True if File exists and can be accessed by this Prolog
process under mode Mode. Mode is one of the atoms
read, write, append, execute,
search, exist, or none. Fails
silently otherwise.
File may also be the name of a directory.
access_file(File, none) simply succeeds without testing
anything.
If Mode is write or append, this
predicate also succeeds if the file does not exist and the user has
write access to the directory of the specified location.
The mode execute is only intended for use with regular
files and the mode search only with directories. However,
the two modes are currently equivalent and both can be used with either
files or directories. This may change in the future, so the results of
checking execute access on directories or search
access on regular files should not be relied on.
The behaviour is backed up by the POSIX access() API. The Windows
replacement (_waccess()) returns incorrect results because it does not
consider ACLs (Access Control Lists). The Prolog flag
win_file_access_check
may be used to control the level of checking performed by Prolog. Please
note that checking access never provides a guarantee that a subsequent
open succeeds without errors due to inherent concurrency in file
operations. It is generally more robust to try and open the file and
handle possible exceptions. See open/4
and
catch/3.
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