Reading and Writing Files

This example shows how to read and write files in the filesystem.

Reading a Text File

The IO.File object represents a file in the filesystem, we can read from this file via its reader object:

infile <- IO.File("testread.txt")
reader <- infile.reader()

The reader object has a number of methods for reading data, the easiest for reading text is often the lines() method which returns an interator:

foreach(line in reader.lines()) {
	println(line)
}

We can also use a foreach loop directly on the reader object to iterate over the utf-8 characters in the file.

Reading a Binary File

Reading from a file with arbitrary binary data is also possible using the same reader object. In this case we use methods that read in various types as binary data:

binreader <- IO.File("testread.dat").reader()
println("float value: " + binreader.float())
println("string value: " + binreader.string())
println("boolean value: " + binreader.boolean())
println("integer value: " + binreader.integer())

Writing Files

In order to write files we use the writer object. This object can write both text and binary data to a file, to write text, use the print or println methods:

writer <- IO.File("testwrite.txt").writer()
writer.println("Hello")
writer.println("123")

In order to write binary data of any primitive type use the write method:

binwriter <- IO.File("testwrite.dat").writer()
binwriter.write(1.33)
binwriter.write("a string")
binwriter.write(true)
binwriter.write(100)

Writing Custom Values

Note that integers are 8 bytes long, if we want to write shorter values we cannot simply write them as integers but we can use the buffer object to get around this limitation.

Buffer objects also have readers and writers so we can write our integer to an 8-byte buffer, just large enough to hold it. Then we use the buffer slice method to return the first four bytes:

function makeit4(ival) {
	local buffer = buffer(8)
	buffer.writer().write(ival)
	return buffer.slice(0, 4)
}

(Note we have made some assumptions on endianness here!)

The result can simply be written as a buffer:

local iwriter = IO.File("testsmallint.dat").writer()
local myint = 234
iwriter.write(makeit4(myint))

File Handles

When reading or writing a file as above the underlying file handle is tied to the lifecycle of the reader or writer object, and will be closed when this object goes out of scope. There is usually no need to explicitly close the file and nothing more needs to be done in the script.

The exception to this happens when writing and then later reading the same file in the same script, due to buffering the reader may fail to read any data if the writer had not closed its underlying file handle.

One solution is to define the writer as a local variable within a method, when the method returns the writer will go out of scope and close the file handle.

It is also possible to explicitly close the file handle via setting the variable to null (or any other value):

rwfile <- IO.File("testfilehandle.dat")

local writer = rwfile.writer()
writer.write("string")
writer.write(3.333)

writer = null // need this to close file

local reader = rwfile.reader()
println(reader.string())
println(reader.float())

Complete Script

infile <- IO.File("testread.txt")
reader <- infile.reader()

foreach(line in reader.lines()) {
	println(line)
}

binreader <- IO.File("testread.dat").reader()
println("float value: " + binreader.float())
println("string value: " + binreader.string())
println("boolean value: " + binreader.boolean())
println("integer value: " + binreader.integer())

writer <- IO.File("testwrite.txt").writer()
writer.println("Hello")
writer.println("123")

binwriter <- IO.File("testwrite.dat").writer()
binwriter.write(1.33)
binwriter.write("a string")
binwriter.write(true)
binwriter.write(100)

function makeit4(ival) {
	local buffer = buffer(8)
	buffer.writer().write(ival)
	return buffer.slice(0, 4)
}

local iwriter = IO.File("testsmallint.dat").writer()
local myint = 234
iwriter.write(makeit4(myint))

rwfile <- IO.File("testfilehandle.dat")

local writer = rwfile.writer()
writer.write("string")
writer.write(3.333)

writer = null // need this to close file

local reader = rwfile.reader()
println(reader.string())
println(reader.float())