I'm just wondering that bash (reproduced with 5.2-rc1 under Debian 11) 
> > seems to determine LINES and COLUMNS from stderr.
>
> ... 
> When it's not interactive, all bets are off, and stderr is usually
> a safe default. There's no consistent approach across shells.

At least I lost my bet ;-)

Since I still have the opinion that either stdout or /dev/tty should be asked 
to set the variables (because it's the "natural assumption" that you want to 
format what you write there) please consider the following script:

#!/bin/bash

shopt -s checkwinsize
( : ) # set LINES/COLUMNS for first time
while true; do
  if ((EPOCHSECONDS%86400==11655)); then
    printf -v msg '%S' "It's pi o'clock UTC"
  else
    printf -v msg '%(%T)T' $EPOCHSECONDS
  fi
  tput clear ; tput cup 0 $(((COLUMNS-${#msg})/2)) ; echo "$msg"
  sleep 1
done

It fails with a "bash: printf: `S': invalid format character" once a day but 
I've no chance to catch this error - either it is cleared on the screen or 
logging stderr breaks the output.

BTW: tput first tries stderr, then stdout, then stdin, then /dev/tty.

Best regards

Martin