Bash Variables(Usable in scripts)-some may be already set and some not
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$BASH        - path to basIh binary
$BASH_SUBSHELL - bash sub-shell level
$BASH_VERSION  - show bash version
$DIRSTACK  - top value in directory stack
$EDITOR   - default editori
$EUID - effective identification number of current user
$FUNCNAME - current executed function name (call it in function to find out)
$GROUPS - groups user belongs to
$HOSTNAME - this value is called from bash by gethostname()
$HOSTTYPE - same effect as $MACHTYPE displays the system hardware type(eg.i686)
$IFS - determines recognition of fields or word boundaries in char strings
          default is whitespace 
$IGNOREEOF - how many EOFs to ignore before logging out ( Ctl-D )
$LC_COLLATE - set this to value of "C" and searching will include only capitals
                   like here : ls [A-M] will also print small letter by default.$LINENO - show line number reached in script ( must be called from script)
$OLDPWD - old working directory (previous directory that you were in)
$PIPESTATUS - array variable holding the exit status of last executed foreground                  pipe.(not status of last executed command)
$PPID - the process id of the parent process
$PS1 - the main prompt seen at the command line
$PS2 - secondary prompt when additional input is expected,">". ;)
$REPLY - if after specifying a "read" in a script,you dont add a variable to re               ad for assigning the input to,then this is the default location
               of the input is. 
$SHELLOPTS - shell options that are enabled--it is read-only.
$TMOUT - set this value to a number and use it in a script to act as a timeout.
              you dont have to call it after setting it,all "read" called 
                will timeout after $TIMEOUT secs.
$UID - user id number of the user.