SP9144/C-Shell

Course by Dr. PK Reddy | Monsoon 2020 | A user-defined interactive C shell program

C-Shell

This is a Linux Shell implemented in C.

Running the Shell

make
./shell_yeah

Exiting from the Shell

quit

Commands

• ls [-l -a] <dir1> <dir2> - List files and Directory

  • ls: List of all the files and directories in the current directory in alphabetical order
  • ls -a: Hidden files
  • ls -l: Long listing
  • ls -al/l -la/ls -l -a/ls -a -l: Long listing with hidden files

• cd <dir> - Change Directory

  • cd ..: Change to previous directory
  • cd .: Remain in current directory
  • cd: Change to directory to ~/

• echo [arguments] - Print in Terminal

  • echo: Print "\n"
  • echo "text": Print "text"
  • echo 'text': Print 'text'
  • echo text: Print text

• history [number] - Display History of Commands

  • history: Last 10 commands
  • history [1-20]: Last n commands

• pwd - Present Working Directory

• pinfo [pid] - Process Information

  • pinfo: Process information about the shell
  • pinfo <pid>: Process information about process with given pid

• setenv [var] [value] - Sets value of environment variable

  • setenv [var]: Default value = " "
  • setenv [var] [value]: var = value

• unsetenv [var] - Unsets value of environment variable

• jobs - Prints a list of all running jobs

• kjobs [job_num] [sig_num] - Sends signal val to that process with job_num

• overkill - Kills all background process

• bg [job_num] - Changes a Stopped background job to a Running

• fg [job_num] - Brings a background job to foreground

• <command> & - Run Process in Background

• <command1> | <command1> - Multiple Piping allowed

• Redirection - I/O Redirection allowed

  • <: Input redirection
  • >: Output redirection
  • >>: Append

Signals

• CTRL-C - Sends SIGINT signal to the current foreground job

Files

• headers.h

  • Header files
  • Global variables
  • Function declarations

• main.c

  • main(): Main function to initialise variables and call the loop
  • shell_loop(): Runs the main loop of the code for the continuous execution of the shell

• bgfg.c

  • bg(): Changes a Stopped background job to a Running
  • fg(): Brings a background job to foreground

• background.c

  • background(): Forks the existing process and runs a child process in the background. Once the child terminates, the exit status of the child process prints on the screen.

• foreground.c

  • foreground(): Forks the existing process and runs a child process in the foreground. The parent process resumes once the child terminates and waits till then.

• cd.c

  • cd(): Changes the directory based on absolute or relative path provided

• echo.c

  • echo(): Prints a string argument on the terminal (stdout). Handles cases with and without quotes.

• env.c

  • set(): Changes value of environment variable
  • unset(): Detroys the environment variables

• ls.c

  • ls(): Initialises flags for listing directories specified by absolute or relative path
  • print_ls(): Prints the files in directory according to arguments

• jobs.c

  • print_jobs(): Called when child process dies to print status
  • kjob(): Sends signal val to that process with given job_num
  • overkill(): Kills all background process at once

• pinfo.c

  • pinfo(): Prints the info of the process according to arguments

• piping.c

  • piping():

• pwd.c

  • pwd(): Print the present working directory

• redirection.c

  • redirection(): Allows redirection

• signals.c

  • print_status():
  • ctrlC():

• history.c

  • read_history(): Loads history from previous session.
  • update_history(): Updates history
  • history(): Prints the history according to arguments
  • write_history(): Stores last 20 commands in hist.txt

• history.txt

  • Stores upto 20 used commands