C program to find pid of a file

include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
    int process_id;
    char process_id_from_file[10];
    FILE *pid_fd;
    char command[100];

    sprintf(command,"pidof %s", argv[1]);
    pid_fd = popen(command, "r");
    if (pid_fd == NULL)
    {
       // perror("Error in reading pgrep %s", process_name);
        perror("Error in reading pgrep ");
        return -1;
    }

    if (fgets(process_id_from_file, sizeof process_id_from_file , pid_fd) == NULL)
    {
        return -1;
    }
    pclose(pid_fd);

    process_id = atoi(process_id_from_file);

    if (process_id != 0)
    {
        printf("\nprocess id : %d \n", process_id);
    }
   return 0;
}