unsetenv(3)                                                 unsetenv(3)

  getenv()

  NAME

    getenv(), putenv(), setenv(), unsetenv() - environment variable functions

  SYNOPSIS

    #include 

    char * getenv (const char *name)
    int putenv (char *string)
    int setenv (const char *name, const char *value, int overwrite)
    int unsetenv (const char *name)

  DESCRIPTION

    These functions set, fetch, and remove environment variables from the host
    environment list.

    The getenv(3) function obtains the current value of the environment
    variable, name. If the variable name is not in the current environment, a
    null pointer is returned.

    The putenv(3) function inserts or resets an environment variable in the
    current environment list. The form of the argument string is name=value.
    If the environment variable name does not exist in the list, it is
    inserted with the given value. If it does exist, its value is replaced.

    The setenv(3) function inserts or resets the environment variable name in
    the current environment list. If the variable name does not exist in the
    list, it is inserted with the given value. If the variable does exist, the
    argument overwrite is tested; if overwrite is zero, the variable is not
    reset; otherwise, it is reset to the given value.

    The unsetenv(3) function removes the environment variable name from the
    current environment list. It is not an error if the named variable does
    not exist in the current environment.

  RETURN VALUES

    The putenv(3), setenv(3), and unsetenv(3) functions return zero if
    successful; otherwise the global variable errno is set to indicate the
    error and a -1 is returned.

  ERRORS

    [EINVAL]
        The name argument is a null pointer, points to an empty string, or
        points to a string containing an equal sign (=) character.

    [ENOMEM]
        The putenv(3) and setenv(3) functions were unable to allocate memory
        for the environment.

  SEE ALSO

    sh(1)

    exec(2)

  USAGE NOTES

    None of these functions are thread safe.

    None of these functions are async-signal safe.