qshell.c

/* qshell.c
 *
 *    Writing a shell in C
 *    C. Vickery
 *
 *        First step: Recognize and interpret built-in commands.
 */
#include 
#include 
#include 
#include 

/*  New Types
 *  -------------------------------------------------------------------
 */
typedef enum { false, true } bool;

typedef int procfun( char * );


/*  Built-in commands
 *  -------------------------------------------------------------------
 */
int terminate( char *code ) {

  exit( code ? atoi(code) : 0 );
  
  }

/*  Dispatch Table for built-in commands
 *  -------------------------------------------------------------------
 */
typedef struct {
  char      *name;
  procfun   *do_builtin;
  } dt;

dt builtins[] = { { "exit", terminate },
                };

const int numBuiltins = sizeof builtins / sizeof builtins[0];

/*  Shell Variables
 *  -------------------------------------------------------------------
 */
 
char      *PS1 = "q! ";
int       cmd_status;


/*  Function main()
 *  -------------------------------------------------------------------
 *
 *      Reads command lines and executes built-ins.
 */
int
main( int argc, char *argv[], char *envp[] ) {

char    inBuf[1024],
       *cmd_name;
int     i;
bool    found;

  for ( ;; ) {
  
    printf( "%s", PS1 );
    gets( inBuf );
    cmd_name = strtok( inBuf, "\t\n " );

    if (cmd_name) {

      found = false;
      for ( i = 0; i < numBuiltins; i++ ) {

          if ( !strcmp( cmd_name, builtins[i].name ) ) {
            cmd_status = builtins[i].do_builtin(
                                      strtok( NULL, "\t\n " ) );
            found = true;
            break;

          }

        }
        
      if ( !found ) {
        printf( "%s: %s: unrecognized command\n", argv[0], cmd_name );
        }
        
      }
      
    }
  
  return 0;

  }