1 /*-------------------------------------------------------------------------
2 *
3 * unsetenv.c
4 * unsetenv() emulation for machines without it
5 *
6 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
8 *
9 *
10 * IDENTIFICATION
11 * src/port/unsetenv.c
12 *
13 *-------------------------------------------------------------------------
14 */
15
16 #include "c.h"
17
18
19 void
unsetenv(const char * name)20 unsetenv(const char *name)
21 {
22 char *envstr;
23
24 if (getenv(name) == NULL)
25 return; /* no work */
26
27 /*
28 * The technique embodied here works if libc follows the Single Unix Spec
29 * and actually uses the storage passed to putenv() to hold the environ
30 * entry. When we clobber the entry in the second step we are ensuring
31 * that we zap the actual environ member. However, there are some libc
32 * implementations (notably recent BSDs) that do not obey SUS but copy the
33 * presented string. This method fails on such platforms. Hopefully all
34 * such platforms have unsetenv() and thus won't be using this hack. See:
35 * http://www.greenend.org.uk/rjk/2008/putenv.html
36 *
37 * Note that repeatedly setting and unsetting a var using this code will
38 * leak memory.
39 */
40
41 envstr = (char *) malloc(strlen(name) + 2);
42 if (!envstr) /* not much we can do if no memory */
43 return;
44
45 /* Override the existing setting by forcibly defining the var */
46 sprintf(envstr, "%s=", name);
47 putenv(envstr);
48
49 /* Now we can clobber the variable definition this way: */
50 strcpy(envstr, "=");
51
52 /*
53 * This last putenv cleans up if we have multiple zero-length names as a
54 * result of unsetting multiple things.
55 */
56 putenv(envstr);
57 }
58