Interactive User Defined Shell

Instructions:
  1)run make all and then ./shell
  2)"exit" to terminate shell program


1)Shell Prompt with username and Operating system name appears.Current directory also appears.
  First time when shell is invoked,that directory is considered root or "~",and hence any inner directories follow pattern from here.


2)pwd
  - Shows currect working directory with respect to root directory of system(not shell)


3)echo 
  INPUT                                                                 OUTPUT 
  echo argument                                        ->               argument
  echo arg1        arg2                                ->               arg1 arg2
  echo "arg1          arg2"                            ->               arg1          arg2
  echo 'arg1          arg2'                            ->               arg1          arg2


4)ls
  INPUT                                                                 OUTPUT 
  ls                                                   ->               (Regular ls output)
  ls file1 file2 file3....                             ->               (ls output on each file-any number of arguments)
  ls dir file file2                                    ->               (ls output within dir and on each file)
  ls -[al]                                             ->               (Works on individual file also)
  																		                                  (Hidden files appear only with -a flag)
  																		                                  (Output looks exactly like original shell, with symmetry in file sizes also)
  ls ~
  ls ~/path...


 5)
  cd directory name
  cd ./../~ 
  cd ~/path...
  (works beyond ~ directory also)

6)pinfo command (user defined)
pinfo : prints the process related info of your shell program.
Ex: <Name@UBUNTU:~> pinfo
pid -- 231
Process Status -- {R/S/S+/Z} memory
- 67854 {Virtual Memory}
- Executable Path -- ~/a.out
-pinfo <pid> : prints the process info about given pid.
Ex: <Name@UBUNTU:~>pinfo 7777
pid -- 7777
Process Status -- {R/S/S+/Z} memory
- 123123 {Virtual Memory}
- Executable Path — /usr/bin/gcc


7)Background processes: Any command invoked with "&" is treated as background
command. This implies that this shell will spawn that process and doesn't wait for
the process to exit. It will keep taking user commands
  If the background process exits then the shell displays the appropriate
message to the user.
eg.
  emacs with pid 456 exited normally
  To run a command in background:
  
  command & 

8)Semi colon seperated commands work

9)BONUS Remindme:
  remindme [time] "[message]"

10)BONUS clock:
  clock -t [gap] -n [duration]


Redirection:
1) > is for redirecting output to a file(replacing)
2) >> is for redirecting output to a file(appending)
3) file name within double quotes is accepted
4) ls > "file  name" or ls>"file name" or ls      >"adsads" all cases work
5) wc -l < filename > outputfile or wc -l > outputfile < filename (for input + output redirection)