Linux Shell in C

Introduction

A custom made user-defined interactive shell program with implementations of some built in commands and the capability to start any user defined executable. Created as part of CS3.301 - Operating Systems and Networks at IIIT-H. Problem statements present in the two .pdf files.

To compile and run the shell

• Clone this directory and cd into it.
• Run the command make.
• Run ./srujshell to get a prompt of the form username@system_name:curr_dir
• Run any command in the shell. It can entail as many number of tabs and spaces, the shell accounts for those.
• In order to exit, you can run either exit or quit.

Implemented features

Built-in commands

1. pwd

   • Displays the name of current working directory.

2. cd [directory]

   • Changes current working directory to the directory specified.

3. echo [argument]

   • Displays whatever is specified in [argument]

4. ls

   • Lists all the files and directories in the specified directory.
   • Variations such as ls, ls . , ls etc also work.
   • Also handles multiple directories as arguments. eg. ls -l dir1 dir2 dir3
   • Also highlights directories in blue and executable files in green.

5. pinfo [pid]

   • Displays process info such as status, memory and executable path about given pid. If no pid is mentioned, displays information of the shell.

6. discover <target_dir> <type_flags> <file_name>

   • Searches for files in a directory hierarchy.

7. jobs

   • Prints a list of all currently running jobs along with their PID in order of their creation and also their status.
   • Gives the state of the job – Running, Sleeping, Stopped or Defunct.

8. sig <jobnumber> <signalnumber>

   • Takes the job number (assigned by your shell) of a running job and sends the signal corresponding to the signal number to that process.

9. fg <jobNumber>

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

10. bg <jobNumber>

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

11. history

    • Prints the last 10 commands if no argument specified.

Background and foreground processes

• Shell supports '&' operator which lets a program run in background.
• All other commands are treated as system commands like emacs, vim etc.
• Upon termination of a background process, the shell prints its PID and exit status.

Additional features

1. CTRL-Z

   • Pushes any currently running foreground job into the background, and change its state from ‘running’ to ‘stopped.

2. CTRL-C

   • Interrupts any currently running foreground job, by sending it the SIGINT signal.

3. CTRL-D

   • Logs you out of the shell.

4. Autocompletion

   • Autocompletes the file name on pressing the tab key.