getenv

GETENV(3)                   Linux Programmer's Manual                  GETENV(3)



NAME
       getenv, secure_getenv - get an environment variable

SYNOPSIS
       #include <stdlib.h>

       char *getenv(const char *name);

       char *secure_getenv(const char *name);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       secure_getenv(): _GNU_SOURCE

DESCRIPTION
       The getenv() function searches the environment list to find the
       environment variable name, and returns a pointer to the corresponding
       value string.

       The GNU-specific secure_getenv() function is just like getenv() except
       that it returns NULL in cases where "secure execution" is required.
       Secure execution is required if one of the following conditions was true
       when the program run by the calling process was loaded:

       *  the process's effective user ID did not match its real user ID or the
          process's effective group ID did not match its real group ID
          (typically this is the result of executing a set-user-ID or set-group-
          ID program);

       *  the effective capability bit was set on the executable file; or

       *  the process has a nonempty permitted capability set.

       Secure execution may also be required if triggered by some Linux security
       modules.

       The secure_getenv() function is intended for use in general-purpose
       libraries to avoid vulnerabilities that could occur if set-user-ID or
       set-group-ID programs accidentally trusted the environment.

RETURN VALUE
       The getenv() function returns a pointer to the value in the environment,
       or NULL if there is no match.

VERSIONS
       secure_getenv() first appeared in glibc 2.17.

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────────────────────┬───────────────┬─────────────┐
       │Interface                 Attribute     Value       │
       ├──────────────────────────┼───────────────┼─────────────┤
       │getenv(), secure_getenv() │ Thread safety │ MT-Safe env │
       └──────────────────────────┴───────────────┴─────────────┘
CONFORMING TO
       getenv(): POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

       secure_getenv() is a GNU extension.

NOTES
       The strings in the environment list are of the form name=value.

       As typically implemented, getenv() returns a pointer to a string within
       the environment list.  The caller must take care not to modify this
       string, since that would change the environment of the process.

       The implementation of getenv() is not required to be reentrant.  The
       string pointed to by the return value of getenv() may be statically
       allocated, and can be modified by a subsequent call to getenv(),
       putenv(3), setenv(3), or unsetenv(3).

       The "secure execution" mode of secure_getenv() is controlled by the
       AT_SECURE flag contained in the auxiliary vector passed from the kernel
       to user space.

SEE ALSO
       clearenv(3), getauxval(3), putenv(3), setenv(3), unsetenv(3),
       capabilities(7), environ(7)

COLOPHON
       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



GNU                                2017-09-15                          GETENV(3)