SETENV(3)                 Linux Programmer's Manual                SETENV(3)

NAME         top

       setenv - change or add an environment variable

SYNOPSIS         top

       #include <stdlib.h>

       int setenv(const char *name, const char *value, int overwrite);

       int unsetenv(const char *name);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       setenv(), unsetenv():
           _POSIX_C_SOURCE >= 200112L
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE

DESCRIPTION         top

       The setenv() function adds the variable name to the environment with
       the value value, if name does not already exist.  If name does exist
       in the environment, then its value is changed to value if overwrite
       is nonzero; if overwrite is zero, then the value of name is not
       changed (and setenv() returns a success status).  This function makes
       copies of the strings pointed to by name and value (by contrast with

       The unsetenv() function deletes the variable name from the
       environment.  If name does not exist in the environment, then the
       function succeeds, and the environment is unchanged.

RETURN VALUE         top

       The setenv() function returns zero on success, or -1 on error, with
       errno set to indicate the cause of the error.

       The unsetenv() function returns zero on success, or -1 on error, with
       errno set to indicate the cause of the error.

ERRORS         top

       EINVAL name is NULL, points to a string of length 0, or contains an
              '=' character.

       ENOMEM Insufficient memory to add a new variable to the environment.

ATTRIBUTES         top

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

       │Interface  Attribute     Value               │
       │setenv(),  │ Thread safety │ MT-Unsafe const:env │
       │unsetenv() │               │                     │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, 4.3BSD.

NOTES         top

       POSIX.1 does not require setenv() or unsetenv() to be reentrant.

       Prior to glibc 2.2.2, unsetenv() was prototyped as returning void;
       more recent glibc versions follow the POSIX.1-compliant prototype
       shown in the SYNOPSIS.

BUGS         top

       POSIX.1 specifies that if name contains an '=' character, then
       setenv() should fail with the error EINVAL; however, versions of
       glibc before 2.3.4 allowed an '=' sign in name.

SEE ALSO         top

       clearenv(3), getenv(3), putenv(3), environ(7)

COLOPHON         top

       This page is part of release 4.10 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

GNU                              2016-03-15                        SETENV(3)