ttystate - Determine tty state

README.md

ttystate - Determine tty state

Example

$ ./ttystate.bash 0
tty
$ ./ttystate.bash 0 <ttystate.bash
redirect
$ echo | ./ttystate.bash 0
pipe

ttystate.bash

#!/usr/bin/env bash
# ttystate
# Copyright (c) 2019 Koichi OKADA. All rights reserved.
# This script is distributed under the MIT license.
#

function ttystate () # <var> <fd>
# Get tty state.
# Parameters:
#   <var> : Variable name for return value
#   <fd>  : Number of file descriptor
# Return:
#   Return tty, redirect or pipe to <var>.
{
  local -n VAR="$1"
  local STD=( /dev/stdin /dev/stdout /dev/stderr )
  local T P
  [ -t $2         ]; T=$?
  [ -p ${STD[$2]} ]; P=$?
  case "$T$P" in
    01) VAR=tty      ;;
    11) VAR=redirect ;;
    10) VAR=pipe     ;;
    *)  echo "Error: unknown ttystate: $T$P"; exit 1 ;;
  esac
}

if [ "$(readlink -f -- "$0")" = "$(readlink -f -- "$BASH_SOURCE")" ]; then
  ttystate STATE "$1"
  echo $STATE
fi