Method: Kernel#open

Defined in:

io.c

#open(path[, mode [, perm]][, opt]) ⇒ IO^? #open(path[, mode [, perm]][, opt]) {|io| ... } ⇒ Object

Creates an IO object connected to the given stream, file, or subprocess.

If path does not start with a pipe character (|), treat it as the name of a file to open using the specified mode (defaulting to “r”).

The mode is either a string or an integer. If it is an integer, it must be bitwise-or of open(2) flags, such as File::RDWR or File::EXCL. If it is a string, it is either “fmode”, “fmode:ext_enc”, or “fmode:ext_enc:int_enc”.

See the documentation of IO.new for full documentation of the mode string directives.

If a file is being created, its initial permissions may be set using the perm parameter. See File.new and the open(2) and chmod(2) man pages for a description of permissions.

If a block is specified, it will be invoked with the IO object as a parameter, and the IO will be automatically closed when the block terminates. The call returns the value of the block.

If path starts with a pipe character ("|"), a subprocess is created, connected to the caller by a pair of pipes. The returned IO object may be used to write to the standard input and read from the standard output of this subprocess.

If the command following the pipe is a single minus sign ("|-"), Ruby forks, and this subprocess is connected to the parent. If the command is not "-", the subprocess runs the command.

When the subprocess is ruby (opened via "|-"), the open call returns nil. If a block is associated with the open call, that block will run twice — once in the parent and once in the child.

The block parameter will be an IO object in the parent and nil in the child. The parent’s IO object will be connected to the child’s $stdin and $stdout. The subprocess will be terminated at the end of the block.

Examples

Reading from “testfile”:

open("testfile") do |f|
  print f.gets
end

Produces:

This is line one

Open a subprocess and read its output:

cmd = open("|date")
print cmd.gets
cmd.close

Produces:

Wed Apr  9 08:56:31 CDT 2003

Open a subprocess running the same Ruby program:

f = open("|-", "w+")
if f == nil
  puts "in Child"
  exit
else
  puts "Got: #{f.gets}"
end

Produces:

Got: in Child

Open a subprocess using a block to receive the IO object:

open "|-" do |f|
  if f then
    # parent process
    puts "Got: #{f.gets}"
  else
    # child process
    puts "in Child"
  end
end

Produces:

Got: in Child

Overloads:

• #open(path[, mode [, perm]][, opt]) ⇒ IO^?

  Returns:

  • (IO, nil)
• #open(path[, mode [, perm]][, opt]) {|io| ... } ⇒ Object

  Yields:

  • (io)

  Returns:

  • (Object)

# File 'io.c', line 6541

static VALUE
rb_f_open(int argc, VALUE *argv)
{
    ID to_open = 0;
    int redirect = FALSE;

    if (argc >= 1) {
	CONST_ID(to_open, "to_open");
	if (rb_respond_to(argv[0], to_open)) {
	    redirect = TRUE;
	}
	else {
	    VALUE tmp = argv[0];
	    FilePathValue(tmp);
	    if (NIL_P(tmp)) {
		redirect = TRUE;
	    }
	    else {
                VALUE cmd = check_pipe_command(tmp);
                if (!NIL_P(cmd)) {
		    argv[0] = cmd;
		    return rb_io_s_popen(argc, argv, rb_cIO);
		}
	    }
	}
    }
    if (redirect) {
	VALUE io = rb_funcall2(argv[0], to_open, argc-1, argv+1);

	if (rb_block_given_p()) {
	    return rb_ensure(rb_yield, io, io_close, io);
	}
	return io;
    }
    return rb_io_s_open(argc, argv, rb_cFile);
}