$echo $

$BASH                 $HOME                 $PPID
$BASH_ARGC            $HOSTNAME             $PS1
$BASH_ARGV            $HOSTTYPE             $PS2
$BASH_COMMAND         $IFS                  $PS4
$BASH_LINENO          $L3_HOME              $PWD
$BASH_SOURCE          $L3_PARENT_TTY        $RANDOM
$BASH_SUBSHELL        $L3_SESSION_ID        $SECONDS
$BASH_VERSINFO        $L3_TAMPERED_EDITORS  $SHELL
$BASH_VERSION         $LANG                 $SHELLOPTS
$BLOCKSIZE            $LINENO               $SHLVL
$COLUMNS              $LINES                $SSH_CLIENT
$COMP_WORDBREAKS      $LOGNAME              $SSH_CONNECTION
$DIFFNAME             $MACHTYPE             $SSH_TTY
$DIR                  $MAIL                 $TERM
$DIRSTACK             $MAILCHECK            $TIME
$EUID                 $MM_CHARSET           $UID
$FTP_PASSIVE_MODE     $OLDPWD               $USER
$GROUPS               $OPTERR               $_
$HISTCMD              $OPTIND               $editor_file
$HISTFILE             $OSTYPE               $editor_name
$HISTFILESIZE         $PATH                 $old_file
$HISTSIZE             $PIPESTATUS

/home/user