Socket programming in C

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netinet/in.h>
#include <string.h>
#include <signal.h>
#include <time.h>
#include <sys/select.h>
#include <sys/fcntl.h>
#include <sys/time.h>

#define BACKLOG 3

void error(const char *ptr);
/*Global Variables*/
int sockfd = 0, newsockfd = 0;
int ret = 0;
void call(char *ptr)
{
    FILE *fp;
    char arr[100] = {'\0'};
    fp = popen(ptr, "r");
    while (1)
    {
        fread(arr, sizeof(arr), 1, fp);
        write(newsockfd, arr, sizeof(arr));
        if (feof(fp) == 1)
        {
            sleep(1); //used to change priority
                      /*If i am not using sleep() than the client goes into blocking and waiting for server*/
            write(newsockfd, "quit", sizeof("quit"));
            break;
        }
    }
    pclose(fp);
}

void _close()
{
    printf("closing the connection");
    ret = close(newsockfd);
    if (ret < 0)
        error("close");
    ret = close(sockfd);
    if (ret < 0)
        error("close");
    exit(0);
}

void handler(int _catch)
{
    printf("received signal of %d\n", _catch);
    _close();
}

int main(int argc, char *argv[])
{
    int port = 0;
    int socklen = 0;
    int i = 0, j = 0;
    int ret1 = 0;
    char buff[255];
    char cmp_str[] = {"quit"};
    char string[100] = {"\0"};
    char *retptr = NULL;
    struct sockaddr_in server_addr, client_addr;
    clock_t start, end;
    if (argc < 2)
    {
        printf("Please give the port address\n");
        exit(1);
    }
    socklen = sizeof(client_addr);

    /*Taking port address*/
    port = atoi(argv[1]);

    /**Creating a socket**/
    sockfd = socket(PF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("socket");

    /** sockaddr**/
    server_addr.sin_family = AF_INET;                /* Internet address family for IPv4*/
    server_addr.sin_addr.s_addr = (htonl)INADDR_ANY; /*Any incoming interface*/
    server_addr.sin_port = htons(port);              /*Local port*/

    /**Bind the socket**/
    ret = bind(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr));
    if (ret < 0)
        error("bind");

    /**listen**/
    ret = listen(sockfd, BACKLOG);
    if (ret < 0)
        error("listen");

    /**accept function**/
    newsockfd = accept(sockfd, (struct sockaddr *)&client_addr, &socklen);
    if (newsockfd < 0)
        error("accept");

    /*Signal Handling*/
    signal(SIGINT, handler);

    /*Communication*/
    fcntl(newsockfd, F_SETFL, O_NONBLOCK); // set to non-blocking
    fcntl(newsockfd, F_SETFL, O_ASYNC);    // set to asynchronous I/O

    system("clear");

    /*read*/
    bzero(buff, sizeof(buff));

    ret = read(newsockfd, (void *)buff, sizeof(buff));
    /*ret1 = select(BACKLOG, &readfds, NULL, NULL, &timeout);
    if (ret == 0)
    {
        printf("time out\n");
        _close();
    }*/
    if (ret < 0)
        perror("read");
    printf("Client :- %s", buff);

    call("ls | grep txt");

    /*Read the query*/
    bzero(buff, sizeof(buff));
    int opt = 3;
    setsockopt(newsockfd, SOL_SOCKET, SO_RCVLOWAT, &opt, sizeof(opt));

    /*For Time out connection*/
    fd_set readfds;
    FD_ZERO(&readfds);
    FD_SET(0, &readfds);
    struct timeval timeout;
    timeout.tv_sec = 10; //seconds//
    timeout.tv_usec = 0; //micro seconds//

    ret=select(1, &readfds, NULL, NULL, &timeout);
    if (ret==0)
    {
        printf("time out\n");
        _close();
    }
    else if(ret>0)
    {
        ret = read(newsockfd, (void *)buff, sizeof(buff));
        if (ret < 0)
            perror("read");
        if (ret1 == 0)
        {
            printf("time out\n");
            _close();
        }
        printf("Client :- %s", buff);

        /*transfering the file*/
        strncpy(string, "cat", strlen("cat"));
        for (i = 0; string[i] != '\0'; i++)
            ;
        string[i] = ' ';
        i++;
        for (i, j = 0; buff[j] != '\0'; j++, i++)
        {
            string[i] = buff[j];
        }
        call(string);
        _close();
    }
}
void error(const char *ptr)
{
    perror(ptr);
    exit(1);
}