NAME

       setenv - change or add an environment variable

SYNOPSIS

       #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():
           _BSD_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600

DESCRIPTION

       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.  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

       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

       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.

CONFORMING TO

       4.3BSD, POSIX.1-2001.

NOTES

       POSIX.1-2001 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.1-2001-compliant prototype shown in the SYNOPSIS.

BUGS

       POSIX.1-2001 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

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

COLOPHON

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