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IO

The IO class is the basis for all input and output in Ruby. An I/O stream may be duplexed (that is, bidirectional), and so may use more than one native operating system stream.

Many of the examples in this section use the File class, the only standard subclass of IO. The two classes are closely associated. Like the File class, the Socket library subclasses from IO (such as TCPSocket or UDPSocket).

The Kernel#open method can create an IO (or File) object for these types of arguments:

  • A plain string represents a filename suitable for the underlying operating system.

  • A string starting with "|" indicates a subprocess. The remainder of the string following the "|" is invoked as a process with appropriate input/output channels connected to it.

  • A string equal to "|-" will create another Ruby instance as a subprocess.

The IO may be opened with different file modes (read-only, write-only) and encodings for proper conversion. See IO.new for these options. See Kernel#open for details of the various command formats described above.

IO.popen, the Open3 library, or Process#spawn may also be used to communicate with subprocesses through an IO.

Ruby will convert pathnames between different operating system conventions if possible. For instance, on a Windows system the filename "/gumby/ruby/test.rb" will be opened as "\gumby\ruby\test.rb". When specifying a Windows-style filename in a Ruby string, remember to escape the backslashes:

"C:\\gumby\\ruby\\test.rb"

Our examples here will use the Unix-style forward slashes; File::ALT_SEPARATOR can be used to get the platform-specific separator character.

The global constant ARGF (also accessible as $<) provides an IO-like stream which allows access to all files mentioned on the command line (or STDIN if no files are mentioned). ARGF#path and its alias ARGF#filename are provided to access the name of the file currently being read.

io/console ↑

The io/console extension provides methods for interacting with the console. The console can be accessed from IO.console or the standard input/output/error IO objects.

Requiring io/console adds the following methods:

  • IO::console

  • IO#raw

  • IO#raw!

  • IO#cooked

  • IO#cooked!

  • IO#getch

  • IO#echo=

  • IO#echo?

  • IO#noecho

  • IO#winsize

  • IO#winsize=

  • IO#iflush

  • IO#ioflush

  • IO#oflush

Example:

require 'io/console'
rows, columns = $stdout.winsize
puts "Your screen is #{columns} wide and #{rows} tall"

Example Files ↑

Many examples here use these filenames and their corresponding files:

  • t.txt: A text-only file that is assumed to exist via:

    text = <<~EOT
  This is line one.
  This is the second line.
  This is the third line.
EOT
File.write('t.txt', text)

  • t.dat: A data file that is assumed to exist via:

    data = "\u9990\u9991\u9992\u9993\u9994"
f = File.open('t.dat', 'wb:UTF-16')
f.write(data)
f.close

  • t.rus: A Russian-language text file that is assumed to exist via:

    File.write('t.rus', "\u{442 435 441 442}")

  • t.tmp: A file that is assumed not to exist.

Modes ↑

A number of IO method calls must or may specify a mode for the stream; the mode determines how stream is to be accessible, including:

  • Whether the stream is to be read-only, write-only, or read-write.

  • Whether the stream is positioned at its beginning or its end.

  • Whether the stream treats data as text-only or binary.

  • The external and internal encodings.

Mode Specified as an Integer ↑

When mode is an integer it must be one or more (combined by bitwise OR (|) of the modes defined in File::Constants:

  • File::RDONLY: Open for reading only.

  • File::WRONLY: Open for writing only.

  • File::RDWR: Open for reading and writing.

  • File::APPEND: Open for appending only.

  • File::CREAT: Create file if it does not exist.

  • File::EXCL: Raise an exception if File::CREAT is given and the file exists.

Examples:

File.new('t.txt', File::RDONLY)
File.new('t.tmp', File::RDWR | File::CREAT | File::EXCL)

Note: Method IO#set_encoding does not allow the mode to be specified as an integer.

Mode Specified As a String ↑

When mode is a string it must begin with one of the following:

  • 'r': Read-only stream, positioned at the beginning; the stream cannot be changed to writable.

  • 'w': Write-only stream, positioned at the beginning; the stream cannot be changed to readable.

  • 'a': Write-only stream, positioned at the end; every write appends to the end; the stream cannot be changed to readable.

  • 'r+': Read-write stream, positioned at the beginning.

  • 'w+': Read-write stream, positioned at the end.

  • 'a+': Read-write stream, positioned at the end.

For a writable file stream (that is, any except read-only), the file is truncated to zero if it exists, and is created if it does not exist.

Examples:

File.open('t.txt', 'r')
File.open('t.tmp', 'w')

Either of the following may be suffixed to any of the above:

  • 't': Text data; sets the default external encoding to Encoding::UTF_8; on Windows, enables conversion between EOL and CRLF.

  • 'b': Binary data; sets the default external encoding to Encoding::ASCII_8BIT; on Windows, suppresses conversion between EOL and CRLF.

If neither is given, the stream defaults to text data.

Examples:

File.open('t.txt', 'rt')
File.open('t.dat', 'rb')

The following may be suffixed to any writable mode above:

  • 'x': Creates the file if it does not exist; raises an exception if the file exists.

Example:

File.open('t.tmp', 'wx')

Finally, the mode string may specify encodings – either external encoding only or both external and internal encodings – by appending one or both encoding names, separated by colons:

f = File.new('t.dat', 'rb')
f.external_encoding # => #<Encoding:ASCII-8BIT>
f.internal_encoding # => nil
f = File.new('t.dat', 'rb:UTF-16')
f.external_encoding # => #<Encoding:UTF-16 (dummy)>
f.internal_encoding # => nil
f = File.new('t.dat', 'rb:UTF-16:UTF-16')
f.external_encoding # => #<Encoding:UTF-16 (dummy)>
f.internal_encoding # => #<Encoding:UTF-16>

The numerous encoding names are available in array Encoding.name_list:

Encoding.name_list.size    # => 175
Encoding.name_list.take(3) # => ["ASCII-8BIT", "UTF-8", "US-ASCII"]

Encodings ↑

When the external encoding is set, strings read are tagged by that encoding when reading, and strings written are converted to that encoding when writing.

When both external and internal encodings are set, strings read are converted from external to internal encoding, and strings written are converted from internal to external encoding. For further details about transcoding input and output, see Encoding.

If the external encoding is 'BOM|UTF-8', 'BOM|UTF-16LE' or 'BOM|UTF16-BE', Ruby checks for a Unicode BOM in the input document to help determine the encoding. For UTF-16 encodings the file open mode must be binary. If the BOM is found, it is stripped and the external encoding from the BOM is used.

Note that the BOM-style encoding option is case insensitive, so 'bom|utf-8' is also valid.)

Open Options ↑

A number of IO methods accept an optional parameter opts, which determines how a new stream is to be opened:

  • :mode: Stream mode.

  • :flags: Integer file open flags; If mode is also given, the two are bitwise-ORed.

  • :external_encoding: External encoding for the stream.

  • :internal_encoding: Internal encoding for the stream. '-' is a synonym for the default internal encoding. If the value is nil no conversion occurs.

  • :encoding: Specifies external and internal encodings as 'extern:intern'.

  • :textmode: If a truthy value, specifies the mode as text-only, binary otherwise.

  • :binmode: If a truthy value, specifies the mode as binary, text-only otherwise.

  • :autoclose: If a truthy value, specifies that the fd will close when the stream closes; otherwise it remains open.

Also available are the options offered in String#encode, which may control conversion between external internal encoding.

Getline Options ↑

A number of IO methods accept optional keyword arguments that determine how a stream is to be treated:

  • :chomp: If true, line separators are omitted; default is false.

Position ↑

An IO stream has a position, which is the non-negative integer offset (in bytes) in the stream where the next read or write will occur.

Note that a text stream may have multi-byte characters, so a text stream whose position is n (bytes) may not have n characters preceding the current position – there may be fewer.

A new stream is initially positioned:

  • At the beginning (position 0) if its mode is 'r', 'w', or 'r+'.

  • At the end (position self.size) if its mode is 'a', 'w+', or 'a+'.

Methods to query the position:

  • IO#tell and its alias IO#pos return the position for an open stream.

  • IO#eof? and its alias IO#eof return whether the position is at the end of a readable stream.

Reading from a stream usually changes its position:

f = File.open('t.txt')
f.tell     # => 0
f.readline # => "This is line one.\n"
f.tell     # => 19
f.readline # => "This is the second line.\n"
f.tell     # => 45
f.eof?     # => false
f.readline # => "Here's the third line.\n"
f.eof?     # => true

Writing to a stream usually changes its position:

f = File.open('t.tmp', 'w')
f.tell         # => 0
f.write('foo') # => 3
f.tell         # => 3
f.write('bar') # => 3
f.tell         # => 6

Iterating over a stream usually changes its position:

f = File.open('t.txt')
f.each do |line|
  p "position=#{f.pos} eof?=#{f.eof?} line=#{line}"
end

Output:

"position=19 eof?=false line=This is line one.\n"
"position=45 eof?=false line=This is the second line.\n"
"position=70 eof?=true line=This is the third line.\n"

The position may also be changed by certain other methods:

Line Number ↑

A readable IO stream has a line number, which is the non-negative integer line number in the stream where the next read will occur.

A new stream is initially has line number 0.

Method IO#lineno returns the line number.

Reading lines from a stream usually changes its line number:

f = File.open('t.txt', 'r')
f.lineno   # => 0
f.readline # => "This is line one.\n"
f.lineno   # => 1
f.readline # => "This is the second line.\n"
f.lineno   # => 2
f.readline # => "Here's the third line.\n"
f.lineno   # => 3
f.eof?     # => true

Iterating over lines in a stream usually changes its line number:

f = File.open('t.txt')
f.each_line do |line|
  p "position=#{f.pos} eof?=#{f.eof?} line=#{line}"
end

Output:

"position=19 eof?=false line=This is line one.\n"
"position=45 eof?=false line=This is the second line.\n"
"position=70 eof?=true line=This is the third line.\n"

What's Here ↑

First, what's elsewhere. Class IO:

Here, class IO provides methods that are useful for:

Creating ↑

  • ::new (aliased as ::for_fd)

    Creates and returns a new IO object for the given integer file descriptor.

  • ::open

    Creates a new IO object.

  • ::pipe

    Creates a connected pair of reader and writer IO objects.

  • ::popen

    Creates an IO object to interact with a subprocess.

  • ::select

    Selects which given IO instances are ready for reading,

    writing, or have pending exceptions.

Reading ↑

  • ::binread

    Returns a binary string with all or a subset of bytes from the given file.

  • ::read

    Returns a string with all or a subset of bytes from the given file.

  • ::readlines

    Returns an array of strings, which are the lines from the given file.

  • getbyte

    Returns the next 8-bit byte read from self as an integer.

  • getc

    Returns the next character read from self as a string.

  • gets

    Returns the line read from self.

  • pread

    Returns all or the next n bytes read from self, not updating the receiver's offset.

  • read

    Returns all remaining or the next n bytes read from self for a given n.

  • read_nonblock

    the next n bytes read from self for a given n, in non-block mode.

  • readbyte

    Returns the next byte read from self; same as getbyte, but raises an exception on end-of-file.

  • readchar

    Returns the next character read from self; same as getc, but raises an exception on end-of-file.

