Developing A Linux-Like Command Shell With C Language ✓ Solved

Developing a Linux Like Command Shell With Cc Languageyour Implemen

Developing a Linux-like command shell with C/C++ language your implementation of the "builtin commands": a. cd - Change the current default directory to . If the argument is not present, report the current directory. If the directory does not exist an appropriate error should be reported. This command should also change the PWD environment variable. b. clr - Clear the screen. c. dir - List the contents of directory . d. environ - List all the environment strings. e. echo - Display on the display followed by a new line (multiple spaces/tabs may be reduced to a single space). f. help - Display the user manual using the more filter. g. pause - Pause operation of the shell until 'Enter' is pressed. h. quit - Quit the shell. i. The shell environment should contain shell= /myshell where /myshell is the full path for the shell executable(not a hardwired path back to your directory, but the one from which it was executed).

Sample Paper For Above instruction

Developing a Linux Like Command Shell With Cc Languageyour Implemen

This paper presents a comprehensive approach to developing a Linux-like command shell utilizing C/C++ programming languages. The focus is on implementing core "builtin commands" that enable users to interact with the operating system in a manner similar to standard Linux shells. These commands include 'cd', 'clr', 'dir', 'environ', 'echo', 'help', 'pause', and 'quit', each fulfilling specific functionalities.

Introduction

Shells play a vital role in operating system interfaces by allowing users to execute commands and manage system resources efficiently. Developing a custom shell in C/C++ offers educational insights into process management, command parsing, environment variables, and user interaction. This implementation aims to mimic Linux shell behavior, focusing on essential built-in commands that enhance user control and system navigation.

Implementation of Built-in Commands

1. cd (Change Directory)

The 'cd' command changes the current working directory. If no argument is provided, it reports the current directory. If the specified directory does not exist, it will display an error message. Additionally, it updates the 'PWD' environment variable to reflect the change.

void changeDirectory(const char *path) {
if (path == NULL) {
char cwd[1024];
if (getcwd(cwd, sizeof(cwd)) != NULL) {
printf("%s\n", cwd);
} else {
perror("Error retrieving current directory");
}
} else {
if (chdir(path) == 0) {
setenv("PWD", getcwd(NULL, 0), 1);
} else {
perror("Error changing directory");
}
}
}

2. clr (Clear Screen)

The 'clr' command clears the terminal screen using system calls, typically by invoking the 'clear' command available in Unix/Linux systems.

void clearScreen() {
system("clear");
}

3. dir (List Directory Contents)

The 'dir' command lists contents of the current directory or a specified directory, similar to the 'ls' command.

void listDirectory(const char *path) {
DIR *dir;
struct dirent *entry;
if (path == NULL) {
path = ".";
}
dir = opendir(path);
if (dir == NULL) {
perror("Unable to open directory");
return;
}
while ((entry = readdir(dir)) != NULL) {
printf("%s\n", entry->d_name);
}
closedir(dir);
}

4. environ (Display Environment Variables)

This command enumerates all environment strings available to the process.

void listEnvironment() {
extern char **environ;
for (int i = 0; environ[i] != NULL; i++) {
printf("%s\n", environ[i]);
}
}

5. echo (Display Message)

The 'echo' command prints its arguments to the terminal, reducing multiple spaces or tabs to a single space and appending a newline at the end.

void echoMessage(char *args[]) {
int i = 1; // skipping the command itself
while (args[i] != NULL) {
printf("%s ", args[i]);
i++;
}
printf("\n");
}

6. help (Display User Manual)

The 'help' command displays documentation or manual information, using the 'more' command to filter output for better readability.

void displayHelp() {
system("man -k 'your_shell_name' | more");
}

7. pause (Pause Execution)

The 'pause' command halts the shell until the user presses the 'Enter' key.

void pauseShell() {
printf("Press Enter to continue...");
while (getchar() != '\n');
}

8. quit (Exit Shell)

Terminating the shell process cleanly.

void quitShell() {
exit(0);
}

Shell Environment Configuration

The shell environment must include a variable 'shell' that contains the full path of the executable, dynamically determined at runtime to avoid hardcoded paths.

void setShellPath() {
char path[1024];
ssize_t count = readlink("/proc/self/exe", path, sizeof(path) - 1);
if (count != -1) {
path[count] = '\0';
setenv("shell", path, 1);
}
}

Conclusion

Implementing a custom Linux-like shell in C/C++ involves detailed handling of process creation, command parsing, environment management, and user interaction. The above commands cover core functionalities that enable effective system navigation and management akin to standard shells. Further enhancements may include command history, scripting capabilities, and advanced process control for a more robust shell environment.

References

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