Overview

An interactive shell written in C with foreground/background process, redirection and piping support.

Execution:

makefile
./a.out

Supported Commands

cd < . / .. / ~ / - / directoryName / directoryPath >
ls < . / .. / -l / -a / -la / -al >
echo
pinfo (argument optional)
fg
bg
history (argument optional)
nightswatch -n [time interval] interrupt
setenv var [value]
unsetenv var
jobs
kjob
overkill
quit

Signal Handling

CTRL+Z : It pushes any currently running foreground job into the background and changes its state from running to stopped.

CTRL+C : It interrupts any currently running foreground job, by sending it the ​SIGINT​ signal.

CTRL+D : performs same function as quit command.

Description of files:

makefile:

creates executable file.

header.h:

contains all the header files, global variables and functions definitions used in the program.

cd.c:

contains code to execute function of "cd" command. I used "chdir" command to get the directory address. Appropriate error message is displayed if directory is not present.

check_bg.c:

contains code to check if any background process has ended normally or abnormally.

echo.c:

contains code to execute function of "echo" command. Extra spaces and tabs are trimmed.

###exec_comms.c: matches the command to be execute and then calls the appropriate function with required parameters.

fgbg.c:

contains code that handles background and foreground processes. Can be used to send foreground process to background and vice-versa and change the status of any process from running to stopped and vice versa.

history.c:

contains code to execute function of "history" command. Two functions- one to add to history_log.txt file and another to print from history_log.txt file. Handled cases if argument is > 20.

job.c:

contains code to list all the currently running background processes.

kjob.c:

contains code to kill a specific process, specified by its Jobid.

ls.c:

contains code to execute function of "ls" command. Used functions like opendir(directory_address), readdir(directory_address), stat(parameters), getpwuid(parameters), getgrgid(parameters), ctime(parameters).

nightswatch.c:

contains code to execute function which print the number of times the CPU(s) have been interrupted by keyboard controller. A line is printed every x seconds as input by user and the program is stopped if 'q' is pressed. Tokens 1 and 3 are printed from the proc/interrupt file since token 1 is CPU core number and token 3 is the value.

others.c:

contains code to execute commands other than the ones mentioned in assignment.

overkill.c:

contains code to kill all background processes.

pinfo.c

contains code to print the pid of the process. Used function getpid() to get the pid and printed details of the process. Used syntax proc/[pid]/exec, proc/[pid]/stat, proc/[pid]/statm.

pipe.c:

contains code to handle the piping of commands.

prompt.c:

contains code to print the prompt of the shell. Prints in format: <username@hostname:directory_name>

read_input.c:

contains code to accept input from the shell and execute the function accordingly. Reads line from terminal and breaks it down into tokens using ";" as delimiter by function strtok().

redirect.c:

contains code to handle the redirection of commands.

setenv.c:

contains code to set environment variables.

unsetenv.c:

contains code to unset environment variables.

shell.c:

contains the skeleton code of the shell. The shell runs till we get the command to quit.