Acquire Terminal Width & Height

1. tput cols
   tput rows
   tput -S <<< cols
   tput -S <<< rows

    

2. stty size

    

3. echo $LINES
   echo $COLUMNS

   LINES & COLUMNS are not environment variables, they are just normal variables to bash, It's only available in interactive shell
   

   the checkwinsize option only initialize the variables after waiting for subshell to finish.

    

    

    $LINES and $COLUMNS are updated after SIGWINCH is sent, actually after any interactive command execution. If you try to update PS1 with trap SIGWINCH you can't use $LINES and $COLUMNS, they keep old values