  • readline

    Returns the next line read from self; same as getline, but raises an exception of end-of-file.

  • readlines

    Returns an array of all lines read read from self.

  • readpartial

    Returns up to the given number of bytes from self.

Writing ↑

  • ::binwrite

    Writes the given string to the file at the given filepath, in binary mode.

  • ::write

    Writes the given string to self.

  • :<<

    Appends the given string to self.

  • print

    Prints last read line or given objects to self.

  • printf

    Writes to self based on the given format string and objects.

  • putc

    Writes a character to self.

  • puts

    Writes lines to self, making sure line ends with a newline.

  • pwrite

    Writes the given string at the given offset, not updating the receiver's offset.

  • write

    Writes one or more given strings to self.

  • write_nonblock

    Writes one or more given strings to self in non-blocking mode.

Positioning ↑

  • lineno

    Returns the current line number in self.

  • lineno=

    Sets the line number is self.

  • pos (aliased as tell)

    Returns the current byte offset in self.

  • pos=

    Sets the byte offset in self.

  • reopen

    Reassociates self with a new or existing IO stream.

  • rewind

    Positions self to the beginning of input.

  • seek

    Sets the offset for self relative to given position.

Iterating ↑

  • ::foreach

    Yields each line of given file to the block.

  • each (aliased as each_line)

    Calls the given block with each successive line in self.

  • each_byte

    Calls the given block with each successive byte in self as an integer.

  • each_char

    Calls the given block with each successive character in self as a string.

  • each_codepoint

    Calls the given block with each successive codepoint in self as an integer.

Settings ↑

Querying ↑

  • autoclose?

    Returns whether self auto-closes.

  • binmode?

    Returns whether self is in binary mode.

  • close_on_exec?

    Returns the close-on-exec flag for self.

  • closed?

    Returns whether self is closed.

  • eof? (aliased as eof)

    Returns whether self is at end-of-file.

  • external_encoding

    Returns the external encoding object for self.

  • fileno (aliased as to_i)

    Returns the integer file descriptor for self

  • internal_encoding

    Returns the internal encoding object for self.

  • pid

    Returns the process ID of a child process associated with self, if self was created by ::popen.

  • stat

    Returns the File::Stat object containing status information for self.

  • sync

    Returns whether self is in sync-mode.

  • tty (aliased as isatty)

    Returns whether self is a terminal.

Buffering ↑

  • fdatasync

    Immediately writes all buffered data in self to disk.

  • flush

    Flushes any buffered data within self to the underlying operating system.

  • fsync

    Immediately writes all buffered data and attributes in self to disk.

  • ungetbyte

    Prepends buffer for self with given integer byte or string.

  • ungetc

    Prepends buffer for self with given string.

Low-Level Access ↑

  • ::sysopen

    Opens the file given by its path, returning the integer file descriptor.

  • advise

    Announces the intention to access data from self in a specific way.

  • fcntl

    Passes a low-level command to the file specified by the given file descriptor.

  • ioctl

    Passes a low-level command to the device specified by the given file descriptor.

  • sysread

    Returns up to the next n bytes read from self using a low-level read.

  • sysseek

    Sets the offset for self.

  • syswrite

    Writes the given string to self using a low-level write.

Other ↑

  • ::copy_stream

    Copies data from a source to a destination, each of which is a filepath or an IO-like object.

  • ::try_convert

    Returns a new IO object resulting from converting the given object.

  • inspect

    Returns the string representation of self.

Constants

EWOULDBLOCKWaitReadable

EAGAINWaitReadable

EWOULDBLOCKWaitWritable

EAGAINWaitWritable

PRIORITY
READABLE
SEEK_CUR

Set I/O position from the current position

SEEK_DATA

Set I/O position to the next location containing data

SEEK_END

Set I/O position from the end

SEEK_HOLE

Set I/O position to the next hole

SEEK_SET

Set I/O position from the beginning

WRITABLE

Public Class Methods

binread(name, [length [, offset]]) → string click to toggle source
binread(name, [length [, offset]]) → string

Opens the file, optionally seeks to the given offset, then returns length bytes (defaulting to the rest of the file). binread ensures the file is closed before returning. The open mode would be "rb:ASCII-8BIT".

If name starts with a pipe character ("|") and the receiver is the IO class, a subprocess is created in the same way as Kernel#open, and its output is returned. Consider to use File.binread to disable the behavior of subprocess invocation.

File.binread("testfile")           #=> "This is line one\nThis is line two\nThis is line three\nAnd so on...\n"
File.binread("testfile", 20)       #=> "This is line one\nThi"
File.binread("testfile", 20, 10)   #=> "ne one\nThis is line "
IO.binread("| cat testfile")       #=> "This is line one\nThis is line two\nThis is line three\nAnd so on...\n"

See also IO.read for details about name and open_args.

 
               static VALUE
rb_io_s_binread(int argc, VALUE *argv, VALUE io)
{
    VALUE offset;
    struct foreach_arg arg;
    enum {
        fmode = FMODE_READABLE|FMODE_BINMODE,
        oflags = O_RDONLY
#ifdef O_BINARY
                |O_BINARY
#endif
    };
    convconfig_t convconfig = {NULL, NULL, 0, Qnil};

    rb_scan_args(argc, argv, "12", NULL, NULL, &offset);
    FilePathValue(argv[0]);
    convconfig.enc = rb_ascii8bit_encoding();
    arg.io = rb_io_open_generic(io, argv[0], oflags, fmode, &convconfig, 0);
    if (NIL_P(arg.io)) return Qnil;
    arg.argv = argv+1;
    arg.argc = (argc > 1) ? 1 : 0;
    if (!NIL_P(offset)) {
        struct seek_arg sarg;
        int state = 0;
        sarg.io = arg.io;
        sarg.offset = offset;
        sarg.mode = SEEK_SET;
        rb_protect(seek_before_access, (VALUE)&sarg, &state);
        if (state) {
            rb_io_close(arg.io);
            rb_jump_tag(state);
        }
    }
    return rb_ensure(io_s_read, (VALUE)&arg, rb_io_close, arg.io);
}
binwrite(name, string, [offset]) → integer click to toggle source
binwrite(name, string, [offset], open_args) → integer
binwrite(name, string, [offset]) → integer
binwrite(name, string, [offset], open_args) → integer

Same as IO.write except opening the file in binary mode and ASCII-8BIT encoding ("wb:ASCII-8BIT").

If name starts with a pipe character ("|") and the receiver is the IO class, a subprocess is created in the same way as Kernel#open, and its output is returned. Consider to use File.binwrite to disable the behavior of subprocess invocation.

See also IO.read for details about name and open_args.

 
               static VALUE
rb_io_s_binwrite(int argc, VALUE *argv, VALUE io)
{
    return io_s_write(argc, argv, io, 1);
}
copy_stream(src, dst) click to toggle source
copy_stream(src, dst, copy_length)
copy_stream(src, dst, copy_length, src_offset)

IO.copy_stream copies src to dst. src and dst is either a filename or an IO-like object. IO-like object for src should have readpartial or read method. IO-like object for dst should have write method. (Specialized mechanisms, such as sendfile system call, may be used on appropriate situation.)

This method returns the number of bytes copied.

If optional arguments are not given, the start position of the copy is the beginning of the filename or the current file offset of the IO. The end position of the copy is the end of file.

If copy_length is given, No more than copy_length bytes are copied.

If src_offset is given, it specifies the start position of the copy.

When src_offset is specified and src is an IO, IO.copy_stream doesn't move the current file offset.

 
               static VALUE
rb_io_s_copy_stream(int argc, VALUE *argv, VALUE io)
{
    VALUE src, dst, length, src_offset;
    struct copy_stream_struct st;

    MEMZERO(&st, struct copy_stream_struct, 1);

    rb_scan_args(argc, argv, "22", &src, &dst, &length, &src_offset);

    st.src = src;
    st.dst = dst;

    st.src_fptr = NULL;
    st.dst_fptr = NULL;

    if (NIL_P(length))
        st.copy_length = (off_t)-1;
    else
        st.copy_length = NUM2OFFT(length);

    if (NIL_P(src_offset))
        st.src_offset = (off_t)-1;
    else
        st.src_offset = NUM2OFFT(src_offset);

    rb_ensure(copy_stream_body, (VALUE)&st, copy_stream_finalize, (VALUE)&st);

    return OFFT2NUM(st.total);
}
for_fd(fd, mode [, opt]) → io click to toggle source

Synonym for IO.new.

 
               static VALUE
rb_io_s_for_fd(int argc, VALUE *argv, VALUE klass)
{
    VALUE io = rb_obj_alloc(klass);
    rb_io_initialize(argc, argv, io);
    return io;
}
foreach(name, sep=$/ [, getline_args, open_args]) {|line| block } → nil click to toggle source
foreach(name, limit [, getline_args, open_args]) {|line| block } → nil
foreach(name, sep, limit [, getline_args, open_args]) {|line| block } → nil
foreach(...) → an_enumerator
foreach(name, sep=$/ [, getline_args, open_args]) {|line| block } → nil
foreach(name, limit [, getline_args, open_args]) {|line| block } → nil
foreach(name, sep, limit [, getline_args, open_args]) {|line| block } → nil
foreach(...) → an_enumerator

Executes the block for every line in the named I/O port, where lines are separated by sep.

If no block is given, an enumerator is returned instead.

If name starts with a pipe character ("|") and the receiver is the IO class, a subprocess is created in the same way as Kernel#open, and its output is returned. Consider to use File.foreach to disable the behavior of subprocess invocation.

File.foreach("testfile") {|x| print "GOT ", x }
IO.foreach("| cat testfile") {|x| print "GOT ", x }

produces:

GOT This is line one
GOT This is line two
GOT This is line three
GOT And so on...

If the last argument is a hash, it's the keyword argument to open. See IO.readlines for details about getline_args. And see also IO.read for details about open_args.

 
               static VALUE
rb_io_s_foreach(int argc, VALUE *argv, VALUE self)
{
    VALUE opt;
    int orig_argc = argc;
    struct foreach_arg arg;
    struct getline_arg garg;

    argc = rb_scan_args(argc, argv, "13:", NULL, NULL, NULL, NULL, &opt);
    RETURN_ENUMERATOR(self, orig_argc, argv);
    extract_getline_args(argc-1, argv+1, &garg);
    open_key_args(self, argc, argv, opt, &arg);
    if (NIL_P(arg.io)) return Qnil;
    extract_getline_opts(opt, &garg);
    check_getline_args(&garg.rs, &garg.limit, garg.io = arg.io);
    return rb_ensure(io_s_foreach, (VALUE)&garg, rb_io_close, arg.io);
}
new(fd [, mode] [, opt]) → io click to toggle source

Returns a new IO object (a stream) for the given integer file descriptor fd and mode string. opt may be used to specify parts of mode in a more readable fashion. See also IO.sysopen and IO.for_fd.

IO.new is called by various File and IO opening methods such as IO::open, Kernel#open, and File::open.

Open Mode ↑

When mode is an integer it must be combination of the modes defined in File::Constants (File::RDONLY, File::WRONLY|File::CREAT). See the open(2) man page for more information.

When mode is a string it must be in one of the following forms:

fmode
fmode ":" ext_enc
fmode ":" ext_enc ":" int_enc
fmode ":" "BOM|UTF-*"

fmode is an IO open mode string, ext_enc is the external encoding for the IO and int_enc is the internal encoding.

