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appendopens the file for writing, positioning the file pointer at the end. Mode
updateopens the file for writing, positioning the file pointer at the beginning of the file without truncating the file. Stream is either a variable, in which case it is bound to an integer identifying the stream, or an atom, in which case this atom will be the stream identifier.88New code should use the
alias(Alias)option for compatibility with the ISO standard.
SWI-Prolog also allows SrcDest to be a term
In this form, Command is started as a child process and if
write, output written to Stream
is sent to the standard input of Command. Viso versa, if Mode
read, data written by Command to the standard
output may be read from Stream. On Unix systems, Command
is handed to popen() which hands it to the Unix shell. On Windows, Command
is executed directly. See also process_create/3
If SrcDest is an IRI, i.e., starts with
://, where <scheme>
is a non-empty sequence of lowercase ASCII letters open/3,4
calls hooks registered by register_iri_scheme/3.
Currently the only predefined IRI scheme is
access to the resource database. See
The following Options are recognised by open/4:
?- open(data, read, Fd, [alias(input)]). ..., read(input, Term), ...
write. See also stream_property/2 and especially section 188.8.131.52 for a discussion of this feature.
full(default) defines full buffering,
linebuffering by line, and
falseimplies the stream is fully unbuffered. Smaller buffering is useful if another process or the user is waiting for the output as it is being produced. See also flush_output/[0,1]. This option is not an ISO option.
true(default), the stream is closed on an abort (see abort/0). If
false, the stream is not closed. If it is an output stream, however, it will be flushed. Useful for logfiles and if the stream is associated to a process (using the
updatemode. Currently, List is a list of atoms that describe the permissions of the created file.89Added after feedback from Joachim Shimpf and Per Mildner. Defined values are below. Not recognised values are silently ignored, allowing for adding platform specific extensions to this set.
Note that if List is empty, the created file has no
associated access permissions. The create options map to the POSIX mode
option of open(), where
read map to 0444,
to 0222 and
execute to 0111. On POSIX systems, the final
permission is defined as (mode &
textis derived from the Prolog flag encoding. For
binarystreams the default encoding is
octet. For details on encoding issues, see section 2.20.1.
eof_code, which makes get0/1 and friends return -1, and read/1 and friends return the atom
end_of_file. Repetitive reading keeps yielding the same result. Action
eof_code, but repetitive reading will raise an error. With action
reset, Prolog will examine the file again and return more data if the file has grown.
none, which does not lock the file. The value
sharedmeans other processes may read the file, but not write it. The value
exclusivemeans no other process may read or write the file.
Locks are acquired through the POSIX function fcntl() using the
F_SETLKW, which makes a blocked call wait for the lock to
be released. Please note that fcntl() locks are advisory and
therefore only other applications using the same advisory locks honour
your lock. As there are many issues around locking in Unix, especially
related to NFS (network file system), please study the fcntl() manual
page before trusting your locks!
lock option is a SWI-Prolog extension.
text(default), Prolog will write a text file in an operating system compatible way. Using type
binarythe bytes will be read or written without any translation. See also the option
true), the open call returns immediately with an exception if the file is locked. The exception has the format
permission_error(lock, source_sink, SrcDest).
reposition is not supported in SWI-Prolog.
All streams connected to a file may be repositioned.