Linux Terminal Check stdin, stdout and stderr

When we want to check whether current terminal is attached to stdin, stdout and stderr streams or not, we can use the below codes. I tried with piping, and redirection so both works well.

As seen in below 6 usages, stdin is not listed in output of commands except first one. Because stdin is used by piping or redirection.

$  ([ -t 0 ] && echo stdin; [ -t 1 ] && echo stdout; [ -t 2 ] && echo stderr; echo hello)

stdin
stdout
stderr
hello
$ echo hello | ([ -t 0 ] && echo stdin; [ -t 1 ] && echo stdout; [ -t 2 ] && echo stderr; cat)

stdout
stderr
hello
$ ([ -t 0 ] && echo stdin; [ -t 1 ] && echo stdout; [ -t 2 ] && echo stderr; cat) <<<"hello"

stdout
stderr
hello
$ ([ -t 0 ] && echo stdin; [ -t 1 ] && echo stdout; [ -t 2 ] && echo stderr; cat) <<<$(echo hello)

stdout
stderr
hello
$ ([ -t 0 ] && echo stdin; [ -t 1 ] && echo stdout; [ -t 2 ] && echo stderr; cat) < foo.txt

stdout
stderr
Hello World
$ ([ -t 0 ] && echo stdin; [ -t 1 ] && echo stdout; [ -t 2 ] && echo stderr; cat) < <(cat foo.txt)

stdout
stderr
Hello World

Check current tty

TTY is a teletypewriter which is a terminal used from 1840. This word is still used today as virtual terminal.

$ tty

/dev/ttys000

List tty

$ who

kenanhancer console  Jun 30 16:25 
kenanhancer ttys000  Jul 11 02:25
$ w

 2:36  up 10 days, 10:12, 2 users, load averages: 1.60 1.50 1.54
USER     TTY      FROM              LOGIN@  IDLE WHAT
kenanhancer console  -                30Jun22 10days -
kenanhancer s000     -                 2:25       - w
$ ps

  PID TTY           TIME CMD
91820 ttys000    0:00.10 -bash
88521 ttys002    0:00.04 /usr/local/bin/bash -l
$ ls -l /dev/fd

total 0
crw--w----   1 kenanhancer  tty    0x10000000 11 Jul 02:38 0
crw--w----   1 kenanhancer  tty    0x10000000 11 Jul 02:38 1
crw--w----   1 kenanhancer  tty    0x10000000 11 Jul 02:38 2
drw-r--r--  67 kenanhancer  staff        2144 11 Jul 02:16 3
dr--r--r--   1 root         wheel           0 30 Jun 16:24 4

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