test -t 1 returns true when not attached to tty #4766
Description
Fish
$ fish --version
fish, version 2.7.1-836-g6f1ae79a
$ function is_attached_to_terminal; test -t 1; and echo yes; or echo no; end
$ echo | is_attached_to_terminal | cat
yes
Bash
$ bash --version
GNU bash, version 4.4.19(1)-release (x86_64-apple-darwin15.6.0)
$ is_attached_to_terminal() { test -t 1 && echo yes || echo no; }
$ echo | is_attached_to_terminal | cat
no