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   1 /****************************************************************/
   2 /*                                                              */
   3 /*      putenv(3)                                               */
   4 /*                                                              */
   5 /*              Change or add an environment entry              */
   6 /*                                                              */
   7 /****************************************************************/
   8 /*   origination        1987-Oct-7               T. Holm        */
   9 /****************************************************************/
  10
  11 /*
  12 Path: hoptoad!pacbell!ames!ll-xn!mit-eddie!uw-beaver!ssc-vax!uvicctr!tholm
  13 From: tholm@uvicctr.UUCP (Terrence W. Holm)
  14 Newsgroups: comp.os.minix
  15 Subject: putenv(3)
  16 Message-ID: <395@uvicctr.UUCP>
  17 Date: 5 May 88 06:40:52 GMT
  18 Organization: University of Victoria, Victoria B.C. Canada
  19
  20 EFTH Minix report #2  - May 1988 -  putenv(3)
  21
  22 This is an implementation of putenv(3) that we
  23 wrote for Minix. Please consider this a public
  24 domain program.
  25 */
  26
  27 #define NULL 0
  28 #define  PSIZE  sizeof(char *)
  29
  30 extern  char  **environ;
  31
  32 char  *strchr();
  33 char  *malloc();
  34
  35 /****************************************************************/
  36 /*                                                              */
  37 /*      int                                                     */
  38 /*      putenv( entry )                                         */
  39 /*                                                              */
  40 /*              The "entry" should follow the form              */
  41 /*              "NAME=VALUE". This routine will search the      */
  42 /*              user environment for "NAME" and replace its     */
  43 /*              value with "VALUE".                             */
  44 /*                                                              */
  45 /*              Note that "entry" is not copied, it is used     */
  46 /*              as the environment entry. This means that it    */
  47 /*              must not be unallocated or otherwise modifed    */
  48 /*              by the caller, unless it is replaced by a       */
  49 /*              subsequent putenv().                            */
  50 /*                                                              */
  51 /*              If the name is not found in the environment,    */
  52 /*              then a new vector of pointers is allocated,     */
  53 /*              "entry" is put at the end and the global        */
  54 /*              variable "environ" is updated.                  */
  55 /*                                                              */
  56 /*              This function normally returns 0, but -1        */
  57 /*              is returned if it can not allocate enough       */
  58 /*              space using malloc(3), or "entry" does not      */
  59 /*              contain a '='.                                  */
  60 /*                                                              */
  61 /****************************************************************/
  62
  63
  64 int
  65 putenv( entry )
  66   char *entry;
  67 {
  68   unsigned length;
  69   unsigned size;
  70   char     *temp;
  71   char     **p;
  72   char     **new_environ;
  73
  74   /*  Find the length of the "NAME="  */
  75
  76   temp = strchr(entry,'=');
  77   if ( temp == 0 )
  78     return( -1 );
  79
  80   length = (unsigned) (temp - entry + 1);
  81
  82
  83   /*  Scan through the environment looking for "NAME="  */
  84
  85   for ( p=environ; *p != 0 ; p++ )
  86     if ( strncmp( entry, *p, length ) == 0 )
  87       {
  88       *p = entry;
  89       return( 0 );
  90       }
  91
  92
  93   /*  The name was not found, build a bigger environment  */
  94
  95   size = p - environ;
  96
  97   new_environ = (char **) malloc( (size+2)*PSIZE );
  98
  99   if ( new_environ == (char **) NULL )
 100     return( -1 );
 101
 102   memcpy ((char *) new_environ, (char *) environ, size*PSIZE );
 103
 104   new_environ[size]   = entry;
 105   new_environ[size+1] = NULL;
 106
 107   environ = new_environ;
 108
 109   return(0);
 110 }