SASH

Hey, this is a shell I created!

How to use:

• Clone the directory
• run make inside the directory
• Profit!

Features and Assumption

• MAXLEN = 1024 , which is the maximum length of strings, maximum length of arguments etc

Multiple Commands

• Use ; to use multiple commands in the same line!

• How does it work? sash uses a tokenizer to split the command line arguments based on ;

• One can also use | to pipe commands like ls -al | wc, where the output of ls -al becomes input of wc. This was done using an iterative function and C's pipe() command

• You can also use >, < or >> for redirecting input manually, and this can also be used with piping.

cd

• Change the directory to place mentioned by using cd
• `~ . .. -~ can be used just as you would in a normal shell
• A very simple and effecient implementation where sash gets the relative path from current dir to required, and then changes directory.

pwd

• Get path to the current working directory by using pwd
• Simply gets the absolute path of current working directory, then converts it into relative based on home

echo

• Print everything which follows the command echo

pinfo

• Print the information for a given Process ID using pid
• Gives information about:
  • Proccess ID
  • Process Status
  • Virtual Memory
  • Executable Path
• Reads extra information from proc files and displays it accordingly.

jobs

• Prints all the background processes which arent terminated yet jobs.
• -r flag only prints running jobs, and -s flag only prints stopped jobs
• To implement this, sash stores a array of structs with all the background jobs in it. It also works in conjuction with CTRL+Z.

sig

• Sends a signal given index (of process in job list) and signal to send.
• Sash uses kill to implement this function

bg

• Brings a stopped background process back to life!! (still in background tho)
• A signal is sent to the process to achieve this

replay

• A very simple command replay -command echo hi -interval 3 -period 6 where command echo hi is executed every 3 seconds till 6 second pass.
• This was done using C's <time.h> module and sleep() function

Signal Handling

• Basing signal handling is implemented to keep sash as close to normal bash, where CTRL+ terminates a foreground process, CTRL+Z stopps a foreground process and takes it to background and CTRL+D exits the shell

Directory Structure

• The main loop is within sash.c, which also intialises constants like home and sets up signal
• Then command goes to command.c which parses the input string, and redirects it accordingly
• In each loop, we run info.c to print the prompt
• cd.c contains code related to cd
• ls.c contains code related to ls
• pinfo.c contains code related to pinfo
• pwd.c contains code related to pwd
• print.c contains code related to echo
• signal.c handles reaping the background child processes, also does signal handling
• ground.c contains code related to bg
• jobs.c prints a list of jobs and contains code for it
• pipe.c is the first step of command parsing, which then goes to redirect.c
• redirect.c is the second part of command parsing which then goes to command.c
• replay.c is used to handle the command replay. It calls pipe.c to execute the said command
• sig.c is code related to sig function
• utilities.c contains some functions which are used everywhere
• header.h contains some headers and function definitions