Sa3eedoo/Simple-shell-implementation

It is required to implement a Unix shell program. Your shell must support the following: 1. The internal shell command "exit" which terminates the shell Concepts: shell commands, exiting the shell. System calls: exit() 2. A command with no arguments Example: ls …etc Details: Your shell must block until the command completes and, if the return code is abnormal, print out a message to that effect. Concepts: Forking a child process, waiting for it to complete and synchronous execution. System calls: fork() , execvp() , exit() , wait() 3. A command with arguments Example: ls –l, cp source destination, rm filename. Details: Argument 0 is the name of the command. Concepts: Command-line parameters 4. A command, with or without arguments, executed in the background using &. Example: firefox & Details: In this case, your shell must execute the command and return immediately, not blocking until the command finishes. Concepts: Background execution, signals, signal handlers, processes and asynchronous execution. Assignment 1 - Simple shell implementation 2 Requirements: You have to show that the opened process will be nested as a child process to the shell program via opening the task manager found in the operating system like in following figure. Additionally you have to write in a log file when a child process is terminated (main application will be interrupted by a SIGCHLD signal). So you have to implement an interrupt handler to handle this interrupt and do the corresponding action to it.To process the user command, do the following: 1. Your command shell should take the user command and its parameter(s), i.e., “ls” and “–l” in this example, and convert them into C strings. (Recall that a C string terminates with a null string, i.e., \0.) 2. The command shell should create a child process via fork() . Assignment 1 - Simple shell implementation 3 3. The child process passes the C strings—the command and parameter(s)—to execvp() . 4. The parent process, i.e., the command shell, should wait, via wait() , for the child process to finish. 5. The command shell gets the next command and repeats the above steps. The command shell terminates itself when the user types exit. In case a user wants to execute the command in background (i.e. as a background process), he/she writes & at the end of the command. For example, a user command can be: Shell > firefox & In this case, your command shell should not wait for the child by skipping the Step 4. You should keep a log file for your shell program such that whenever a child process terminates, the shell program appends the line “Child process was terminated” to the log file. To do this, you have to write a signal handler that appends the line to the log file when the SIGCHLD signal is received.