IO Open Mode ↑

Ruby allows the following open modes:

"r"  Read-only, starts at beginning of file  (default mode).

"r+" Read-write, starts at beginning of file.

"w"  Write-only, truncates existing file
     to zero length or creates a new file for writing.

"w+" Read-write, truncates existing file to zero length
     or creates a new file for reading and writing.

"a"  Write-only, each write call appends data at end of file.
     Creates a new file for writing if file does not exist.

"a+" Read-write, each write call appends data at end of file.
     Creates a new file for reading and writing if file does
     not exist.

The following modes must be used separately, and along with one or more of the modes seen above.

"b"  Binary file mode
     Suppresses EOL <-> CRLF conversion on Windows. And
     sets external encoding to ASCII-8BIT unless explicitly
     specified.

"t"  Text file mode

The exclusive access mode (“x”) can be used together with “w” to ensure the file is created. Errno::EEXIST is raised when it already exists. It may not be supported with all kinds of streams (e.g. pipes).

When the open mode of original IO is read only, the mode cannot be changed to be writable. Similarly, the open mode cannot be changed from write only to readable.

When such a change is attempted the error is raised in different locations according to the platform.

IO Encoding ↑

When ext_enc is specified, strings read will be tagged by the encoding when reading, and strings output will be converted to the specified encoding when writing.

When ext_enc and int_enc are specified read strings will be converted from ext_enc to int_enc upon input, and written strings will be converted from int_enc to ext_enc upon output. See Encoding for further details of transcoding on input and output.

If “BOM|UTF-8”, “BOM|UTF-16LE” or “BOM|UTF16-BE” are used, Ruby checks for a Unicode BOM in the input document to help determine the encoding. For UTF-16 encodings the file open mode must be binary. When present, the BOM is stripped and the external encoding from the BOM is used. When the BOM is missing the given Unicode encoding is used as ext_enc. (The BOM-set encoding option is case insensitive, so “bom|utf-8” is also valid.)

Options ↑

opt can be used instead of mode for improved readability. The following keys are supported:

:mode

Same as mode parameter

:flags

Specifies file open flags as integer. If mode parameter is given, this parameter will be bitwise-ORed.

:external_encoding

External encoding for the IO.

:internal_encoding

Internal encoding for the IO. “-” is a synonym for the default internal encoding.

If the value is nil no conversion occurs.

:encoding

Specifies external and internal encodings as “extern:intern”.

:textmode

If the value is truth value, same as “t” in argument mode.

:binmode

If the value is truth value, same as “b” in argument mode.

:autoclose

If the value is false, the fd will be kept open after this IO instance gets finalized.

Also, opt can have same keys in String#encode for controlling conversion between the external encoding and the internal encoding.

Example 1 ↑

fd = IO.sysopen("/dev/tty", "w")
a = IO.new(fd,"w")
$stderr.puts "Hello"
a.puts "World"

Produces:

Hello
World

Example 2 ↑

require 'fcntl'

fd = STDERR.fcntl(Fcntl::F_DUPFD)
io = IO.new(fd, mode: 'w:UTF-16LE', cr_newline: true)
io.puts "Hello, World!"

fd = STDERR.fcntl(Fcntl::F_DUPFD)
io = IO.new(fd, mode: 'w', cr_newline: true,
            external_encoding: Encoding::UTF_16LE)
io.puts "Hello, World!"

Both of above print “Hello, World!” in UTF-16LE to standard error output with converting EOL generated by puts to CR.

 
               static VALUE
rb_io_initialize(int argc, VALUE *argv, VALUE io)
{
    VALUE fnum, vmode;
    rb_io_t *fp;
    int fd, fmode, oflags = O_RDONLY;
    convconfig_t convconfig;
    VALUE opt;
#if defined(HAVE_FCNTL) && defined(F_GETFL)
    int ofmode;
#else
    struct stat st;
#endif


    argc = rb_scan_args(argc, argv, "11:", &fnum, &vmode, &opt);
    rb_io_extract_modeenc(&vmode, 0, opt, &oflags, &fmode, &convconfig);

    fd = NUM2INT(fnum);
    if (rb_reserved_fd_p(fd)) {
        rb_raise(rb_eArgError, "The given fd is not accessible because RubyVM reserves it");
    }
#if defined(HAVE_FCNTL) && defined(F_GETFL)
    oflags = fcntl(fd, F_GETFL);
    if (oflags == -1) rb_sys_fail(0);
#else
    if (fstat(fd, &st) < 0) rb_sys_fail(0);
#endif
    rb_update_max_fd(fd);
#if defined(HAVE_FCNTL) && defined(F_GETFL)
    ofmode = rb_io_oflags_fmode(oflags);
    if (NIL_P(vmode)) {
        fmode = ofmode;
    }
    else if ((~ofmode & fmode) & FMODE_READWRITE) {
        VALUE error = INT2FIX(EINVAL);
        rb_exc_raise(rb_class_new_instance(1, &error, rb_eSystemCallError));
    }
#endif
    if (!NIL_P(opt) && rb_hash_aref(opt, sym_autoclose) == Qfalse) {
        fmode |= FMODE_PREP;
    }
    MakeOpenFile(io, fp);
    fp->self = io;
    fp->fd = fd;
    fp->mode = fmode;
    fp->encs = convconfig;
    clear_codeconv(fp);
    io_check_tty(fp);
    if (fileno(stdin) == fd)
        fp->stdio_file = stdin;
    else if (fileno(stdout) == fd)
        fp->stdio_file = stdout;
    else if (fileno(stderr) == fd)
        fp->stdio_file = stderr;

    if (fmode & FMODE_SETENC_BY_BOM) io_set_encoding_by_bom(io);
    return io;
}
open(fd, mode="r" [, opt]) → io click to toggle source
open(fd, mode="r" [, opt]) {|io| block } → obj

With no associated block, IO.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.

See IO.new for a description of the fd, mode and opt parameters.

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

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

    return io;
}
pipe → [read_io, write_io] click to toggle source
pipe(ext_enc) → [read_io, write_io]
pipe("ext_enc:int_enc" [, opt]) → [read_io, write_io]
pipe(ext_enc, int_enc [, opt]) → [read_io, write_io]
pipe(...) {|read_io, write_io| ... }

Creates a pair of pipe endpoints (connected to each other) and returns them as a two-element array of IO objects: [ read_io, write_io ].

If a block is given, the block is called and returns the value of the block. read_io and write_io are sent to the block as arguments. If read_io and write_io are not closed when the block exits, they are closed. i.e. closing read_io and/or write_io doesn't cause an error.

Not available on all platforms.

If an encoding (encoding name or encoding object) is specified as an optional argument, read string from pipe is tagged with the encoding specified. If the argument is a colon separated two encoding names “A:B”, the read string is converted from encoding A (external encoding) to encoding B (internal encoding), then tagged with B. If two optional arguments are specified, those must be encoding objects or encoding names, and the first one is the external encoding, and the second one is the internal encoding. If the external encoding and the internal encoding is specified, optional hash argument specify the conversion option.

In the example below, the two processes close the ends of the pipe that they are not using. This is not just a cosmetic nicety. The read end of a pipe will not generate an end of file condition if there are any writers with the pipe still open. In the case of the parent process, the rd.read will never return if it does not first issue a wr.close.

rd, wr = IO.pipe

if fork
  wr.close
  puts "Parent got: <#{rd.read}>"
  rd.close
  Process.wait
else
  rd.close
  puts "Sending message to parent"
  wr.write "Hi Dad"
  wr.close
end

produces:

Sending message to parent
Parent got: <Hi Dad>
 
               static VALUE
rb_io_s_pipe(int argc, VALUE *argv, VALUE klass)
{
    int pipes[2], state;
    VALUE r, w, args[3], v1, v2;
    VALUE opt;
    rb_io_t *fptr, *fptr2;
    struct io_encoding_set_args ies_args;
    int fmode = 0;
    VALUE ret;

    argc = rb_scan_args(argc, argv, "02:", &v1, &v2, &opt);
    if (rb_pipe(pipes) < 0)
        rb_sys_fail(0);

    args[0] = klass;
    args[1] = INT2NUM(pipes[0]);
    args[2] = INT2FIX(O_RDONLY);
    r = rb_protect(io_new_instance, (VALUE)args, &state);
    if (state) {
        close(pipes[0]);
        close(pipes[1]);
        rb_jump_tag(state);
    }
    GetOpenFile(r, fptr);

    ies_args.fptr = fptr;
    ies_args.v1 = v1;
    ies_args.v2 = v2;
    ies_args.opt = opt;
    rb_protect(io_encoding_set_v, (VALUE)&ies_args, &state);
    if (state) {
        close(pipes[1]);
        io_close(r);
        rb_jump_tag(state);
    }

    args[1] = INT2NUM(pipes[1]);
    args[2] = INT2FIX(O_WRONLY);
    w = rb_protect(io_new_instance, (VALUE)args, &state);
    if (state) {
        close(pipes[1]);
        if (!NIL_P(r)) rb_io_close(r);
        rb_jump_tag(state);
    }
    GetOpenFile(w, fptr2);
    rb_io_synchronized(fptr2);

    extract_binmode(opt, &fmode);

    if ((fmode & FMODE_BINMODE) && NIL_P(v1)) {
        rb_io_ascii8bit_binmode(r);
        rb_io_ascii8bit_binmode(w);
    }

#if DEFAULT_TEXTMODE
    if ((fptr->mode & FMODE_TEXTMODE) && (fmode & FMODE_BINMODE)) {
        fptr->mode &= ~FMODE_TEXTMODE;
        setmode(fptr->fd, O_BINARY);
    }
#if RUBY_CRLF_ENVIRONMENT
    if (fptr->encs.ecflags & ECONV_DEFAULT_NEWLINE_DECORATOR) {
        fptr->encs.ecflags |= ECONV_UNIVERSAL_NEWLINE_DECORATOR;
    }
#endif
#endif
    fptr->mode |= fmode;
#if DEFAULT_TEXTMODE
    if ((fptr2->mode & FMODE_TEXTMODE) && (fmode & FMODE_BINMODE)) {
        fptr2->mode &= ~FMODE_TEXTMODE;
        setmode(fptr2->fd, O_BINARY);
    }
#endif
    fptr2->mode |= fmode;

    ret = rb_assoc_new(r, w);
    if (rb_block_given_p()) {
        VALUE rw[2];
        rw[0] = r;
        rw[1] = w;
        return rb_ensure(rb_yield, ret, pipe_pair_close, (VALUE)rw);
    }
    return ret;
}
popen([env,] cmd, mode="r" [, opt]) → io click to toggle source
popen([env,] cmd, mode="r" [, opt]) {|io| block } → obj

Runs the specified command as a subprocess; the subprocess's standard input and output will be connected to the returned IO object.

The PID of the started process can be obtained by IO#pid method.

cmd is a string or an array as follows.

cmd:
  "-"                                      : fork
  commandline                              : command line string which is passed to a shell
  [env, cmdname, arg1, ..., opts]          : command name and zero or more arguments (no shell)
  [env, [cmdname, argv0], arg1, ..., opts] : command name, argv[0] and zero or more arguments (no shell)
(env and opts are optional.)

