A-Shell: A Custom Shell in C

Requirements

• Linux OS
• GCC Compiler

How to Run

To run A-Shell,

• Open terminal in the root directory and run make
• run ./shell to start the shell.

Functionality and Files

Features

• Basic commands cd, pwd, echo, ls, history, discover are supported

Basic Functionality

• Input handled for all commands in main.c, input.c and execute.c
• Displaying of prompt handled in prompt.c, main.c
• File redirection supported using >, >> and < tokens.
• Autocomplete functionality, detects and autocompletes the name of currently typed file or directory.
• Signal handling :
  • CTRL + Z sends the currently running foreground job to background and changes its state from running to stopped. Has no effect if no foreground job running.
  • CTRL + C interrupts the currently running foreground job by sending the SIGINT signal. Has no effect if there is no foreground job running.
  • CTRL + D logs the user out of the shell without having any effect on the actual terminal.
• Piping functionality for commands.

Commands

cd

• Implemented in cd.c

echo

• Print the arguments passed to echo in a space seperated manner
• Implemented in execute.c

pwd

• Print the present working directory
• Implemented in execute.c

ls

• Print the contents of the specified directories (current directory if argument list empty)
• Supports -l and -a flags.
• Implemented in ls.c

system commands

• Shell executes system in either background or foreground
• Commands invoked with & run in the background while all other commands run in the foreground.
• Main functionality in bg_handler.c with supplementary code in execute.c, input.c and process_list.c

pinfo

• Prints the process related info of your shell program
• Implemented in pinfo.c

discover

• Searches for the target file/directory in the directory given as argument (current directory by default) according to the given flags. (-d searches for directories only while -f searches for files only)
• Implemented in discover.c

history

Displays a maximum of latest 10 commands input to the shell accross all instances of the shell created on the system. Following are the basic implementation details:

• Main implementation in history.c
• init_shell() is called in main to ensure existence of the file /tmp/A-Shell_history.txt whenever a shell instance is created
• Updation of /tmp/A-Shell_history.txt on every input is handled in input.c

jobs

Displays a list of currently existing background processes with their index, status (running or stopped) and name sorted in alphabetical order.

• Main implementation in jobs.c

sig

Sends the specified signal to the specified job index as shown in jobs.

• Main implementation in jobs.c

fg

Brings the specified job index, a currently background job, to the foreground and changes its state to running.

• Main implementation in jobs.c

bg

Changes the state of a stopped background process to running in the background. It does nothing if the background job is already running.

• Main implementation in jobs.c