1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
2 .\" and Copyright (C) 2007, 2012 Michael Kerrisk <mtk.manpages@gmail.com>
4 .\" %%%LICENSE_START(VERBATIM)
5 .\" Permission is granted to make and distribute verbatim copies of this
6 .\" manual provided the copyright notice and this permission notice are
7 .\" preserved on all copies.
9 .\" Permission is granted to copy and distribute modified versions of this
10 .\" manual under the conditions for verbatim copying, provided that the
11 .\" entire resulting derived work is distributed under the terms of a
12 .\" permission notice identical to this one.
14 .\" Since the Linux kernel and libraries are constantly changing, this
15 .\" manual page may be incorrect or out-of-date. The author(s) assume no
16 .\" responsibility for errors or omissions, or for damages resulting from
17 .\" the use of the information contained herein. The author(s) may not
18 .\" have taken the same level of care in the production of this manual,
19 .\" which is licensed free of charge, as they might when working
22 .\" Formatted or processed versions of this manual, if unaccompanied by
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26 .\" References consulted:
27 .\" Linux libc source code
28 .\" Lewine's "POSIX Programmer's Guide" (O'Reilly & Associates, 1991)
30 .\" Modified Sat Jul 24 19:30:29 1993 by Rik Faith (faith@cs.unc.edu)
31 .\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
33 .TH GETENV 3 2017-09-15 "GNU" "Linux Programmer's Manual"
35 getenv, secure_getenv \- get an environment variable
38 .B #include <stdlib.h>
40 .BI "char *getenv(const char *" name );
42 .BI "char *secure_getenv(const char *" name );
46 Feature Test Macro Requirements for glibc (see
47 .BR feature_test_macros (7)):
55 function searches the environment list to find the
58 and returns a pointer to the corresponding
66 except that it returns NULL in cases where "secure execution" is required.
67 Secure execution is required if one of the following conditions
68 was true when the program run by the calling process was loaded:
70 the process's effective user ID did not match its real user ID or
71 the process's effective group ID did not match its real group ID
72 (typically this is the result of executing a set-user-ID or
73 set-group-ID program);
75 the effective capability bit was set on the executable file; or
77 the process has a nonempty permitted capability set.
79 Secure execution may also be required if triggered
80 by some Linux security modules.
84 function is intended for use in general-purpose libraries
85 to avoid vulnerabilities that could occur if
86 set-user-ID or set-group-ID programs accidentally
87 trusted the environment.
91 function returns a pointer to the value in the
92 environment, or NULL if there is no match.
95 first appeared in glibc 2.17.
97 For an explanation of the terms used in this section, see
103 Interface Attribute Value
107 T} Thread safety MT-Safe env
111 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
116 The strings in the environment list are of the form \fIname=value\fP.
118 As typically implemented,
120 returns a pointer to a string within the environment list.
121 The caller must take care not to modify this string,
122 since that would change the environment of the process.
124 The implementation of
126 is not required to be reentrant.
127 The string pointed to by the return value of
129 may be statically allocated,
130 and can be modified by a subsequent call to
137 The "secure execution" mode of
141 flag contained in the auxiliary vector passed from the kernel to user space.
148 .BR capabilities (7),