If cmd is a String “-'', then a new instance of Ruby is started as the subprocess.

If cmd is an Array of String, then it will be used as the subprocess's argv bypassing a shell. The array can contain a hash at first for environments and a hash at last for options similar to spawn.

The default mode for the new file object is “r'', but mode may be set to any of the modes listed in the description for class IO. The last argument opt qualifies mode.

# set IO encoding
IO.popen("nkf -e filename", :external_encoding=>"EUC-JP") {|nkf_io|
  euc_jp_string = nkf_io.read
}

# merge standard output and standard error using
# spawn option.  See the document of Kernel.spawn.
IO.popen(["ls", "/", :err=>[:child, :out]]) {|ls_io|
  ls_result_with_error = ls_io.read
}

# spawn options can be mixed with IO options
IO.popen(["ls", "/"], :err=>[:child, :out]) {|ls_io|
  ls_result_with_error = ls_io.read
}

Raises exceptions which IO.pipe and Kernel.spawn raise.

If a block is given, Ruby will run the command as a child connected to Ruby with a pipe. Ruby's end of the pipe will be passed as a parameter to the block. At the end of block, Ruby closes the pipe and sets $?. In this case IO.popen returns the value of the block.

If a block is given with a cmd of “-'', the block will be run in two separate processes: once in the parent, and once in a child. The parent process will be passed the pipe object as a parameter to the block, the child version of the block will be passed nil, and the child's standard in and standard out will be connected to the parent through the pipe. Not available on all platforms.

f = IO.popen("uname")
p f.readlines
f.close
puts "Parent is #{Process.pid}"
IO.popen("date") {|f| puts f.gets }
IO.popen("-") {|f| $stderr.puts "#{Process.pid} is here, f is #{f.inspect}"}
p $?
IO.popen(%w"sed -e s|^|<foo>| -e s&$&;zot;&", "r+") {|f|
  f.puts "bar"; f.close_write; puts f.gets
}

produces:

["Linux\n"]
Parent is 21346
Thu Jan 15 22:41:19 JST 2009
21346 is here, f is #<IO:fd 3>
21352 is here, f is nil
#<Process::Status: pid 21352 exit 0>
<foo>bar;zot;
 
               static VALUE
rb_io_s_popen(int argc, VALUE *argv, VALUE klass)
{
    VALUE pname, pmode = Qnil, opt = Qnil, env = Qnil;

    if (argc > 1 && !NIL_P(opt = rb_check_hash_type(argv[argc-1]))) --argc;
    if (argc > 1 && !NIL_P(env = rb_check_hash_type(argv[0]))) --argc, ++argv;
    switch (argc) {
      case 2:
        pmode = argv[1];
      case 1:
        pname = argv[0];
        break;
      default:
        {
            int ex = !NIL_P(opt);
            rb_error_arity(argc + ex, 1 + ex, 2 + ex);
        }
    }
    return popen_finish(rb_io_popen(pname, pmode, env, opt), klass);
}
read(name, [length [, offset]] [, opt]) → string click to toggle source
read(name, [length [, offset]] [, opt]) → string

Opens the file, optionally seeks to the given offset, then returns length bytes (defaulting to the rest of the file). read ensures the file is closed before returning.

If name starts with a pipe character ("|") and the receiver is the IO class, a subprocess is created in the same way as Kernel#open, and its output is returned. Consider to use File.read to disable the behavior of subprocess invocation.

Options ↑

The options hash accepts the following keys:

:encoding

string or encoding

Specifies the encoding of the read string. :encoding will be ignored if length is specified. See Encoding.aliases for possible encodings.

:mode

string or integer

Specifies the mode argument for open(). It must start with an “r”, otherwise it will cause an error. See IO.new for the list of possible modes.

:open_args

array

Specifies arguments for open() as an array. This key can not be used in combination with either :encoding or :mode.

Examples:

File.read("testfile")            #=> "This is line one\nThis is line two\nThis is line three\nAnd so on...\n"
File.read("testfile", 20)        #=> "This is line one\nThi"
File.read("testfile", 20, 10)    #=> "ne one\nThis is line "
File.read("binfile", mode: "rb") #=> "\xF7\x00\x00\x0E\x12"
IO.read("|ls -a")                #=> ".\n..\n"...

 
               static VALUE
rb_io_s_read(int argc, VALUE *argv, VALUE io)
{
    VALUE opt, offset;
    struct foreach_arg arg;

    argc = rb_scan_args(argc, argv, "13:", NULL, NULL, &offset, NULL, &opt);
    open_key_args(io, argc, argv, opt, &arg);
    if (NIL_P(arg.io)) return Qnil;
    if (!NIL_P(offset)) {
        struct seek_arg sarg;
        int state = 0;
        sarg.io = arg.io;
        sarg.offset = offset;
        sarg.mode = SEEK_SET;
        rb_protect(seek_before_access, (VALUE)&sarg, &state);
        if (state) {
            rb_io_close(arg.io);
            rb_jump_tag(state);
        }
        if (arg.argc == 2) arg.argc = 1;
    }
    return rb_ensure(io_s_read, (VALUE)&arg, rb_io_close, arg.io);
}
readlines(name, sep=$/ [, getline_args, open_args]) → array click to toggle source
readlines(name, limit [, getline_args, open_args]) → array
readlines(name, sep, limit [, getline_args, open_args]) → array
readlines(name, sep=$/ [, getline_args, open_args]) → array
readlines(name, limit [, getline_args, open_args]) → array
readlines(name, sep, limit [, getline_args, open_args]) → array

Reads the entire file specified by name as individual lines, and returns those lines in an array. Lines are separated by sep.

If name starts with a pipe character ("|") and the receiver is the IO class, a subprocess is created in the same way as Kernel#open, and its output is returned. Consider to use File.readlines to disable the behavior of subprocess invocation.

a = File.readlines("testfile")
a[0]   #=> "This is line one\n"

b = File.readlines("testfile", chomp: true)
b[0]   #=> "This is line one"

IO.readlines("|ls -a")     #=> [".\n", "..\n", ...]

If the last argument is a hash, it's the keyword argument to open.

Options for getline ↑

The options hash accepts the following keys:

:chomp

When the optional chomp keyword argument has a true value, \n, \r, and \r\n will be removed from the end of each line.

See also IO.read for details about name and open_args.

 
               static VALUE
rb_io_s_readlines(int argc, VALUE *argv, VALUE io)
{
    VALUE opt;
    struct foreach_arg arg;
    struct getline_arg garg;

    argc = rb_scan_args(argc, argv, "13:", NULL, NULL, NULL, NULL, &opt);
    extract_getline_args(argc-1, argv+1, &garg);
    open_key_args(io, argc, argv, opt, &arg);
    if (NIL_P(arg.io)) return Qnil;
    extract_getline_opts(opt, &garg);
    check_getline_args(&garg.rs, &garg.limit, garg.io = arg.io);
    return rb_ensure(io_s_readlines, (VALUE)&garg, rb_io_close, arg.io);
}
select(read_array [, write_array [, error_array [, timeout]]]) → array or nil click to toggle source

Calls select(2) system call. It monitors given arrays of IO objects, waits until one or more of IO objects are ready for reading, are ready for writing, and have pending exceptions respectively, and returns an array that contains arrays of those IO objects. It will return nil if optional timeout value is given and no IO object is ready in timeout seconds.

IO.select peeks the buffer of IO objects for testing readability. If the IO buffer is not empty, IO.select immediately notifies readability. This “peek” only happens for IO objects. It does not happen for IO-like objects such as OpenSSL::SSL::SSLSocket.

The best way to use IO.select is invoking it after nonblocking methods such as read_nonblock, write_nonblock, etc. The methods raise an exception which is extended by IO::WaitReadable or IO::WaitWritable. The modules notify how the caller should wait with IO.select. If IO::WaitReadable is raised, the caller should wait for reading. If IO::WaitWritable is raised, the caller should wait for writing.

So, blocking read (readpartial) can be emulated using read_nonblock and IO.select as follows:

begin
  result = io_like.read_nonblock(maxlen)
rescue IO::WaitReadable
  IO.select([io_like])
  retry
rescue IO::WaitWritable
  IO.select(nil, [io_like])
  retry
end

Especially, the combination of nonblocking methods and IO.select is preferred for IO like objects such as OpenSSL::SSL::SSLSocket. It has to_io method to return underlying IO object. IO.select calls to_io to obtain the file descriptor to wait.

This means that readability notified by IO.select doesn't mean readability from OpenSSL::SSL::SSLSocket object.

The most likely situation is that OpenSSL::SSL::SSLSocket buffers some data. IO.select doesn't see the buffer. So IO.select can block when OpenSSL::SSL::SSLSocket#readpartial doesn't block.

However, several more complicated situations exist.

SSL is a protocol which is sequence of records. The record consists of multiple bytes. So, the remote side of SSL sends a partial record, IO.select notifies readability but OpenSSL::SSL::SSLSocket cannot decrypt a byte and OpenSSL::SSL::SSLSocket#readpartial will block.

Also, the remote side can request SSL renegotiation which forces the local SSL engine to write some data. This means OpenSSL::SSL::SSLSocket#readpartial may invoke write system call and it can block. In such a situation, OpenSSL::SSL::SSLSocket#read_nonblock raises IO::WaitWritable instead of blocking. So, the caller should wait for ready for writability as above example.

The combination of nonblocking methods and IO.select is also useful for streams such as tty, pipe socket socket when multiple processes read from a stream.

Finally, Linux kernel developers don't guarantee that readability of select(2) means readability of following read(2) even for a single process. See select(2) manual on GNU/Linux system.

Invoking IO.select before IO#readpartial works well as usual. However it is not the best way to use IO.select.

The writability notified by select(2) doesn't show how many bytes are writable. IO#write method blocks until given whole string is written. So, IO#write(two or more bytes) can block after writability is notified by IO.select. IO#write_nonblock is required to avoid the blocking.

Blocking write (write) can be emulated using write_nonblock and IO.select as follows: IO::WaitReadable should also be rescued for SSL renegotiation in OpenSSL::SSL::SSLSocket.

while 0 < string.bytesize
  begin
    written = io_like.write_nonblock(string)
  rescue IO::WaitReadable
    IO.select([io_like])
    retry
  rescue IO::WaitWritable
    IO.select(nil, [io_like])
    retry
  end
  string = string.byteslice(written..-1)
end

Parameters ↑

read_array

an array of IO objects that wait until ready for read

write_array

an array of IO objects that wait until ready for write

error_array

an array of IO objects that wait for exceptions

timeout

a numeric value in second

Example ↑

rp, wp = IO.pipe
mesg = "ping "
100.times {
  # IO.select follows IO#read.  Not the best way to use IO.select.
  rs, ws, = IO.select([rp], [wp])
  if r = rs[0]
    ret = r.read(5)
    print ret
    case ret
    when /ping/
      mesg = "pong\n"
    when /pong/
      mesg = "ping "
    end
  end
  if w = ws[0]
    w.write(mesg)
  end
}

produces:

ping pong
ping pong
ping pong
(snipped)
ping

 
               static VALUE
rb_f_select(int argc, VALUE *argv, VALUE obj)
{
    VALUE timeout;
    struct select_args args;
    struct timeval timerec;
    int i;

    rb_scan_args(argc, argv, "13", &args.read, &args.write, &args.except, &timeout);
    if (NIL_P(timeout)) {
        args.timeout = 0;
    }
    else {
        timerec = rb_time_interval(timeout);
        args.timeout = &timerec;
    }

    for (i = 0; i < numberof(args.fdsets); ++i)
        rb_fd_init(&args.fdsets[i]);

    return rb_ensure(select_call, (VALUE)&args, select_end, (VALUE)&args);
}
sysopen(path, [mode, [perm]]) → integer click to toggle source

Opens the given path, returning the underlying file descriptor as a Integer.

