NAME

       getenv, secure_getenv - get an environment variable

LIBRARY

       Standard C library (libc, -lc)

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 │
       └───────────────────────────────────────────────────────────┴───────────────┴─────────────┘

STANDARDS

       getenv(): POSIX.1-2001, POSIX.1-2008, 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)