file_spec

    A character string that gives an OpenVMS or UNIX style file
    specification. The usual defaults and logical name translations
    are applied to the file specification.

 mode

    Interpreted as shown in Interpretation of the mode Argument.

    Table REF-1 Interpretation of the mode Argument

    Mode
    Argument     Access Mode

    F_OK         Tests to see if the file exists
    X_OK         Execute
    W_OK         Write (implies delete access)
    R_OK         Read

    Combinations of access modes are indicated by ORing the values.
    For example, to check to see if a file has RWED access mode,
    invoke access as follows:

    access (file_spec, R_OK | W_OK | X_OK);