Creating your own "cat" command

In this blog post I am going to explain how to create your own cat command :-) . we can do it with a simple 'C' program with command line arguments. We write a simple program with basic file operations and command line arguments.


Step 1: Open your favorite text editor
Step 2: Copy the following code to your text editor

/*
 @
 @ File Name   : mycat.c
 @ Author      : Prabhendu V Senan
 @ Description : This is a simple C program to display the contents of a file(exactly like the "cat" command in Linux)
 @                                                                          
 @
 */

#include
#include

#define INVALID_ARG_LIST 2


int main(int argc,char *argv[])
{

   FILE *pfile     = NULL;
   char *file_name = NULL;
   int fchars      = 0;
   int arg_index   = 0;

   /* If no file name is given then exit the program  */
   if(argc < INVALID_ARG_LIST)
   {
     printf("Correct usage is: mycat \n");
     exit(1);
   }

   for(arg_index = 1; arg_index < argc; arg_index++)
   {
 
   file_name = argv[arg_index];

   /* Try to open the file. If failed,Exit the program */
   if(!(pfile = fopen(file_name,"r")))
   {
     printf("Unable to open file!!\nEither the file doesn't exist or pemission denied\n");
     exit(1);
   }

   while((fchars = fgetc(pfile)) != EOF)
   {
       putchar(fchars);
   }
  
      fclose(pfile);

      pfile     = NULL;
      file_name = NULL;
      fchars    = 0;
   }
 
   return 0;
}

Step 3: Save the file(ex: mycat.c)
Step 4: Go to file location
            Example: cd /home/senan/myprograms
Step 5: Compile the file 
            cc -o mycat mycat.c in your terminal
Step 6: run the program by
            ./mycat /etc/passwd or you can copy the file to /bin in order to avoid the ./ usage. That is 
            sudo cp mycat /bin
Step 7: :-)