lib/nextelem.c

   1 /* Return the next element of a path.
   2    Copyright (C) 1992 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software
  16    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  17
  18 /* Written by David MacKenzie <djm@gnu.ai.mit.edu>,
  19    inspired by John P. Rouillard <rouilj@cs.umb.edu>.  */
  20
  21 #ifdef HAVE_CONFIG_H
  22 #include <config.h>
  23 #endif
  24
  25 #include <stdio.h>
  26 #if defined(HAVE_STRING_H) || defined(STDC_HEADERS)
  27 #include <string.h>
  28 #else
  29 #include <strings.h>
  30 #ifndef strchr
  31 #define strchr index
  32 #endif
  33 #endif
  34
  35 char *strdup ();
  36 void free ();
  37
  38 /* Return the next element of a colon-separated path.
  39    A null entry in the path is equivalent to "." (the current directory).
  40
  41    If NEW_PATH is non-NULL, set the path and return NULL.
  42    If NEW_PATH is NULL, return the next item in the string, or
  43    return NULL if there are no more elements.  */
  44
  45 char *
  46 next_element (new_path)
  47      char *new_path;
  48 {
  49   static char *path = NULL;     /* Freshly allocated copy of NEW_PATH.  */
  50   static char *end;             /* Start of next element to return.  */
  51   static int final_colon;       /* If zero, path didn't end with a colon.  */
  52   char *start;                  /* Start of path element to return.  */
  53
  54   if (new_path)
  55     {
  56       if (path)
  57         free (path);
  58       end = path = strdup (new_path);
  59       final_colon = 0;
  60       return NULL;
  61     }
  62
  63   if (*end == '\0')
  64     {
  65       if (final_colon)
  66         {
  67           final_colon = 0;
  68           return ".";
  69         }
  70       return NULL;
  71     }
  72
  73   start = end;
  74   final_colon = 1;              /* Maybe there will be one.  */
  75
  76   end = strchr (start, ':');
  77   if (end == start)
  78     {
  79       /* An empty path element.  */
  80       *end++ = '\0';
  81       return ".";
  82     }
  83   else if (end == NULL)
  84     {
  85       /* The last path element.  */
  86       end = strchr (start, '\0');
  87       final_colon = 0;
  88     }
  89   else
  90     *end++ = '\0';
  91
  92   return start;
  93 }
  94
  95 #ifdef TEST
  96 int
  97 main ()
  98 {
  99   char *p;
 100
 101   next_element (getenv ("PATH"));
 102   while (p = next_element (NULL))
 103     puts (p);
 104   exit (0);
 105 }
 106 #endif /* TEST */