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man:getenv

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 envi-
     ronment 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 secu-
     rity 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  environ-
     ment, 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 |
     +--------------------------+---------------+-------------+

CONFORMING TO

     getenv(): POSIX.1-2001, POSIX.1-2008, C89, 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), capabili-
     ties(7), environ(7)

COLOPHON

     This  page  is  part of release 4.16 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
     https://www.kernel.org/doc/man-pages/.

GNU 2017-09-15 GETENV(3)

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