IO.sysopen("testfile")   #=> 3

 
               static VALUE
rb_io_s_sysopen(int argc, VALUE *argv, VALUE _)
{
    VALUE fname, vmode, vperm;
    VALUE intmode;
    int oflags, fd;
    mode_t perm;

    rb_scan_args(argc, argv, "12", &fname, &vmode, &vperm);
    FilePathValue(fname);

    if (NIL_P(vmode))
        oflags = O_RDONLY;
    else if (!NIL_P(intmode = rb_check_to_integer(vmode, "to_int")))
        oflags = NUM2INT(intmode);
    else {
        SafeStringValue(vmode);
        oflags = rb_io_modestr_oflags(StringValueCStr(vmode));
    }
    if (NIL_P(vperm)) perm = 0666;
    else              perm = NUM2MODET(vperm);

    RB_GC_GUARD(fname) = rb_str_new4(fname);
    fd = rb_sysopen(fname, oflags, perm);
    return INT2NUM(fd);
}
try_convert(object) → new_io or nil click to toggle source

Attempts to convert object into an IO object via method to_io; returns the new IO object if successful, or nil otherwise:

IO.try_convert(STDOUT)   # => #<IO:<STDOUT>>
IO.try_convert(ARGF)     # => #<IO:<STDIN>>
IO.try_convert('STDOUT') # => nil

 
               static VALUE
rb_io_s_try_convert(VALUE dummy, VALUE io)
{
    return rb_io_check_io(io);
}
write(name, string [, offset]) → integer click to toggle source
write(name, string [, offset] [, opt]) → integer
write(name, string [, offset]) → integer
write(name, string [, offset] [, opt]) → integer

Opens the file, optionally seeks to the given offset, writes string, then returns the length written. write ensures the file is closed before returning. If offset is not given in write mode, the file is truncated. Otherwise, it is not truncated.

If name starts with a pipe character ("|") and the receiver is the IO class, a subprocess is created in the same way as Kernel#open, and its output is returned. Consider to use File.write to disable the behavior of subprocess invocation.

File.write("testfile", "0123456789", 20)  #=> 10
# File could contain:  "This is line one\nThi0123456789two\nThis is line three\nAnd so on...\n"
File.write("testfile", "0123456789")      #=> 10
# File would now read: "0123456789"
IO.write("|tr a-z A-Z", "abc")            #=> 3
# Prints "ABC" to the standard output

If the last argument is a hash, it specifies options for the internal open(). It accepts the following keys:

:encoding

string or encoding

Specifies the encoding of the read string. See Encoding.aliases for possible encodings.

:mode

string or integer

Specifies the mode argument for open(). It must start with “w”, “a”, or “r+”, otherwise it will cause an error. See IO.new for the list of possible modes.

:perm

integer

Specifies the perm argument for open().

:open_args

array

Specifies arguments for open() as an array. This key can not be used in combination with other keys.

See also IO.read for details about name and open_args.

 
               static VALUE
rb_io_s_write(int argc, VALUE *argv, VALUE io)
{
    return io_s_write(argc, argv, io, 0);
}

Public Instance Methods

self << object → self click to toggle source

Writes the given object to self, which must be opened for writing (see Modes); returns self; if object is not a string, it is converted via method to_s:

$stdout << 'Hello' << ', ' << 'World!' << "\n"
$stdout << 'foo' << :bar << 2 << "\n"

Output:

Hello, World!
foobar2
 
               VALUE
rb_io_addstr(VALUE io, VALUE str)
{
    rb_io_write(io, str);
    return io;
}
advise(advice, offset=0, len=0) → nil click to toggle source

Announce an intention to access data from the current file in a specific pattern. On platforms that do not support the posix_fadvise(2) system call, this method is a no-op.

advice is one of the following symbols:

:normal

No advice to give; the default assumption for an open file.

:sequential

The data will be accessed sequentially with lower offsets read before higher ones.

:random

The data will be accessed in random order.

:willneed

The data will be accessed in the near future.

:dontneed

The data will not be accessed in the near future.

:noreuse

The data will only be accessed once.

The semantics of a piece of advice are platform-dependent. See man 2 posix_fadvise for details.

“data” means the region of the current file that begins at offset and extends for len bytes. If len is 0, the region ends at the last byte of the file. By default, both offset and len are 0, meaning that the advice applies to the entire file.

If an error occurs, one of the following exceptions will be raised:

IOError

The IO stream is closed.

Errno::EBADF

The file descriptor of the current file is invalid.

Errno::EINVAL

An invalid value for advice was given.

Errno::ESPIPE

The file descriptor of the current file refers to a FIFO or pipe. (Linux raises Errno::EINVAL in this case).

TypeError

Either advice was not a Symbol, or one of the other arguments was not an Integer.

RangeError

One of the arguments given was too big/small.

This list is not exhaustive; other Errno

exceptions are also possible.

 
               static VALUE
rb_io_advise(int argc, VALUE *argv, VALUE io)
{
    VALUE advice, offset, len;
    off_t off, l;
    rb_io_t *fptr;

    rb_scan_args(argc, argv, "12", &advice, &offset, &len);
    advice_arg_check(advice);

    io = GetWriteIO(io);
    GetOpenFile(io, fptr);

    off = NIL_P(offset) ? 0 : NUM2OFFT(offset);
    l   = NIL_P(len)    ? 0 : NUM2OFFT(len);

#ifdef HAVE_POSIX_FADVISE
    return do_io_advise(fptr, advice, off, l);
#else
    ((void)off, (void)l);       /* Ignore all hint */
    return Qnil;
#endif
}
autoclose = bool → true or false click to toggle source

Sets auto-close flag.

f = open("/dev/null")
IO.for_fd(f.fileno)
# ...
f.gets # may cause Errno::EBADF

f = open("/dev/null")
IO.for_fd(f.fileno).autoclose = false
# ...
f.gets # won't cause Errno::EBADF

 
               static VALUE
rb_io_set_autoclose(VALUE io, VALUE autoclose)
{
    rb_io_t *fptr;
    GetOpenFile(io, fptr);
    if (!RTEST(autoclose))
        fptr->mode |= FMODE_PREP;
    else
        fptr->mode &= ~FMODE_PREP;
    return autoclose;
}
autoclose? → true or false click to toggle source

Returns true if the underlying file descriptor of ios will be closed automatically at its finalization, otherwise false.

 
               static VALUE
rb_io_autoclose_p(VALUE io)
{
    rb_io_t *fptr = RFILE(io)->fptr;
    rb_io_check_closed(fptr);
    return (fptr->mode & FMODE_PREP) ? Qfalse : Qtrue;
}
binmode → ios click to toggle source

Puts ios into binary mode. Once a stream is in binary mode, it cannot be reset to nonbinary mode.

  • newline conversion disabled

  • encoding conversion disabled

  • content is treated as ASCII-8BIT

 
               static VALUE
rb_io_binmode_m(VALUE io)
{
    VALUE write_io;

    rb_io_ascii8bit_binmode(io);

    write_io = GetWriteIO(io);
    if (write_io != io)
        rb_io_ascii8bit_binmode(write_io);
    return io;
}
binmode? → true or false click to toggle source

Returns true if ios is binmode.

 
               static VALUE
rb_io_binmode_p(VALUE io)
{
    rb_io_t *fptr;
    GetOpenFile(io, fptr);
    return RBOOL(fptr->mode & FMODE_BINMODE);
}
close → nil click to toggle source

Closes ios and flushes any pending writes to the operating system. The stream is unavailable for any further data operations; an IOError is raised if such an attempt is made. I/O streams are automatically closed when they are claimed by the garbage collector.

If ios is opened by IO.popen, close sets $?.

Calling this method on closed IO object is just ignored since Ruby 2.3.

 
               static VALUE
rb_io_close_m(VALUE io)
{
    rb_io_t *fptr = rb_io_get_fptr(io);
    if (fptr->fd < 0) {
        return Qnil;
    }
    rb_io_close(io);
    return Qnil;
}
close_on_exec = bool → true or false click to toggle source

Sets a close-on-exec flag.

f = open("/dev/null")
f.close_on_exec = true
system("cat", "/proc/self/fd/#{f.fileno}") # cat: /proc/self/fd/3: No such file or directory
f.closed?                #=> false

Ruby sets close-on-exec flags of all file descriptors by default since Ruby 2.0.0. So you don't need to set by yourself. Also, unsetting a close-on-exec flag can cause file descriptor leak if another thread use fork() and exec() (via system() method for example). If you really needs file descriptor inheritance to child process, use spawn()'s argument such as fd=>fd.

 
               static VALUE
rb_io_set_close_on_exec(VALUE io, VALUE arg)
{
    int flag = RTEST(arg) ? FD_CLOEXEC : 0;
    rb_io_t *fptr;
    VALUE write_io;
    int fd, ret;

    write_io = GetWriteIO(io);
    if (io != write_io) {
        GetOpenFile(write_io, fptr);
        if (fptr && 0 <= (fd = fptr->fd)) {
            if ((ret = fcntl(fptr->fd, F_GETFD)) == -1) rb_sys_fail_path(fptr->pathv);
            if ((ret & FD_CLOEXEC) != flag) {
                ret = (ret & ~FD_CLOEXEC) | flag;
                ret = fcntl(fd, F_SETFD, ret);
                if (ret != 0) rb_sys_fail_path(fptr->pathv);
            }
        }

    }

    GetOpenFile(io, fptr);
    if (fptr && 0 <= (fd = fptr->fd)) {
        if ((ret = fcntl(fd, F_GETFD)) == -1) rb_sys_fail_path(fptr->pathv);
        if ((ret & FD_CLOEXEC) != flag) {
            ret = (ret & ~FD_CLOEXEC) | flag;
            ret = fcntl(fd, F_SETFD, ret);
            if (ret != 0) rb_sys_fail_path(fptr->pathv);
        }
    }
    return Qnil;
}
close_on_exec? → true or false click to toggle source

Returns true if ios will be closed on exec.

f = open("/dev/null")
f.close_on_exec?                 #=> false
f.close_on_exec = true
f.close_on_exec?                 #=> true
f.close_on_exec = false
f.close_on_exec?                 #=> false

 
               static VALUE
rb_io_close_on_exec_p(VALUE io)
{
    rb_io_t *fptr;
    VALUE write_io;
    int fd, ret;

    write_io = GetWriteIO(io);
    if (io != write_io) {
        GetOpenFile(write_io, fptr);
        if (fptr && 0 <= (fd = fptr->fd)) {
            if ((ret = fcntl(fd, F_GETFD)) == -1) rb_sys_fail_path(fptr->pathv);
            if (!(ret & FD_CLOEXEC)) return Qfalse;
        }
    }

