UnixReview.com
June 2006

Listing 1: strftime.c

/* strftime - loadable builtin interface to strftime(3) */

/* See Makefile for compilation details. */

#include <config.h>

#if defined (HAVE_UNISTD_H)
#  include <unistd.h>
#endif

#include "bashtypes.h"
#include "posixtime.h"

#include <stdio.h>

#include "builtins.h"
#include "shell.h"
#include "common.h"
#include "bashgetopt.h"

int
strftime_builtin (list)
     WORD_LIST *list;
{
  char *format, *tbuf;
  size_t tbsize, tsize;
  time_t secs;
  struct tm *t;
  int n;
  intmax_t i;
  int ch;
  char *var = NULL;

  if (list == 0)
    {
      builtin_usage ();
      return (EX_USAGE);
    }

  reset_internal_getopt ();
  while ((ch = internal_getopt (list, "p:")) != -1)
    switch(ch) {
      case 'p':
        var = list_optarg; ## should check for valid variable name
        break;
      default:
        builtin_usage();
        return (EX_USAGE);
    }
  list = loptend;
  if (no_options (list))
      return (EX_USAGE); 

  format = list->word->word;
  if (format == 0 || *format == 0)
    {
      printf ("\n");
      return (EXECUTION_SUCCESS);
    }

  list = list->next;

  if (list && list->word->word)
    {
      n = legal_number (list->word->word, &i);
      if (n == 0 || i < 0 || i != (time_t)i)
	{
	  sh_invalidnum (list->word->word);
	  return (EXECUTION_FAILURE);
	}
      else
        secs = i;
    }
  else
    secs = NOW;

  t = localtime (&secs);

  tbsize = strlen (format) * 4;
  tbuf = 0;

  /* Now try to figure out how big the buffer should really be.  strftime(3)
     will return the number of bytes placed in the buffer unless it's greater
     than MAXSIZE, in which case it returns 0. */
  for (n = 1; n < 4; n++)
    {
      tbuf = xrealloc (tbuf, tbsize * n);
      tsize = strftime (tbuf, tbsize * n, format, t);
      if (tsize)
        break;
    }

  if ( var )
    bind_variable (var, tbuf, 0);
  else
    printf ("%s\n", tbuf);
  free (tbuf);

  return (EXECUTION_SUCCESS);
}

/* An array of strings forming the `long' documentation for a builtin xxx,
   which is printed by `help xxx'.  It must end with a NULL. */
char *strftime_doc[] = {
	"Converts date and time format to a string and displays it on the",
	"standard output.  If the optional second argument is supplied, it",
	"is used as the number of seconds since the epoch to use in the",
	"conversion, otherwise the current time is used.",
        "OPTION: -p VAR - Store the result in shell variable VAR",
	(char *)NULL
};

/* The standard structure describing a builtin command.  bash keeps an array
   of these structures.  The flags must include BUILTIN_ENABLED so the
   builtin can be used. */
struct builtin strftime_struct = {
	"strftime",		/* builtin name */
	strftime_builtin,	/* function implementing the builtin */
	BUILTIN_ENABLED,	/* initial flags for builtin */
	strftime_doc,		/* array of long documentation strings. */
	"strftime [-p VAR] format [seconds]",	/* usage synopsis; becomes short_doc */
	0			/* reserved for internal use */
};