OS_Assignment-3

Running the file

• Go to the Assignment folder.
• Execute make on terminal. This complies all the .c files in 'shell' object file.
• Run the program by executing './shell' in the terminal.

Assignment tasks

• This part of the assignment focused on implementing input-output redirection and piping of processes.
• Also implemented signal handling for different types of signals and handling their effects on processes.

Files and their functions:

Assignment-2 added files but some are modified in Assignment-3

headers.h:

• Contains all headers and header files and extern variable declaration.

main.c:

• This file initiates our shell program.
• This file is also used to declare and initialize our extern variables.
• We also keep our SIGNCHLD signal handling in our main function.
• This has the shell loop to continously take user inputs from the terminal.
• Also redirects standard input and output according to input.

prompt.c:

• This file is used to print the username and system name at the start of every command line.
• This also prints our current working directory in every command line.
• This assumes that execution directory of file is root directory.
• Also colors the termial output using ANSI color codes.

parse.c:

• It parses the given argument with given delimiter.

cd.c:

• Implements cd function
• Makes the use of curr_dir, prev_dir and root_dir extern variables to implement previous '-' directory cd command.
• This assumes that execution directory of file is root directory.

pwd.c:

• prints current working directory.

echo.c:

• prints everything written after echo after removing extra white spaces.
• Uses parse.c to remove extra whitespaces.

ls.c:

• Lists the contents and details of the given directory according to flags -a, -l.
• Makes use of getopt() function to parse the input to flags and arguments.
• Uses read_details.c file to print all the details of the contents of the given directory/file according to flags.

read_details.c:

• Uses struct dirent, struct stat to print the details of the contents accoring to the flags.
• Replicates the content shown by bash terminal.

pinfo.c:

• Prints details of the given process id or shell using /proc/[pid]/stat and /proc/[pid]/exe file details.
• Uses fopen in read to access these files.

repeat.c:

• Executes the argument command, about given argument number of times.

history.c:

• Gives the history of the recent executed commands up untill last 20 commands.
• Assumes history reset after each execution of shell.

execute.c:

• Execute System commands using fork and execvp.
• Also handles background processes.
• Also outputs exit status of background process using linked list.
• Also handles signals and input-output redirection for child process.

list.c:

• Implements linked list to store pids and names of running background processes.

handler.c:

• Handler function for *SIGCHLD signal in main function, prints the exit status of our background child process.
• Uses linked list to iterate through process pids and checks exited pids.

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Assignment - 3 added files:

redirect.c:

• Parses the input command to extract input and output files according to symbols '<', '>', '>>'.

piped_command.c

• Handles input commands with piping.
• First parses the command input according to '|' pipe symbol, then uses pipe() and dup2 command to redirect standard input and output for every command execution which is used as input by the next command.

pinfo2.c

• Extract values from /proc/[pid]/stat according to pid.

jobs.c

• Prints all the active background processes with their status and pid.
• Iterates through the list of bg pids and uses pinfo2() to extract status information.

sig.c

• Uses kill() command to send signal according to pid.

fg.c

• Uses kill() command to send SIGCONT to change bg process state from stopped to running and then bring the process to foreground and then wait for it's execution.

bg.c

• Uses kill() command to send SIGCONT to change bg process state from stopped to running but this time keep the process in background.

handler2.c

• Handles SIGTSTP signal to send foreground process to background and change their state to stopped but keeping our shell unaffected.

handler3.c

• Handles *SIGINT signal to kill foreground process but keeping out shell execution unaffected.

replay.c

• This file implements the bonus task which executes a command in intervals over a certain period.
• This was implemented by using forloop for a certain period of input time, and then using sleep function between every iteration we can replicate the periods.