Category: LPIC-1

$BASH_VERSION                    # bash version
$EDITOR                          # default editor
$GROUPS                          # membership in groups
$HISTFILE                        # user shell`s history file
$HISTSIZE                        # how many commands can be stored in bash $HISTFILE
$HOME                            # home directory
$HOSTNAME                        # hostname
$LANG                            # locale for the shell
$LC_*                            # locale settings that override $LANG
$LC_ALL                          # 
$LD_LIBRARY_PATH                 # paths to search for libraries
$PATH                            # paths to search for commands, priority order
$PS1                             # 
$PS2                             # 
$PWD                             # users working directory
$SHLLVL                          # current shell level
$TZ                              # current time zone if different from system time zone
$UID                             # user id
$VISUAL                          # 

readlink /bin/sh           # to which shell points /bin/sh 
echo $SHELL                # current shell 
echo $BASH_VERSION         # bash version
uname                      # distribution
uname -r                   # kernel version
uname -a                   # detailed kernel information
echo hello you             # output some text 
echo \[some \'content\'\]  # escape special characters: *?[]'"\$;&()|^<>
 
pwd                        # current directory
cd ~                       # cd to home 
cd $HOME                   # cd to home 
cd -                       # cd to home and print home dir location
type echo                  # shell built in or external command