getenv(3) — Linux manual page

NAME \| LIBRARY \| SYNOPSIS \| DESCRIPTION \| RETURN VALUE \| ATTRIBUTES \| STANDARDS \| HISTORY \| NOTES \| SEE ALSO \| COLOPHON

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).
       ┌──────────────────────────────────┬───────────────┬─────────────┐
       │ 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), 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.

COLOPHON top

       This page is part of the man-pages (Linux kernel and C library
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Linux man-pages 6.15            2025-05-17                      getenv(3)

getenv(3) — Linux manual page

NAME top

LIBRARY top

SYNOPSIS top

DESCRIPTION top

RETURN VALUE top

ATTRIBUTES top

STANDARDS top

HISTORY top

NOTES top

SEE ALSO top

COLOPHON top