C-Shell

Making a shell in C programming language

Made by Vineeth Bhat (2021101103)

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Running shell

1. Run the makefile via $ make
2. Start executing shell as $ ./main
3. Enter commands separted by ; or & just as you would in a unix terminal

   • $ command1 arguments & command2 arguments

   • $ command1 arguments; command2 arguments ; command3 arguments ...

   • A command ending with a ; will be executed in the foreground while a command ending in & will executed in background. If no such character is present at the end, then the command is run in foreground.

   • If a foreground process takes more than 1s, then that is indicated in the terminal's prompt. If a series of ; separated processes are executed, then considers time taken by the most recently executed process.

   • I/O redirection works as follows -

     1. cmd > file : redirects stdout into the file (writes file)
     2. cmd < file : reads from file, i.e, takes stdin from file
     3. cmd >> file : Appends data to file

     (Works on assumption that user will give spaces around <, >, and >>)

   • Piping works as follows -

     cmd1 | cmd2 : redirects output of cmd1 into input of cmd2

   • Signals -

     1. ^C : Terminates running foreground process, if any.
     2. ^D : Logs out of shell
     3. ^Z : Pushes running foreground process to background.

   • Autocompletion -

     Whenever tab key is pressed it either -

     1. Displays all the possible files folders starting with the given starting characters (all files and folders if preceeded by a space or nothing) under the prompt.
     2. If there is only one possible file or folder, it is autocompleted in the terminal.
4. To remove all .o files, main file and history file (hidden) run $ make clean

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Commands

1. echo

   • Output : Prints the entered arguments by excluding extra spaces and tabspaces.

   • Syntax :

     $ echo <arguments>

   • Example :

     $ echo hello there!

     >>> hello there!

2. cd

   • Output : Changes current directory to given directory

   • Syntax :

     $ cd : changes to home directory

     $ cd ~ : changes to home directory

     $ cd file_path : changes to path based on characters such as . (current directory) and .. (parent directory)

     $ cd -

   • Example :

     $ cd ~

3. pwd

   • Output : Prints the present working directory

   • Syntax :

     $ pwd

   • Example :

     $ pwd prints /HOME/username/... if the present working directory is a descendant of the directory from which the shell was executed

     $ pwd prints /home/username/... otherwise

4. exit

   • Output : Quits shell

   • Syntax :

     $ exit

5. ls

   • Output :

     • Paths -

       • If no path is given, lists files and directories in current directory.

       • If path of a directory is given, lists files and directories in given directory.

       • If path of a file is given, lists information about the file

       • If the path is invalid, throws an error

     • Flags -

       • -l lists all relevant information about path

       • -a lists all the hidden files and folders too

   • Syntax :

     $ ls -<flags> <dir_name> : changes to home directory

6. pinfo

   • Output : Prints the relevant information about the given pid (taken as shell's pid if no pid is provided):

     • process id

     • process status (R for running, S for sleeping, Z for zombie; Append '+' if process is run in foreground)

     • memory usage

     • executable path

   • Syntax :

     $ pinfo <pid>

7. history

   • Output : Displays upto 10 previously executed commands in terminal. Included commands from previous runs of the shell as well.

   • Syntax :

     $ history

8. discover

   • Output :

     • Paths -

       • If no directory path is given, uses current directory

       • If no search path is given, lists files and directories in given directory based on flags

       • If the path is invalid, throws an error

     • Flags -

       • -f lists/searches only files

       • -d lists/searches only directories

     • CANNOT search for hidden files and folders

   • Syntax :

     $ discover -<flags> <dir_name> : changes to home directory

9. jobs

   • Output : Displays all processes running in background along with pid and status (running or stopped)

     • Flags -
       • -s print only stopped processes
       • -r print only running processed

   • Syntax :

     $ jobs -<flags>

10. sig

    • Output : Send the signal corresponding to the given signal number to the given job bumber (based on sequential order printed in jobs). Throws an error if either job number or signal number are invalid.

    • Syntax :

      $ sig <job_number> <signal_number>

11. fg

    • Output : Brings the running or stopped background job corresponding to job number to the foreground, and changes its state to running.

    • Syntax :

      $ fg <job_number>

12. bg

    • Output : Changes the state of a stopped background job to running (in the background).

    • Syntax :

      $ bg <job_number>

13. Any other process is run as in linux terminal using execvp

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Files

A filename refers to both the .c as well as the .h files

1. back_process

   • Functionality to run a process in background, handle termination of a background process and add ackground processes to a linked list for execution.

2. cd

   • Functionality to change directory

3. cmd

   • Functionality to execute a process in background, exit terminal and tokenise inputs
   • Functionality to parse I/O redirection, piping and signals (^C, ^D, ^Z)

4. discover

   • Functionality to search for a given file or directory based on input arguments and flags

5. dll

   • Functionality to create and manipulate linked lists, to store a structs of char* and int, in order to handle history queue and background process execution

6. echo

   • Functionality to print the given message after removing tabs and spaces

7. error_mes

   • Functionality to perror a message and exit terminal with EXIT_FALIURE : reserved for things which if not implemented, prevent the shell from functioning at all

8. fore_process

   • Functionality to execute a non-builtin command in foreground using execvp

9. headers

   • Lists all headers file which are imported in every file and the variables used throughout the shell

10. history

    • Functionality to display history command's outputs, add an input to the history queue, initiate history queue from hidden storage file from previous run of shell and store contents in hidden file upon exiting shell

11. ls

    • Lists files and directories in given directory, or lists information about given file, based on flags

12. main

    • No main.h exists. Main driver code.

13. path

    • Functionality to get relative path wrt root directory or current directory, and to get absolute path from relative path wrt root directory.

14. pinfo

    • Functionality to implement pinfo

15. prompt

    • Functionlity to display shell prompt

16. pwd

    • Functionality to display absolute path of present working directory

17. autocompletion

    • Functionality to implement autocompletion

18. bg

    • Functionality to implement bg command

19. fg

    • Functionality to implement fg command

20. sig

    • FUnctionality to implement sig command