setenv(3) — Linux manual page


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

       setenv(), unsetenv():
           _POSIX_C_SOURCE >= 200112L
               || /* Glibc <= 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 putenv(3)).

       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

       setenv() and unsetenv() functions return zero on success, or -1
       on error, with errno set to indicate 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

ATTRIBUTES         top

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

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

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 5.13 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                            2021-03-22                      SETENV(3)

Pages that refer to this page: ul(1)clearenv(3)getenv(3)pmgetconfig(3)putenv(3)environ(7)