получить переменную окружения (get an environment variable)
Имя (Name)
getenv, secure_getenv - get an environment variable
Синопсис (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
Описание (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.
Возвращаемое значение (Return value)
The getenv() function returns a pointer to the value in the
environment, or NULL if there is no match.
Версии (Versions)
secure_getenv() first appeared in glibc 2.17.
Атрибуты (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 │
└──────────────────────────────────┴───────────────┴─────────────┘
Стандарты (Conforming to)
getenv(): POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
secure_getenv() is a GNU extension.
Примечание (Note)
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.
Смотри также (See also)
clearenv(3), getauxval(3), putenv(3), setenv(3), unsetenv(3),
capabilities(7), environ(7)
