design.txt

Shell: Design document
Purpose
The purpose of this assignment is to design and implement a shell which takes input command from the user, parses it and finally executes it. 

Available Resources
Apart from the standard C libraries, we have used Lex tool to tokenize the user command. The implementation 
of this lex file was given to us along with the initial codes in myshell.c which we have further developed 
to support all the functionalities.

For version control purposes, we have used GIT.

Design
data structures:
	jobSet: 	This structrue stores the head of the list of jobs and the current foreground process.
	job:		Stroes the list of child processes in this particular job. It also maintains some metadata 
				about a job like jobId, number of running processes etc. For eg. a job would be like 
				ls | sort>out.txt
	childProc:	This data structure stores the information about a single child process which is a part of a job.
				For eg. a child process with reference to above example is ls and sort>out.txt
	redirection:This data structure stores about the type of redirection and how to handle it.

void parse(char **ar, jobSet*, job** )

The parse function takes input and creates a job adds it to the linked list, also it create child process and 
sets the command for them and makes everything ready for the run command to execute.

int run(job*,  jobSet*, short isBg)
@param retrun value : returns whether the program returned successfully or not.
This command will run all child processes in a particular job and store their exiting states in the linked 
list and later while retrieving the status a job, we say it completes only when all the child processes 
are completed successfully.

Testing
The testing strategy is to run various combinations of commands and check the output. The shell should 
not crash in any circunstance. Appropriate error messages must be displayed in case of invalid commands.