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 effec‐
          tive group ID did not match its real group ID (typically this is the result of  execut‐
          ing 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 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.

CONFORMING TO
       getenv(): SVr4, POSIX.1-2001, 4.3BSD, C89, C99.

       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 subse‐
       quent call to getenv(), putenv(3), setenv(3), or unsetenv(3).

       The "secure execution" mode of secure_getenv() is controlled by the  AT_SECURE  flag  con‐
       tained 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 3.74 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 http://www.kernel.org/doc/man-pages/.



GNU                                         2012-08-14                                  GETENV(3)