CLI (Command Line Interperator)

Can any1 please help me in CLI

I am having trouble in writing this program.

The program repeatedly accepts a "command line" from its standard input and executes it.

More than one command line can be executed per invocation of the program.

I am trying to "exec" the command line from
within a child process of my program.

P.S. I am running it on unix

As, I am new to programming. any help would be much appreciated.

First you tell one thing,

You want to execute only commands of the shell? or You want to create your own commands ?

you want to start writing the structure of the CLI on a pattern like this one. Then it's all easy.

Code:

---


#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>

#define SIZE 255
/*#define DEBUG*/

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

  char inputLine[ SIZE ];
  int  pid;

  while( 1 ) {

      if ( fgets( inputLine, SIZE-1, stdin ) == NULL ) {
        fprintf( stderr, "fgets error.\n");
        exit(1);
      }

      inputLine[ strlen(inputLine)-1 ] = 0; /* remove \n */

#ifdef DEBUG
      /* some debug informations */
      fprintf( stdout, "read cmd line: %s\n", inputLine );
#endif

      if ( strcasecmp( inputLine, "exit" ) == 0 ) {
        /* by typing "exit", the users exits */
        fprintf( stdout, "exiting\n");
        break;
      }

      /* fork to exec the command line */

      if ( (pid =  fork()) < 0 ) {
        fprintf( stderr, "fork error, errno = %d\n", errno );
      } else if ( pid == 0 ) {

#ifdef DEBUG
        fprintf( stdout, "child %d will execute %s\n", getpid(), inputLine );
#endif
        system( inputLine );
        exit(0);
      } else {

#ifdef DEBUG
        fprintf( stdout, "parent started child %d\n", pid);
#endif

      }

  }

  fprintf( stdout, "bye bye..\n");
  return 0;
}

---

that's just one simple example. All the command are executed in the background, due to the fork.

Yes quark,

I need to implement that and execute commands of the shell.

and the second part is to create your own commands