-d                 (Used to invoke perl with the debugger)
 h                  Prints out a help message.
 T                  Stack trace.
 s                  Single step: executes until next statement
 n                  Next: executes over subroutines until next statement
 f                  Finish: excecute until the end of the current program
 c                  Continue: execute until next breakpoint
 c line             Continue: execute until specified line
 <CR>               Repeat last n or s.
 l min+incr         List incr+1 lines starting at min
 l min-max          List lines in indicated range
 l line             List just indicated line
 l                  List next window
 -                  List previous window.
 w line             List window around line
 l subname          List subroutine
 /pattern/          Regexpr search forward for pattern
 ?pattern?          Regexpr search backward for pattern
 L                  List line which have breakpoints or actions
 S                  List names of all subroutines
 t                  Toggle trace mode on or off.
 b line condition   Set a breakpoint
 b subname cond     Set breakpoint at first line of subroutine
 d line             Delete breakpoint at line (or next breakpoint)
 D                  Delete all breakpoints
 a line command     Set an action for line
 A                  Delete all line actions.
 < command          Set and action to happen before debugger prompt
 > command          Set and acction to happen after debugger prompt
 V package          List a variables in package.
 ! number           Redo debugging command.
 ! -number          Redo command that was that many commands ago
 H -number          History of last number of commands
 q or ^D            Quit
 command            Execute command as perl statement
 p expr             Print to /dev/tty regardless of STDOUT
 Modifying the Debugger