SmallShell:smash

1
Small-Shellsmash

• Your assignment is to build a program smash'
  that will implement the following shell services
  
• Run programs in foreground and background
• List all processes that currently run in the
  background.
• Kill a process running in the background.
• Kill or suspend programs running in foreground
  mode using signals.
• Move programs that run in foreground mode to
  background mode and vice versa.

2
There are two types of commands that
smashshould understand

• External commands the command name is the name
  of an executable file.
• Internal commands commands that are "built-in"
  in the smash' shell.

3
Execution mode for external commands

• Foreground a command is given in the following
  form smashgtgt ltcommand_namegt
  ltlist_of_parametersgt. In this mode smash' does
  not return the prompt until the executable file
  that corresponds to the command finishes or it is
  interrupted by a signal.
• Background a command is given in the same format
  as in the foreground mode, but the last parameter
  in the parameter list should be '. The can
  be attached to the last parameter.

4
List of Internal commands you are required to
implement

• bye terminate smash'. All background processes
  should be terminated. (Note that the real shell
  does not do this).
• jobs list of all background jobs in the
  following format ltpidgt ltcommand namegt, in the
  order they entered the background list.
• S_jobs list of all suspended jobs in the
  following format ltpidgt ltcommand namegt, in the
  order they entered the suspended processes list.
• kill terminate the process corresponding to the
  specified pid by sending SIGTERM signal.
• bg passes a suspended process to run in
  back-ground mode. Incase their is no suspended
  process, a compatible message should be
  displayed.
• fg passes the most recent process running in
  back-ground mode to run in fore-ground mode.
  Incase their is no process running in back-ground
  mode, a compatible message should be displayed.

5
Signal Catching

• Implementation of the CTRL-C signal sending
  operation
• smash does not terminate after a CTRL-C
  operation.
• Back-ground running process (child) is not
  affected by a CTRL-C operation.
• A fore-ground running process terminates after a
  CTRL-C operation (like in the Unix).
• Implementation of the CTRL-Z signal sending
  operation
• Back-ground running process (child) is not
  affected by a CTRL-Z operation.
• A fore-ground running process is suspended and
  enters the suspended processes list.
• kill  system call
• Terminate processes in running in the
  back-ground corresponding to the specified pid.
• Uses SIGTERM signal that is caught by the
  process.