method

open

v1_9_2_180 - Show latest stable - 4 notes - Class: IO

open(*args) public

With no associated block, open is a synonym for IO.new. If the optional code block is given, it will be passed io as an argument, and the IO object will automatically be closed when the block terminates. In this instance, IO.open returns the value of the block.

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static VALUE
rb_io_s_open(int argc, VALUE *argv, VALUE klass)
{
    VALUE io = rb_class_new_instance(argc, argv, klass);

    if (rb_block_given_p()) {
        return rb_ensure(rb_yield, io, io_close, io);
    }

    return io;
}

January 14, 2009

6 thanks

File open permissions

Usage: File.open path, flags, [permissions]

Flags (bitmasks)

Access:

`File::RDONLY`	Read-only
`File::WRONLY`	Write-only
`File::RDWR`	Read and write

If the file exists:

`File::TRUNC`	Truncate
`File::APPEND`	Append
`File::EXCL`	Fail

If the file doesn’t exist:

File::CREAT

Create

Flags (strings)

r	`File::RDONLY`
r+	`File::RDWR`
w	`File::WRONLY\|File::TRUNC\|File::CREAT`
a	`File::WRONLY\|File::APPEND\|File::CREAT`

Examples

File.open path, File::RDONLY
File.open path, 'w'
File.open path, File::WRONLY|File::TRUNC|File::CREAT
File.open path, File::WRONLY|File::TRUNC|File::CREAT, '0666'

February 12, 2009

4 thanks

Binary files

Another real important flag is b when dealing with binary files. For example to download an mp3 from the internet you need to pass the b flag or the data will be screwed up:

# Downloads a binary file from the internet
require 'open-uri'
url = "http://fubar/song.mp3"
open(url, 'rb') do |mp3|
  File.open("local.mp3", 'wb') do |file|
    file.write(mp3.read)
  end
end

Don’t say you haven’t been warned. :)

April 21, 2010

0 thanks

Errors Raised

Non IO errors (IOError) are contained in the Errno module. They are the same as those given in open(2), see:

http://www.kernel.org/doc/man-pages/online/pages/man2/open.2.html#ERRORS

Common Errors

Errno::ENOENT: No such file or directory
Errno::EACCES: Permission denied
Errno::EEXIST: File exists (i.e. IO::EXCL | IO::CREAT)