Write a C program that behaves like a shell which displays the command prompt ‘myshell$’. It accepts the command, tokenize the command line and execute it by creating the child process. Also implement the additional command ‘typeline’ as myshell$ typeline n filename: It will display first n lines of the file. myshell$ typeline -n filename: It will display last n lines of the file. myshell$ typeline a filename: It will display all the lines of the file.

 #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>

#define MAX_INPUT_SIZE 1024
#define MAX_ARGS 10

void execute_command(char *args[], int count) {
    pid_t pid = fork();
    if (pid == -1) {
        perror("fork failed");
        exit(EXIT_FAILURE);
    } else if (pid == 0) {
        // Child process
        execvp(args[0], args);
        perror("execvp failed");
        exit(EXIT_FAILURE);
    } else {
        // Parent process
        wait(NULL); // Wait for the child to complete
    }
}

void typeline(char *option, char *filename) {
    FILE *file = fopen(filename, "r");
    if (file == NULL) {
        perror("fopen");
        return;
    }

    char line[MAX_INPUT_SIZE];
    int n = 0;
    int line_count = 0;

    if (option[0] == '-') {
        // Display last n lines
        n = atoi(option + 1);
        if (n <= 0) {
            fclose(file);
            return;
        }

        fseek(file, 0, SEEK_END);
        long file_size = ftell(file);

        while (file_size > 0 && line_count < n) {
            fseek(file, --file_size, SEEK_SET);
            if (fgetc(file) == '\n') {
                line_count++;
            }
        }
    } else if (strcmp(option, "a") == 0) {
        // Display all lines
    } else {
        // Display first n lines
        n = atoi(option);
        if (n <= 0) {
            fclose(file);
            return;
        }
    }

    line_count = 0;
    while (fgets(line, sizeof(line), file)) {
        printf("%s", line);
        line_count++;
        if (n > 0 && line_count >= n) {
            break;
        }
    }

    fclose(file);
}

int main() {
    char input[MAX_INPUT_SIZE];
    char *args[MAX_ARGS];
    int arg_count;

    while (1) {
        printf("myshell$ ");
        if (fgets(input, sizeof(input), stdin) == NULL) {
            break; // Exit the loop on EOF
        }

        input[strcspn(input, "\n")] = 0; // Remove the newline character

        // Tokenize the input
        arg_count = 0;
        char *token = strtok(input, " ");
        while (token != NULL) {
            args[arg_count] = token;
            arg_count++;
            token = strtok(NULL, " ");
        }
        args[arg_count] = NULL; // Null-terminate the argument list

        // Handle the "typeline" command
        if (arg_count >= 3 && strcmp(args[0], "typeline") == 0) {
            typeline(args[1], args[2]);
        } else {
            execute_command(args, arg_count);
        }
    }

    return 0;
}

ALL CLEAR PRACTICAL

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