Command:
echo "a" | tee `tty`
Output:
a
Command:
echo "a" | tee /dev/pts/0
Output:
a
a
File connected with current terminal is /dev/pts/0.
Shouldn't both commands produce same output? What am I missing here?
tee duplicates stdin to all file descriptors given on the command line and to stdout, so if one of the files it the current terminal (you can also use -) then input will be written twice on stdout.
In the first case, stdin is not connected to a tty (but to the output of the echo command), so tty gives not a tty. So the command becomes echo "a" | tee not a tty, and you will have three files (called "not" "a" and "tty") each containing "a", as well as "a" written to stdout.