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/*-------------------------------------------------------------------------
*
* unsetenv.c
* unsetenv() emulation for machines without it
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/port/unsetenv.c
*
*-------------------------------------------------------------------------
*/
#include "c.h"
int
unsetenv(const char *name)
{
char *envstr;
/* Error conditions, per POSIX */
if (name == NULL || name[0] == '\0' || strchr(name, '=') != NULL)
{
errno = EINVAL;
return -1;
}
if (getenv(name) == NULL)
return 0; /* no work */
/*
* The technique embodied here works if libc follows the Single Unix Spec
* and actually uses the storage passed to putenv() to hold the environ
* entry. When we clobber the entry in the second step we are ensuring
* that we zap the actual environ member. However, there are some libc
* implementations (notably recent BSDs) that do not obey SUS but copy the
* presented string. This method fails on such platforms. Hopefully all
* such platforms have unsetenv() and thus won't be using this hack. See:
* http://www.greenend.org.uk/rjk/2008/putenv.html
*
* Note that repeatedly setting and unsetting a var using this code will
* leak memory.
*/
envstr = (char *) malloc(strlen(name) + 2);
if (!envstr) /* not much we can do if no memory */
return -1;
/* Override the existing setting by forcibly defining the var */
sprintf(envstr, "%s=", name);
if (putenv(envstr))
return -1;
/* Now we can clobber the variable definition this way: */
strcpy(envstr, "=");
/*
* This last putenv cleans up if we have multiple zero-length names as a
* result of unsetting multiple things.
*/
return putenv(envstr);
}
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