REBOL 3 Docs Guide Concepts Functions Datatypes Errors
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REBOL 3 Concepts: Ports: Opening a Port

Pending Revision

This document was written for R2 and has yet to be revised for R3.

The Open Function

The open function initializes access to a port according to specified parameters. The function can be supplied with a filename, a URL, or an object. In addition, there are several refinements that will affect the open operation or the access to the port's data.

The simplest method of using open is to provide it with a filename or URL as its argument. In the example below, a file port is opened:

fp: open %file.txt

The fp variable refers to the port. If the port did not open, an error will occur. If necessary, the error can be caught with the try function.

By default the file is opened as buffered. This means that the file is accessed and modified in memory and changes to the file are not written out until the port is closed or updated.

For files, the open function will automatically create the file if it does not already exist.

close open %somefile.txt
if exists? %somefile.txt [print "somefile exists"]
somefile exists

The /new refinement can be used to overwrite an existing file.

write %somefile.txt "text in some file"
print read %somefile.txt
text in some file
close insert open/new %somefile.txt "new data"
print read %somefile.txt
new data

Once a port is open, the series operations such as copy, insert, remove, clear, first, next, and length? can be used to access and change the contents the port.

Open Refinements

The open function accepts a number of refinements that can be used to modify its operation:

/binaryport data is binary
/stringport data is text, translate all line terminators
/withspecify an alternate line termination
/lineshandle data a line at a time or as a block of lines
/directdo not buffer the port
/newcreate or recreate the target of the port
/readopen for read only operation
/writeopen for write only operation
/no-waitdo not wait for data
/skipskip part of the data
/allowspecify protection attributes of files
/customallow special refinements

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