getenv(3) - Linux manual page (original) (raw)

getenv(3) Library Functions Manual getenv(3)

NAME top

   getenv, secure_getenv - get an environment variable

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#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 top

   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 top

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

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────┬───────────────┬─────────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────┼───────────────┼─────────────┤
   │ **getenv**(), **secure_getenv**()        │ Thread safety │ MT-Safe env │
   └──────────────────────────────────┴───────────────┴─────────────┘

STANDARDS top

   **getenv**()
          C11, POSIX.1-2008.

   **secure_getenv**()
          GNU.

HISTORY top

   **getenv**()
          POSIX.1-2001, C89, C99, SVr4, 4.3BSD.

   **secure_getenv**()
          glibc 2.17.

NOTES top

   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)](../man3/putenv.3.html), [setenv(3)](../man3/setenv.3.html), or [unsetenv(3)](../man3/unsetenv.3.html).

   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.

COLOPHON top

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Linux man-pages 6.10 2024-07-23 getenv(3)

getenv(3) - Linux manual page (original) (raw)

NAME top

LIBRARY top

SYNOPSIS top

DESCRIPTION top

RETURN VALUE top

ATTRIBUTES top

STANDARDS top

HISTORY top

NOTES top

SEE ALSO top

COLOPHON top