getenv, secure_getenv - get an environment variable


   #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


   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 required if triggered by some Linux security

   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.


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


   secure_getenv() first appeared in glibc 2.17.


   For   an   explanation   of   the  terms  used  in  this  section,  see

   Interface                  Attribute      Value       
   getenv(), secure_getenv()  Thread safety  MT-Safe env 


   getenv(): POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

   secure_getenv() is a GNU extension.


   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.


   clearenv(3),    getauxval(3),    putenv(3),   setenv(3),   unsetenv(3),
   capabilities(7), environ(7)


   This page is part of release 4.09 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


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.