Question

Why is Bash producing two different outputs for these two commands:

$ echo $(tput cols 2>/dev/null)
80
$ echo $(tput cols)
141

PS. Widen your terminal to have more than 80 columns (most shells default to 80).

Answer 1

It appears to be because both stdout and stderr have been redirected, so tput doesn’t know what terminal you want the info for.

$ tput cols >out; cat out       # works because stderr is still the terminal
118
$ tput cols 2>err               # works because stdout is still the terminal
118
$ tput cols >out 2>err; cat out # lost track of the terminal, going with default
80

Note that in your example, stdout is redirected implicitly by $().