• This is a Shell written in C for Linux operating system.

• lol this is part of an assignment at college

• I wouldn't recommend anyone installing it. 😂
• Go use bash instead of this.

• My Ctrl+Z,Ctrl+C are Not working properly.
• Go to the folder you wish, And Run:

  $ git clone https://github.com/Abhinavreddy-B/C-Shell.git

• Compile as:

  $ make
  (or)
  $ make main

• Run As:

  $ ./main

• How To Exit?
  • I am not a VIM user, I provide a way to exit my Shell.
  • just press Ctrl+D

2021101034
├── commands
│   ├── commands.h
│   ├── bg.c
│   ├── cd.c
│   ├── discover.c
│   ├── echo.c
│   ├── fg.c
│   ├── history.c
│   ├── jobs.c
│   ├── ls.c
│   ├── pinfo.c
│   ├── pwd.c
│   └── sig.c
├── Helpers
│   ├── Helpers.h
│   ├── add_to_list.c
│   ├── check_invalid.c
│   ├── getinfo.c
│   ├── History.c               /* TO HANDLE HISTORY */
│   ├── interrupt_handlers.c
│   ├── ioredirect.c
│   ├── pipe.c
│   ├── process_creation.c
│   ├── splitter.c              /* split the command among cd,ls,echo,..... */
│   └── tokenize.c
├── io_module
│   ├── input.c                 /* Taking input ( raw mode ) and autocompletion */
│   ├── input.h
│   ├── print_error.c
│   ├── print_error.h
│   ├── prompt.c
│   └── prompt.h
├── Linked_list
│   └── ADT for Linked List
├── main.c
├── makefile
├── headers.h
├── README.md
└── README.pdf

commands: contains implementations of built-in commands

Helpers: contains some helper functions

Linked_list: contains ADT for linked list (used in storing background process data)

io_module: function for taking input, printing errors and prompt

$ make
(or)
$ make main

$ ./main

assuming precendence order is ';'>'&'>'|' > (spaces and tabs) > (io redirection) . So tokenising accordingly.

1. Spec1:
   • Assuming that < , > , >> would always be followed by a file name ( i.e commands like "cat < >" or "cat <" will give ambiguous results)
2. Spec2:
   • the commands when using pipe run one command after the other

     ~> sleep 5 | sleep 5
     

     takes 10 seconds to execute.
3. Spec4:
   • bg is having problems with "vi" / "vim" due to some unknown vi bugs.
4. Spec6:
   • Everything is implemented as mentioned in the PDF

assumed all lengths such as Maximum input size,Maximum directory path length,.... to be 1001

assuming precendence order is ';'>'&'>(spaces and tabs) . So tokenising accordingly.

Please use a terminal window of sufficient width so that text wrat does not cause any problem

1. cd:
   • Not handling ~ when ~ is not at the start of the path (similar to bash).
   • maximum length of paths is 1001 chars
2. echo:
   • printed as is irrespective of Quotes and newlines ( ",\n,').
   • handled space and '\t' characters similar to bash ( replace multiple space / tabs with single space ).
3. pwd:
   • Did not check for the number of arguments passed ( since bash also does the same ).
   • absolute path
4. ls:
   • implemented same as that of Bash.
   • assumed that there cant be paths like / , where there are some special files / folders which are not handlable.
   • if there are multiple files / folders as arguments , we printed in the same order as given to us ( Bash prints for files first and directories next ).
   • if the user name , or group name exceeds 15 characters , only the first 15 chars of their name are printed.
5. pinfo:
   • cannot read the executable path for certain processes like systemd ( pid - 1 ) , where user does not have appropriate permissions.
6. History:
   • even if the input has only a combination of spaces and tabs , they are being added to history.
   • even if input is an invalid command it is being added to history.
   • refraing from adding to history only when the new input is exact same as old one (including space / tabs ).
   • saving history in a hidden file .shell_history.tmp. any arbitrary changes made to this file while programme execution would not reflect and leads to unexpected errors.
7. Background commands:
   • running vi/vim as a background process is creating problems due to some issues with inputs (stdin) on some machines. All other external commands work perfectly.
8. Foreground processes:
   • The time taken printed is the sum of individual parts of command

   sleep 3 ; sleep 4
   would print the time taken as 7s