lib/unsetenv.c

   1 /* Copyright (C) 1992, 1995-2002, 2005-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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 Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Don't use __attribute__ __nonnull__ in this compilation unit.  Otherwise gcc
  18    optimizes away the name == NULL test below.  */
  19 #define _GL_ARG_NONNULL(params)
  20
  21 #include <config.h>
  22
  23 /* Specification.  */
  24 #include <stdlib.h>
  25
  26 #include <errno.h>
  27 #if !_LIBC
  28 # define __set_errno(ev) ((errno) = (ev))
  29 #endif
  30
  31 #include <string.h>
  32 #include <unistd.h>
  33
  34 #if !_LIBC
  35 # define __environ      environ
  36 #endif
  37
  38 #if _LIBC
  39 /* This lock protects against simultaneous modifications of 'environ'.  */
  40 # include <bits/libc-lock.h>
  41 __libc_lock_define_initialized (static, envlock)
  42 # define LOCK   __libc_lock_lock (envlock)
  43 # define UNLOCK __libc_lock_unlock (envlock)
  44 #else
  45 # define LOCK
  46 # define UNLOCK
  47 #endif
  48
  49 /* In the GNU C library we must keep the namespace clean.  */
  50 #ifdef _LIBC
  51 # define unsetenv __unsetenv
  52 #endif
  53
  54 #if _LIBC || !HAVE_UNSETENV
  55
  56 int
  57 unsetenv (const char *name)
  58 {
  59   size_t len;
  60
  61   if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
  62     {
  63       __set_errno (EINVAL);
  64       return -1;
  65     }
  66
  67   len = strlen (name);
  68
  69 #if HAVE_DECL__PUTENV /* native Windows */
  70   /* The Microsoft documentation
  71      <https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/putenv-wputenv>
  72      says:
  73        "Don't change an environment entry directly: instead,
  74         use _putenv or _wputenv to change it."
  75      Note: Microsoft's _putenv updates not only the contents of _environ but
  76      also the contents of _wenviron, so that both are in kept in sync.
  77
  78      The way to remove an environment variable is to pass to _putenv a string
  79      of the form "NAME=".  (NB: This is a different convention than with glibc
  80      putenv, which expects a string of the form "NAME"!)  */
  81   {
  82     int putenv_result;
  83     char *name_ = malloc (len + 2);
  84     if (name_ == NULL)
  85       return -1;
  86     memcpy (name_, name, len);
  87     name_[len] = '=';
  88     name_[len + 1] = 0;
  89     putenv_result = _putenv (name_);
  90     /* In this particular case it is OK to free() the argument passed to
  91        _putenv.  */
  92     free (name_);
  93     return putenv_result;
  94   }
  95 #else
  96
  97   LOCK;
  98
  99   char **ep = __environ;
 100   while (*ep != NULL)
 101     if (!strncmp (*ep, name, len) && (*ep)[len] == '=')
 102       {
 103         /* Found it.  Remove this pointer by moving later ones back.  */
 104         char **dp = ep;
 105
 106         do
 107           dp[0] = dp[1];
 108         while (*dp++);
 109         /* Continue the loop in case NAME appears again.  */
 110       }
 111     else
 112       ++ep;
 113
 114   UNLOCK;
 115
 116   return 0;
 117 #endif
 118 }
 119
 120 #ifdef _LIBC
 121 # undef unsetenv
 122 weak_alias (__unsetenv, unsetenv)
 123 #endif
 124
 125 #else /* HAVE_UNSETENV */
 126
 127 # undef unsetenv
 128 # if !HAVE_DECL_UNSETENV
 129 #  if VOID_UNSETENV
 130 extern void unsetenv (const char *);
 131 #  else
 132 extern int unsetenv (const char *);
 133 #  endif
 134 # endif
 135
 136 /* Call the underlying unsetenv, in case there is hidden bookkeeping
 137    that needs updating beyond just modifying environ.  */
 138 int
 139 rpl_unsetenv (const char *name)
 140 {
 141   int result = 0;
 142   if (!name || !*name || strchr (name, '='))
 143     {
 144       errno = EINVAL;
 145       return -1;
 146     }
 147   while (getenv (name))
 148 # if !VOID_UNSETENV
 149     result =
 150 # endif
 151       unsetenv (name);
 152   return result;
 153 }
 154
 155 #endif /* HAVE_UNSETENV */