    GetOpenFile(io, fptr);
    if (fptr && 0 <= (fd = fptr->fd)) {
        if ((ret = fcntl(fd, F_GETFD)) == -1) rb_sys_fail_path(fptr->pathv);
        if (!(ret & FD_CLOEXEC)) return Qfalse;
    }
    return Qtrue;
}
close_read → nil click to toggle source

Closes the read end of a duplex I/O stream (i.e., one that contains both a read and a write stream, such as a pipe). Will raise an IOError if the stream is not duplexed.

f = IO.popen("/bin/sh","r+")
f.close_read
f.readlines

produces:

prog.rb:3:in `readlines': not opened for reading (IOError)
 from prog.rb:3

Calling this method on closed IO object is just ignored since Ruby 2.3.

 
               static VALUE
rb_io_close_read(VALUE io)
{
    rb_io_t *fptr;
    VALUE write_io;

    fptr = rb_io_get_fptr(rb_io_taint_check(io));
    if (fptr->fd < 0) return Qnil;
    if (is_socket(fptr->fd, fptr->pathv)) {
#ifndef SHUT_RD
# define SHUT_RD 0
#endif
        if (shutdown(fptr->fd, SHUT_RD) < 0)
            rb_sys_fail_path(fptr->pathv);
        fptr->mode &= ~FMODE_READABLE;
        if (!(fptr->mode & FMODE_WRITABLE))
            return rb_io_close(io);
        return Qnil;
    }

    write_io = GetWriteIO(io);
    if (io != write_io) {
        rb_io_t *wfptr;
        wfptr = rb_io_get_fptr(rb_io_taint_check(write_io));
        wfptr->pid = fptr->pid;
        fptr->pid = 0;
        RFILE(io)->fptr = wfptr;
        /* bind to write_io temporarily to get rid of memory/fd leak */
        fptr->tied_io_for_writing = 0;
        RFILE(write_io)->fptr = fptr;
        rb_io_fptr_cleanup(fptr, FALSE);
        /* should not finalize fptr because another thread may be reading it */
        return Qnil;
    }

    if ((fptr->mode & (FMODE_DUPLEX|FMODE_WRITABLE)) == FMODE_WRITABLE) {
        rb_raise(rb_eIOError, "closing non-duplex IO for reading");
    }
    return rb_io_close(io);
}
close_write → nil click to toggle source

Closes the write end of a duplex I/O stream (i.e., one that contains both a read and a write stream, such as a pipe). Will raise an IOError if the stream is not duplexed.

f = IO.popen("/bin/sh","r+")
f.close_write
f.print "nowhere"

produces:

prog.rb:3:in `write': not opened for writing (IOError)
 from prog.rb:3:in `print'
 from prog.rb:3

Calling this method on closed IO object is just ignored since Ruby 2.3.

 
               static VALUE
rb_io_close_write(VALUE io)
{
    rb_io_t *fptr;
    VALUE write_io;

    write_io = GetWriteIO(io);
    fptr = rb_io_get_fptr(rb_io_taint_check(write_io));
    if (fptr->fd < 0) return Qnil;
    if (is_socket(fptr->fd, fptr->pathv)) {
#ifndef SHUT_WR
# define SHUT_WR 1
#endif
        if (shutdown(fptr->fd, SHUT_WR) < 0)
            rb_sys_fail_path(fptr->pathv);
        fptr->mode &= ~FMODE_WRITABLE;
        if (!(fptr->mode & FMODE_READABLE))
            return rb_io_close(write_io);
        return Qnil;
    }

    if ((fptr->mode & (FMODE_DUPLEX|FMODE_READABLE)) == FMODE_READABLE) {
        rb_raise(rb_eIOError, "closing non-duplex IO for writing");
    }

    if (io != write_io) {
        fptr = rb_io_get_fptr(rb_io_taint_check(io));
        fptr->tied_io_for_writing = 0;
    }
    rb_io_close(write_io);
    return Qnil;
}
closed? → true or false click to toggle source

Returns true if ios is completely closed (for duplex streams, both reader and writer), false otherwise.

f = File.new("testfile")
f.close         #=> nil
f.closed?       #=> true
f = IO.popen("/bin/sh","r+")
f.close_write   #=> nil
f.closed?       #=> false
f.close_read    #=> nil
f.closed?       #=> true

 
               static VALUE
rb_io_closed(VALUE io)
{
    rb_io_t *fptr;
    VALUE write_io;
    rb_io_t *write_fptr;

    write_io = GetWriteIO(io);
    if (io != write_io) {
        write_fptr = RFILE(write_io)->fptr;
        if (write_fptr && 0 <= write_fptr->fd) {
            return Qfalse;
        }
    }

    fptr = rb_io_get_fptr(io);
    return RBOOL(0 > fptr->fd);
}
each(sep=$/ [, getline_args]) {|line| block } → ios click to toggle source
each(limit [, getline_args]) {|line| block } → ios
each(sep, limit [, getline_args]) {|line| block } → ios
each(...) → an_enumerator
each_line(sep=$/ [, getline_args]) {|line| block } → ios
each_line(limit [, getline_args]) {|line| block } → ios
each_line(sep, limit [, getline_args]) {|line| block } → ios
each_line(...) → an_enumerator

Executes the block for every line in ios, where lines are separated by sep. ios must be opened for reading or an IOError will be raised.

If no block is given, an enumerator is returned instead.

f = File.new("testfile")
f.each {|line| puts "#{f.lineno}: #{line}" }

produces:

1: This is line one
2: This is line two
3: This is line three
4: And so on...

See IO.readlines for details about getline_args.

 
               static VALUE
rb_io_each_line(int argc, VALUE *argv, VALUE io)
{
    VALUE str;
    struct getline_arg args;

    RETURN_ENUMERATOR(io, argc, argv);
    prepare_getline_args(argc, argv, &args, io);
    if (args.limit == 0)
        rb_raise(rb_eArgError, "invalid limit: 0 for each_line");
    while (!NIL_P(str = rb_io_getline_1(args.rs, args.limit, args.chomp, io))) {
        rb_yield(str);
    }
    return io;
}
each_byte {|byte| block } → ios click to toggle source
each_byte → an_enumerator

Calls the given block once for each byte (0..255) in ios, passing the byte as an argument. The stream must be opened for reading or an IOError will be raised.

If no block is given, an enumerator is returned instead.

f = File.new("testfile")
checksum = 0
f.each_byte {|x| checksum ^= x }   #=> #<File:testfile>
checksum                           #=> 12

 
               static VALUE
rb_io_each_byte(VALUE io)
{
    rb_io_t *fptr;

    RETURN_ENUMERATOR(io, 0, 0);
    GetOpenFile(io, fptr);

    do {
        while (fptr->rbuf.len > 0) {
            char *p = fptr->rbuf.ptr + fptr->rbuf.off++;
            fptr->rbuf.len--;
            rb_yield(INT2FIX(*p & 0xff));
            rb_io_check_byte_readable(fptr);
            errno = 0;
        }
        READ_CHECK(fptr);
    } while (io_fillbuf(fptr) >= 0);
    return io;
}
each_char {|c| block } → ios click to toggle source
each_char → an_enumerator

Calls the given block once for each character in ios, passing the character as an argument. The stream must be opened for reading or an IOError will be raised.

If no block is given, an enumerator is returned instead.

f = File.new("testfile")
f.each_char {|c| print c, ' ' }   #=> #<File:testfile>

 
               static VALUE
rb_io_each_char(VALUE io)
{
    rb_io_t *fptr;
    rb_encoding *enc;
    VALUE c;

    RETURN_ENUMERATOR(io, 0, 0);
    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);

    enc = io_input_encoding(fptr);
    READ_CHECK(fptr);
    while (!NIL_P(c = io_getc(fptr, enc))) {
        rb_yield(c);
    }
    return io;
}
each_codepoint {|c| block } → ios click to toggle source
each_codepoint → an_enumerator

Passes the Integer ordinal of each character in ios, passing the codepoint as an argument. The stream must be opened for reading or an IOError will be raised.

If no block is given, an enumerator is returned instead.

 
               static VALUE
rb_io_each_codepoint(VALUE io)
{
    rb_io_t *fptr;
    rb_encoding *enc;
    unsigned int c;
    int r, n;

    RETURN_ENUMERATOR(io, 0, 0);
    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);

    READ_CHECK(fptr);
    if (NEED_READCONV(fptr)) {
        SET_BINARY_MODE(fptr);
        r = 1;         /* no invalid char yet */
        for (;;) {
            make_readconv(fptr, 0);
            for (;;) {
                if (fptr->cbuf.len) {
                    if (fptr->encs.enc)
                        r = rb_enc_precise_mbclen(fptr->cbuf.ptr+fptr->cbuf.off,
                                                  fptr->cbuf.ptr+fptr->cbuf.off+fptr->cbuf.len,
                                                  fptr->encs.enc);
                    else
                        r = ONIGENC_CONSTRUCT_MBCLEN_CHARFOUND(1);
                    if (!MBCLEN_NEEDMORE_P(r))
                        break;
                    if (fptr->cbuf.len == fptr->cbuf.capa) {
                        rb_raise(rb_eIOError, "too long character");
                    }
                }
                if (more_char(fptr) == MORE_CHAR_FINISHED) {
                    clear_readconv(fptr);
                    if (!MBCLEN_CHARFOUND_P(r)) {
                        enc = fptr->encs.enc;
                        goto invalid;
                    }
                    return io;
                }
            }
            if (MBCLEN_INVALID_P(r)) {
                enc = fptr->encs.enc;
                goto invalid;
            }
            n = MBCLEN_CHARFOUND_LEN(r);
            if (fptr->encs.enc) {
                c = rb_enc_codepoint(fptr->cbuf.ptr+fptr->cbuf.off,
                                     fptr->cbuf.ptr+fptr->cbuf.off+fptr->cbuf.len,
                                     fptr->encs.enc);
            }
            else {
                c = (unsigned char)fptr->cbuf.ptr[fptr->cbuf.off];
            }
            fptr->cbuf.off += n;
            fptr->cbuf.len -= n;
            rb_yield(UINT2NUM(c));
            rb_io_check_byte_readable(fptr);
        }
    }
    NEED_NEWLINE_DECORATOR_ON_READ_CHECK(fptr);
    enc = io_input_encoding(fptr);
    while (io_fillbuf(fptr) >= 0) {
        r = rb_enc_precise_mbclen(fptr->rbuf.ptr+fptr->rbuf.off,
                                  fptr->rbuf.ptr+fptr->rbuf.off+fptr->rbuf.len, enc);
        if (MBCLEN_CHARFOUND_P(r) &&
            (n = MBCLEN_CHARFOUND_LEN(r)) <= fptr->rbuf.len) {
            c = rb_enc_codepoint(fptr->rbuf.ptr+fptr->rbuf.off,
                                 fptr->rbuf.ptr+fptr->rbuf.off+fptr->rbuf.len, enc);
            fptr->rbuf.off += n;
            fptr->rbuf.len -= n;
            rb_yield(UINT2NUM(c));
        }
        else if (MBCLEN_INVALID_P(r)) {
            goto invalid;
        }
        else if (MBCLEN_NEEDMORE_P(r)) {
            char cbuf[8], *p = cbuf;
            int more = MBCLEN_NEEDMORE_LEN(r);
            if (more > numberof(cbuf)) goto invalid;
            more += n = fptr->rbuf.len;
            if (more > numberof(cbuf)) goto invalid;
            while ((n = (int)read_buffered_data(p, more, fptr)) > 0 &&
                   (p += n, (more -= n) > 0)) {
                if (io_fillbuf(fptr) < 0) goto invalid;
                if ((n = fptr->rbuf.len) > more) n = more;
            }
            r = rb_enc_precise_mbclen(cbuf, p, enc);
            if (!MBCLEN_CHARFOUND_P(r)) goto invalid;
            c = rb_enc_codepoint(cbuf, p, enc);
            rb_yield(UINT2NUM(c));
        }
        else {
            continue;
        }
        rb_io_check_byte_readable(fptr);
    }
    return io;

  invalid:
    rb_raise(rb_eArgError, "invalid byte sequence in %s", rb_enc_name(enc));
    UNREACHABLE_RETURN(Qundef);
}
each_line(sep=$/ [, getline_args]) {|line| block } → ios click to toggle source
each_line(limit [, getline_args]) {|line| block } → ios
each_line(sep, limit [, getline_args]) {|line| block } → ios
each_line(...) → an_enumerator

Executes the block for every line in ios, where lines are separated by sep. ios must be opened for reading or an IOError will be raised.

