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The open function allows ports to be opened for line access. In line mode, the first function will return a line of text, rather than a character. The example below reads a file one line at a time:
fp: open/lines %file.txt print first fp I wanted the gold, and I got it --
print third fp Yet somehow life's not what I thought it,
The /lines refinement is also useful for Internet protocols that are line oriented.
tp: open/lines tcp://server:8000 print first tp
You can use the /read refinement to open a port as read only:
fp: open/read %file.txt
Changes made to the port's buffer, are not written back to the file.
To open for write only, use the /write refinement:
fp: open/write %file.txt
File ports opened with the /write refinement will not read the current data upon opening the port.
Closing, or updating a write only file port will cause existing data in the file to be overwritten:
insert fp "This is the law of the Yukon..." close fp print read %file.txt This is the law of the Yukon...
The /direct refinement opens an unbuffered port. This is useful to access files a portion at a time, such as when a file is too large to be held in memory.
fp: open/direct %file.txt
Reading the data with a copy function will move the port's head forward:
print copy/part fp 40 I wanted the gold, and I sought it,^/ I
print copy/part fp 40 scrabbled and mucked like a slave.^/Was i
In direct mode, the port will always be at its head position:
print head? fp true
Here is an example that uses direct ports to copy a file of any size:
from-port: open/direct %a-file.jpg to-port: open/direct %a-file.jpg while [data: copy/part from-port 100000 ][ append to-port data ] close from-port close to-port
There are two ways to skip data that exists in a port. First, you can open the port with the /skip refinement. This open function will automatically skip to a point in the port. For example:
fp: open/direct/skip %file.big 1000000 fp: open/skip http://www.example.com/bigfile.dat 100000
You can also use the skip function on the port. For files that are opened with /direct and /binary the skip operation is identical to a file system seek operation. Data is not read into memory. This is not possible in /string mode because the line breaks interfere with the skip size.
fp: open/direct/binary %file.dat fp: skip fp 100000
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