-------------------------- Table 5.1 --------------------------

$#      the number of arguments
$*      all arguments to shell
$@      similar to $*; see Section 5.7
$-      options supplied to shell
$?      return value of the last command executed
$$      process-id of the shell
$!      process-id of the last command started with &
$HOME   default argument for cd command
$IFS    list of characters that separate words in arguments
$PATH   list of directories to search for commands
$PS1    prompt string, default '$ '
$PS2    prompt string for continued command line, default '> '