If no block is given, an enumerator is returned instead.

f = File.new("testfile")
f.each {|line| puts "#{f.lineno}: #{line}" }

produces:

1: This is line one
2: This is line two
3: This is line three
4: And so on...

See IO.readlines for details about getline_args.

 
               static VALUE
rb_io_each_line(int argc, VALUE *argv, VALUE io)
{
    VALUE str;
    struct getline_arg args;

    RETURN_ENUMERATOR(io, argc, argv);
    prepare_getline_args(argc, argv, &args, io);
    if (args.limit == 0)
        rb_raise(rb_eArgError, "invalid limit: 0 for each_line");
    while (!NIL_P(str = rb_io_getline_1(args.rs, args.limit, args.chomp, io))) {
        rb_yield(str);
    }
    return io;
}
eof → true or false click to toggle source

Returns true if the stream is positioned at its end, false otherwise; see Position:

f = File.open('t.txt')
f.eof           # => false
f.seek(0, :END) # => 0
f.eof           # => true

Raises an exception unless the stream is opened for reading; see Mode.

If self is a stream such as pipe or socket, this method blocks until the other end sends some data or closes it:

r, w = IO.pipe
Thread.new { sleep 1; w.close }
r.eof? # => true # After 1-second wait.

r, w = IO.pipe
Thread.new { sleep 1; w.puts "a" }
r.eof?  # => false # After 1-second wait.

r, w = IO.pipe
r.eof?  # blocks forever

Note that this method reads data to the input byte buffer. So IO#sysread may not behave as you intend with IO#eof?, unless you call IO#rewind first (which is not available for some streams).

I#eof? is an alias for IO#eof.

 
               VALUE
rb_io_eof(VALUE io)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);

    if (READ_CHAR_PENDING(fptr)) return Qfalse;
    if (READ_DATA_PENDING(fptr)) return Qfalse;
    READ_CHECK(fptr);
#if RUBY_CRLF_ENVIRONMENT
    if (!NEED_READCONV(fptr) && NEED_NEWLINE_DECORATOR_ON_READ(fptr)) {
        return RBOOL(eof(fptr->fd));;
    }
#endif
    return RBOOL(io_fillbuf(fptr) < 0);
}
eof → true or false click to toggle source

Returns true if the stream is positioned at its end, false otherwise; see Position:

f = File.open('t.txt')
f.eof           # => false
f.seek(0, :END) # => 0
f.eof           # => true

Raises an exception unless the stream is opened for reading; see Mode.

If self is a stream such as pipe or socket, this method blocks until the other end sends some data or closes it:

r, w = IO.pipe
Thread.new { sleep 1; w.close }
r.eof? # => true # After 1-second wait.

r, w = IO.pipe
Thread.new { sleep 1; w.puts "a" }
r.eof?  # => false # After 1-second wait.

r, w = IO.pipe
r.eof?  # blocks forever

Note that this method reads data to the input byte buffer. So IO#sysread may not behave as you intend with IO#eof?, unless you call IO#rewind first (which is not available for some streams).

I#eof? is an alias for IO#eof.

 
               VALUE
rb_io_eof(VALUE io)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);

    if (READ_CHAR_PENDING(fptr)) return Qfalse;
    if (READ_DATA_PENDING(fptr)) return Qfalse;
    READ_CHECK(fptr);
#if RUBY_CRLF_ENVIRONMENT
    if (!NEED_READCONV(fptr) && NEED_NEWLINE_DECORATOR_ON_READ(fptr)) {
        return RBOOL(eof(fptr->fd));;
    }
#endif
    return RBOOL(io_fillbuf(fptr) < 0);
}
external_encoding → encoding click to toggle source

Returns the Encoding object that represents the encoding of the file. If io is in write mode and no encoding is specified, returns nil.

 
               static VALUE
rb_io_external_encoding(VALUE io)
{
    rb_io_t *fptr = RFILE(rb_io_taint_check(io))->fptr;

    if (fptr->encs.enc2) {
        return rb_enc_from_encoding(fptr->encs.enc2);
    }
    if (fptr->mode & FMODE_WRITABLE) {
        if (fptr->encs.enc)
            return rb_enc_from_encoding(fptr->encs.enc);
        return Qnil;
    }
    return rb_enc_from_encoding(io_read_encoding(fptr));
}
fcntl(integer_cmd, arg) → integer click to toggle source

Provides a mechanism for issuing low-level commands to control or query file-oriented I/O streams. Arguments and results are platform dependent. If arg is a number, its value is passed directly. If it is a string, it is interpreted as a binary sequence of bytes (Array#pack might be a useful way to build this string). On Unix platforms, see fcntl(2) for details. Not implemented on all platforms.

 
               static VALUE
rb_io_fcntl(int argc, VALUE *argv, VALUE io)
{
    VALUE req, arg;

    rb_scan_args(argc, argv, "11", &req, &arg);
    return rb_fcntl(io, req, arg);
}
fdatasync → 0 click to toggle source

Immediately writes to disk all data buffered in the stream, via the operating system's: fdatasync(2), if supported, otherwise via fsync(2), if supported; otherwise raises an exception.

 
               static VALUE
rb_io_fdatasync(VALUE io)
{
    rb_io_t *fptr;

    io = GetWriteIO(io);
    GetOpenFile(io, fptr);

    if (io_fflush(fptr) < 0)
        rb_sys_fail_on_write(fptr);

    if ((int)rb_thread_io_blocking_region(nogvl_fdatasync, fptr, fptr->fd) == 0)
        return INT2FIX(0);

    /* fall back */
    return rb_io_fsync(io);
}
fileno → integer click to toggle source

Returns the integer file descriptor for the stream:

$stdin.fileno             # => 0
$stdout.fileno            # => 1
$stderr.fileno            # => 2
File.open('t.txt').fileno # => 10

IO#to_i is an alias for IO#fileno.

 
               static VALUE
rb_io_fileno(VALUE io)
{
    rb_io_t *fptr = RFILE(io)->fptr;
    int fd;

    rb_io_check_closed(fptr);
    fd = fptr->fd;
    return INT2FIX(fd);
}
Also aliased as: to_i
flush → self click to toggle source

Flushes data buffered in self to the operating system (but does not necessarily flush data buffered in the operating system):

$stdout.print 'no newline' # Not necessarily flushed.
$stdout.flush              # Flushed.

 
               VALUE
rb_io_flush(VALUE io)
{
    return rb_io_flush_raw(io, 1);
}
fsync → 0 click to toggle source

Immediately writes to disk all data buffered in the stream, via the operating system's fsync(2).

Note this difference:

  • IO#sync=: Ensures that data is flushed from the stream's internal buffers, but does not guarantee that the operating system actually writes the data to disk.

  • IO#fsync: Ensures both that data is flushed from internal buffers, and that data is written to disk.

Raises an exception if the operating system does not support fsync(2).

 
               static VALUE
rb_io_fsync(VALUE io)
{
    rb_io_t *fptr;

    io = GetWriteIO(io);
    GetOpenFile(io, fptr);

    if (io_fflush(fptr) < 0)
        rb_sys_fail_on_write(fptr);
    if ((int)rb_thread_io_blocking_region(nogvl_fsync, fptr, fptr->fd) < 0)
        rb_sys_fail_path(fptr->pathv);
    return INT2FIX(0);
}
getbyte → integer or nil click to toggle source

Gets the next 8-bit byte (0..255) from ios. Returns nil if called at end of file.

f = File.new("testfile")
f.getbyte   #=> 84
f.getbyte   #=> 104

 
               VALUE
rb_io_getbyte(VALUE io)
{
    rb_io_t *fptr;
    int c;

    GetOpenFile(io, fptr);
    rb_io_check_byte_readable(fptr);
    READ_CHECK(fptr);
    VALUE r_stdout = rb_ractor_stdout();
    if (fptr->fd == 0 && (fptr->mode & FMODE_TTY) && RB_TYPE_P(r_stdout, T_FILE)) {
        rb_io_t *ofp;
        GetOpenFile(r_stdout, ofp);
        if (ofp->mode & FMODE_TTY) {
            rb_io_flush(r_stdout);
        }
    }
    if (io_fillbuf(fptr) < 0) {
        return Qnil;
    }
    fptr->rbuf.off++;
    fptr->rbuf.len--;
    c = (unsigned char)fptr->rbuf.ptr[fptr->rbuf.off-1];
    return INT2FIX(c & 0xff);
}
getc → string or nil click to toggle source

Reads a one-character string from ios. Returns nil if called at end of file.

f = File.new("testfile")
f.getc   #=> "h"
f.getc   #=> "e"

 
               static VALUE
rb_io_getc(VALUE io)
{
    rb_io_t *fptr;
    rb_encoding *enc;

    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);

    enc = io_input_encoding(fptr);
    READ_CHECK(fptr);
    return io_getc(fptr, enc);
}
gets(sep = $/, **getline_opts) → string or nil click to toggle source
gets(limit, **getline_opts) → string or nil
gets(sep, limit, **getline_opts) → string or nil

Reads and returns data from the stream; assigns the return value to $_.

With no arguments given, returns the next line as determined by line separator $/, or nil if none:

f = File.open('t.txt')
f.gets # => "This is line one.\n"
$_     # => "This is line one.\n"
f.gets # => "This is the second line.\n"
f.gets # => "This is the third line.\n"
f.gets # => nil

With string argument sep given, but not argument limit, returns the next line as determined by line separator sep, or nil if none:

f = File.open('t.txt')
f.gets(' is') # => "This is"
f.gets(' is') # => " line one.\nThis is"
f.gets(' is') # => " the second line.\nThis is"
f.gets(' is') # => " the third line.\n"
f.gets(' is') # => nil

Note two special values for sep:

  • nil: The entire stream is read and returned.

