method

open

v1_8_6_287 - Show latest stable - 4 notes - Class: IO

open(...) 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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/*
 *  call-seq:
 *     IO.open(fd, mode_string="r" )               => io
 *     IO.open(fd, mode_string="r" ) {|io| block } => obj
 *  
 *  With no associated block, <code>open</code> is a synonym for
 *  <code>IO::new</code>. If the optional code block is given, it will
 *  be passed <i>io</i> as an argument, and the IO object will
 *  automatically be closed when the block terminates. In this instance,
 *  <code>IO::open</code> returns the value of the block.
 *     
 */

static VALUE
rb_io_s_open(argc, argv, klass)
    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)