A C program that implements a simple shell/command-line interpreter. It allows users to execute commands, handle background and foreground processes, handle input/output redirection, and pipe commands together.
compile:
gcc -o simple_shell PA1.c
run:
./simple_shell
ls: List files and directories in the current directory.
pwd: Print the current working directory.
echo Hello, World!: Print the text "Hello, World!".
date: Display the current date and time.
ls > files.txt: Redirect the output of the ls command to a file named files.txt.
cat < files.txt: Redirect the contents of the files.txt file as input to the cat command.
ls | grep txt: List files and pipe the output to grep to search for "txt".
ls | sort: List files and pipe the output to sort to sort the file names.
sleep 5 &: Execute the sleep command in the background for 5 seconds.
ls -R / &: List files and directories in the root directory in the background.
sleep 10: Execute the sleep command for 10 seconds in the foreground. Press Ctrl+Z to stop it and put it in the background.
jobs: Display the list of background jobs.
bg 0: Resume the job at index 0 in the background.
exit: Exit the shell.
The main loop of the shell continuously prompts the user for input, tokenizes the input into a Cmd struct, and then performs various actions based on the input. It supports exiting the shell, displaying job information, resuming stopped jobs, and executing commands in the foreground or background.
Defines global variables and arrays to manage jobs, the current foreground job, the foreground process PID, and the number of jobs.
The program dynamically allocates memory for the Cmd structs representing jobs. It also deallocates this memory at the end of the program.
Cmd to holds information about a command, including the command line, tokenized command, arguments, symbols, process ID, and status flags (done, printed, stopped). It is used to represent each command to be executed.
sigtstpHandler handles the SIGTSTP signal (usually triggered by Ctrl+Z), which suspends the currently running foreground process and adds it to the list of jobs in a stopped state.
Tokenizes a command line input into individual arguments and symbols, storing them in the Cmd struct for later use.
Searches for the index of a specific symbol within the Cmd struct's symbols array.
Handles the execution of a command. It checks for input/output redirection and piping, and if neither is found, it executes the command using the execvp function.
Executes a command in the background by forking a child process and adding it to the list of jobs. The parent process displays the job's information.
Executes a command in the foreground by forking a child process. The parent process waits for the child process to finish before displaying the prompt again.
Checks the status of background jobs. It iterates through the list of jobs, checks if any have terminated, and displays relevant information about them.