Curious tput behavior, with stderr redirection
bash, io-redirection
Solution
A quick `strace` run suggests that `tput` tries to determine the terminal width on `stdout` first, and if that fails, it falls back to `stderr`. So, in the failing case both are redirected, and `tput` (apparently) assumes a default of 80 columns.
Problem
I'm trying to use `tput` in a Bash script, and doing my best to avoid random error spew. To that end, I wrote the following line: ``` COLS="$(tput cols 2> /dev/null)" ``` To my surprise, when I run this, `COLS` is consistently set to `80`, no matter what the width of my terminal window happens to be. (For the sake of demonstration, my terminal happens to be 115 columns wide.) To figure out what was going on, I tried a few things on the command-line: ``` $ tput cols 115 $ tput cols | cat 115 $ echo "$(tput cols)" 115 $ tput cols 2> /dev/null 115 $ echo "$(tput cols 2> /dev/null)" 80 ``` So, `tput` seems to be succeeding in figuring out the terminal characteristics when its stderr is redirected, or when it is embedded in a process substitution, but not both. How odd! I tested this on both Linux and OS X, and the behavior is the same. What is going on here? And as a practical matter, what's the best way to get `tput` to work while suppressing stderr spew? Note: I know about `$COLUMNS`. I'm specifically interested in using `tput`.