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Write a C program that behaves like a shell which displays the command prompt ‘myshell$’. It accepts the command, tokenize the command line and execute it by creating the child process. Also implement the additional command ‘search’ as myshell$ search f filename pattern : It will search the first occurrence of pattern in the given file myshell$ search a filename pattern : It will search all the occurrence of pattern in the given file myshell$ search c filename pattern : It will count the number of occurrence of pattern in the given 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 search_file(char *filename, char *pattern, char *option) {
    FILE *file = fopen(filename, "r");
    if (file == NULL) {
        perror("fopen");
        return;
    }

    char line[MAX_INPUT_SIZE];
    int count = 0;
    int found = 0;

    while (fgets(line, sizeof(line), file)) {
        if (strstr(line, pattern) != NULL) {
            found = 1;
            count++;
            if (strcmp(option, "f") == 0) {
                printf("Found at line %d: %s", count, line);
                break; // Stop after finding the first occurrence if searching first occurrence
            } else if (strcmp(option, "a") == 0) {
                printf("Found at line %d: %s", count, line);
            }
        }
    }

    fclose(file);

    if (strcmp(option, "c") == 0) {
        printf("Pattern '%s' found %d times in %s\n", pattern, count, filename);
    } else if (!found) {
        printf("Pattern '%s' not found in %s\n", pattern, filename);
    }
}

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 "search" command
        if (arg_count >= 4 && strcmp(args[0], "search") == 0) {
            search_file(args[2], args[3], args[1]);
        } else {
            execute_command(args, arg_count);
        }
    }

    return 0;
}

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