Where can I find the program that runs the -wc command?

UNIX for Beginners Q & A
1

Hey guys, I was wondering. When I enter a command in the terminal -wcl for a word count, where is that program located in the kernel?

2

wc is not located in the kernel.

wc and similar shell builtins and other similar programs run in the shell, not the kernel.

3

Ah I see so where might I go to look at the code itself, any idea? Would it even be possible?

4

Hi Neo...

More to the point why is the OP interested in entering kernel space, (ring 0), at all?

@Circuits:
If you are running Linux you have two methods /dev/<device> for _direct_, (term used loosely), HW access and 'int 80' for assembly code...
Linux System Call Table

5

You mean the code for wc ?

The start to the answer for that question depends on the operation system you are using / interested in.

6

Yes wc, I am using Ubuntu 18.04.

7

For Ubuntu, you can read the source code directly yourself.

For example, you can pull it down and search it using, like so:

apt-get source linux-source-3.2.0

or, you can go to the Ubuntu archive here:

http://archive.ubuntu.com/ubuntu/

Enjoy!

1 Like
8

Also, FYI, you can easily find various versions of the free and open source code for wc on the net.

Here is an example:

Appendix A Source of the wc command

The source file wc.c ... (one of many examples on the net)

/* Sample implementation of wc utility. */

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

typedef unsigned long count_t;  /* Counter type */

/* Current file counters: chars, words, lines */
count_t ccount;
count_t wcount;
count_t lcount;

/* Totals counters: chars, words, lines */
count_t total_ccount = 0;
count_t total_wcount = 0;
count_t total_lcount = 0;

/* Print error message and exit with error status. If PERR is not 0,
   display current errno status. */
static void
error_print (int perr, char *fmt, va_list ap)
{
  vfprintf (stderr, fmt, ap);
  if (perr)
    perror (" ");
  else
    fprintf (stderr, "\n");
  exit (1);  
}

/* Print error message and exit with error status. */
static void
errf (char *fmt, ...)
{
  va_list ap;
  
  va_start (ap, fmt);
  error_print (0, fmt, ap);
  va_end (ap);
}

/* Print error message followed by errno status and exit
   with error code. */
static void
perrf (char *fmt, ...)
{
  va_list ap;
  
  va_start (ap, fmt);
  error_print (1, fmt, ap);
  va_end (ap);
}

/* Output counters for given file */
void
report (char *file, count_t ccount, count_t wcount, count_t lcount)
{
  printf ("%6lu %6lu %6lu %s\n", lcount, wcount, ccount, file);
}

/* Return true if C is a valid word constituent */
static int
isword (unsigned char c)
{
  return isalpha (c);
}

/* Increase character and, if necessary, line counters */
#define COUNT(c)       \
      ccount++;        \
      if ((c) == '\n') \
        lcount++;

/* Get next word from the input stream. Return 0 on end
   of file or error condition. Return 1 otherwise. */
int
getword (FILE *fp)
{
  int c;
  int word = 0;
  
  if (feof (fp))
    return 0;
      
  while ((c = getc (fp)) != EOF)
    {
      if (isword (c))
        {
          wcount++;
          break;
        }
      COUNT (c);
    }

  for (; c != EOF; c = getc (fp))
    {
      COUNT (c);
      if (!isword (c))
        break;
    }

  return c != EOF;
}
      
/* Process file FILE. */
void
counter (char *file)
{
  FILE *fp = fopen (file, "r");
  
  if (!fp)
    perrf ("cannot open file `%s'", file);

  ccount = wcount = lcount = 0;
  while (getword (fp))
    ;
  fclose (fp);

  report (file, ccount, wcount, lcount);
  total_ccount += ccount;
  total_wcount += wcount;
  total_lcount += lcount;
}
  
int
main (int argc, char **argv)
{
  int i;
  
  if (argc < 2)
    errf ("usage: wc FILE [FILE...]");
  
  for (i = 1; i < argc; i++)
    counter (argv);
  
  if (argc > 2)
    report ("total", total_ccount, total_wcount, total_lcount);
  return 0;
}