  • '' (empty string): The next “paragraph” is read and returned, the paragraph separator being two successive line separators.

With integer argument limit given, returns up to limit+1 bytes:

# Text with 1-byte characters.
File.open('t.txt') {|f| f.gets(1) } # => "T"
File.open('t.txt') {|f| f.gets(2) } # => "Th"
File.open('t.txt') {|f| f.gets(3) } # => "Thi"
File.open('t.txt') {|f| f.gets(4) } # => "This"
# No more than one line.
File.open('t.txt') {|f| f.gets(17) } # => "This is line one."
File.open('t.txt') {|f| f.gets(18) } # => "This is line one.\n"
File.open('t.txt') {|f| f.gets(19) } # => "This is line one.\n"

# Text with 2-byte characters, which will not be split.
File.open('t.rus') {|f| f.gets(1).size } # => 1
File.open('t.rus') {|f| f.gets(2).size } # => 1
File.open('t.rus') {|f| f.gets(3).size } # => 2
File.open('t.rus') {|f| f.gets(4).size } # => 2

With arguments sep and limit, combines the two behaviors above:

  • Returns the next line as determined by line separator sep, or nil if none.

  • But returns no more than limit+1 bytes.

For all forms above, trailing optional keyword arguments may be given; see Getline Options:

f = File.open('t.txt')
# Chomp the lines.
f.gets(chomp: true) # => "This is line one."
f.gets(chomp: true) # => "This is the second line."
f.gets(chomp: true) # => "This is the third line."
f.gets(chomp: true) # => nil

 
               static VALUE
rb_io_gets_m(int argc, VALUE *argv, VALUE io)
{
    VALUE str;

    str = rb_io_getline(argc, argv, io);
    rb_lastline_set(str);

    return str;
}
inspect → string click to toggle source

Returns a string representation of self:

f = File.open('t.txt')
f.inspect # => "#<File:t.txt>"

 
               static VALUE
rb_io_inspect(VALUE obj)
{
    rb_io_t *fptr;
    VALUE result;
    static const char closed[] = " (closed)";

    fptr = RFILE(obj)->fptr;
    if (!fptr) return rb_any_to_s(obj);
    result = rb_str_new_cstr("#<");
    rb_str_append(result, rb_class_name(CLASS_OF(obj)));
    rb_str_cat2(result, ":");
    if (NIL_P(fptr->pathv)) {
        if (fptr->fd < 0) {
            rb_str_cat(result, closed+1, strlen(closed)-1);
        }
        else {
            rb_str_catf(result, "fd %d", fptr->fd);
        }
    }
    else {
        rb_str_append(result, fptr->pathv);
        if (fptr->fd < 0) {
            rb_str_cat(result, closed, strlen(closed));
        }
    }
    return rb_str_cat2(result, ">");
}
internal_encoding → encoding click to toggle source

Returns the Encoding of the internal string if conversion is specified. Otherwise returns nil.

 
               static VALUE
rb_io_internal_encoding(VALUE io)
{
    rb_io_t *fptr = RFILE(rb_io_taint_check(io))->fptr;

    if (!fptr->encs.enc2) return Qnil;
    return rb_enc_from_encoding(io_read_encoding(fptr));
}
ioctl(integer_cmd, arg) → integer click to toggle source

Provides a mechanism for issuing low-level commands to control or query I/O devices. Arguments and results are platform dependent. If arg is a number, its value is passed directly. If it is a string, it is interpreted as a binary sequence of bytes. On Unix platforms, see ioctl(2) for details. Not implemented on all platforms.

 
               static VALUE
rb_io_ioctl(int argc, VALUE *argv, VALUE io)
{
    VALUE req, arg;

    rb_scan_args(argc, argv, "11", &req, &arg);
    return rb_ioctl(io, req, arg);
}
isatty → true or false click to toggle source

Returns true if ios is associated with a terminal device (tty), false otherwise.

File.new("testfile").isatty   #=> false
File.new("/dev/tty").isatty   #=> true

 
               static VALUE
rb_io_isatty(VALUE io)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    return RBOOL(isatty(fptr->fd) != 0);
}
lineno → integer click to toggle source

Returns the current line number in ios. The stream must be opened for reading. lineno counts the number of times gets is called rather than the number of newlines encountered. The two values will differ if gets is called with a separator other than newline.

Methods that use $/ like each, lines and readline will also increment lineno.

See also the $. variable.

f = File.new("testfile")
f.lineno   #=> 0
f.gets     #=> "This is line one\n"
f.lineno   #=> 1
f.gets     #=> "This is line two\n"
f.lineno   #=> 2

 
               static VALUE
rb_io_lineno(VALUE io)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);
    return INT2NUM(fptr->lineno);
}
lineno = integer → integer click to toggle source

Manually sets the current line number to the given value. $. is updated only on the next read.

f = File.new("testfile")
f.gets                     #=> "This is line one\n"
$.                         #=> 1
f.lineno = 1000
f.lineno                   #=> 1000
$.                         #=> 1         # lineno of last read
f.gets                     #=> "This is line two\n"
$.                         #=> 1001      # lineno of last read

 
               static VALUE
rb_io_set_lineno(VALUE io, VALUE lineno)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);
    fptr->lineno = NUM2INT(lineno);
    return lineno;
}
pid → integer or nil click to toggle source

Returns the process ID of a child process associated with the stream, which will have been set by IO#popen, or nil if the stream was not created by IO#popen:

pipe = IO.popen("-")
if pipe
  $stderr.puts "In parent, child pid is #{pipe.pid}"
else
  $stderr.puts "In child, pid is #{$$}"
end

Output:

In child, pid is 26209
In parent, child pid is 26209
 
               static VALUE
rb_io_pid(VALUE io)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    if (!fptr->pid)
        return Qnil;
    return PIDT2NUM(fptr->pid);
}
tell → integer click to toggle source

Returns the current position (in bytes) in self (see Position):

f = File.new('t.txt')
f.tell     # => 0
f.readline # => "This is line one.\n"
f.tell     # => 19

Related: IO#pos=, IO#seek.

IO#pos is an alias for IO#tell.

 
               static VALUE
rb_io_tell(VALUE io)
{
    rb_io_t *fptr;
    off_t pos;

    GetOpenFile(io, fptr);
    pos = io_tell(fptr);
    if (pos < 0 && errno) rb_sys_fail_path(fptr->pathv);
    pos -= fptr->rbuf.len;
    return OFFT2NUM(pos);
}
pos = new_position → new_position click to toggle source

Seeks to the given new_position (in bytes); see Position:

f = File.open('t.txt')
f.tell     # => 0
f.pos = 20 # => 20
f.tell     # => 20

Related: IO#seek, IO#tell.

 
               static VALUE
rb_io_set_pos(VALUE io, VALUE offset)
{
    rb_io_t *fptr;
    off_t pos;

    pos = NUM2OFFT(offset);
    GetOpenFile(io, fptr);
    pos = io_seek(fptr, pos, SEEK_SET);
    if (pos < 0 && errno) rb_sys_fail_path(fptr->pathv);

    return OFFT2NUM(pos);
}
pread(maxlen, offset[, outbuf]) → string click to toggle source

Reads maxlen bytes from ios using the pread system call and returns them as a string without modifying the underlying descriptor offset. This is advantageous compared to combining IO#seek and IO#read in that it is atomic, allowing multiple threads/process to share the same IO object for reading the file at various locations. This bypasses any userspace buffering of the IO layer. If the optional outbuf argument is present, it must reference a String, which will receive the data. Raises SystemCallError on error, EOFError at end of file and NotImplementedError if platform does not implement the system call.

File.write("testfile", "This is line one\nThis is line two\n")
File.open("testfile") do |f|
  p f.read           # => "This is line one\nThis is line two\n"
  p f.pread(12, 0)   # => "This is line"
  p f.pread(9, 8)    # => "line one\n"
end

 
               static VALUE
rb_io_pread(int argc, VALUE *argv, VALUE io)
{
    VALUE len, offset, str;
    rb_io_t *fptr;
    ssize_t n;
    struct prdwr_internal_arg arg;
    int shrinkable;

    rb_scan_args(argc, argv, "21", &len, &offset, &str);
    arg.count = NUM2SIZET(len);
    arg.offset = NUM2OFFT(offset);

    shrinkable = io_setstrbuf(&str, (long)arg.count);
    if (arg.count == 0) return str;
    arg.buf = RSTRING_PTR(str);

    GetOpenFile(io, fptr);
    rb_io_check_byte_readable(fptr);

    arg.fd = fptr->fd;
    rb_io_check_closed(fptr);

    rb_str_locktmp(str);
    n = (ssize_t)rb_ensure(pread_internal_call, (VALUE)&arg, rb_str_unlocktmp, str);

    if (n < 0) {
        rb_sys_fail_path(fptr->pathv);
    }
    io_set_read_length(str, n, shrinkable);
    if (n == 0 && arg.count > 0) {
        rb_eof_error();
    }

    return str;
}
print → nil click to toggle source
print(obj, ...) → nil

Writes the given object(s) to ios. Returns nil.

The stream must be opened for writing. Each given object that isn't a string will be converted by calling its to_s method. When called without arguments, prints the contents of $_.

If the output field separator ($,) is not nil, it is inserted between objects. If the output record separator ($\) is not nil, it is appended to the output.

$stdout.print("This is ", 100, " percent.\n")

produces:

This is 100 percent.
printf(format_string [, obj, ...]) → nil click to toggle source

Formats and writes to ios, converting parameters under control of the format string. See Kernel#sprintf for details.

 
               VALUE
rb_io_printf(int argc, const VALUE *argv, VALUE out)
{
    rb_io_write(out, rb_f_sprintf(argc, argv));
    return Qnil;
}
putc(obj) → obj click to toggle source

If obj is Numeric, write the character whose code is the least-significant byte of obj. If obj is String, write the first character of obj to ios. Otherwise, raise TypeError.

$stdout.putc "A"
$stdout.putc 65

produces:

AA

 
               static VALUE
rb_io_putc(VALUE io, VALUE ch)
{
    VALUE str;
    if (RB_TYPE_P(ch, T_STRING)) {
        str = rb_str_substr(ch, 0, 1);
    }
    else {
        char c = NUM2CHR(ch);
        str = rb_str_new(&c, 1);
    }
    rb_io_write(io, str);
    return ch;
}
puts(obj, ...) → nil click to toggle source

Writes the given object(s) to ios. Writes a newline after any that do not already end with a newline sequence. Returns nil.

The stream must be opened for writing. If called with an array argument, writes each element on a new line. Each given object that isn't a string or array will be converted by calling its to_s method. If called without arguments, outputs a single newline.

$stdout.puts("this", "is", ["a", "test"])

produces:

this
is
a
test

Note that puts always uses newlines and is not affected by the output record separator ($\).

 
               VALUE
rb_io_puts(int argc, const VALUE *argv, VALUE out)
{
    int i, n;
    VALUE line, args[2];

    /* if no argument given, print newline. */
    if (argc == 0) {
        rb_io_write(out, rb_default_rs);
        return Qnil;
    }
    for (i=0; i<argc; i++) {
        if (RB_TYPE_P(argv[i], T_STRING)) {
            line = argv[i];
            goto string;
        }
        if (rb_exec_recursive(io_puts_ary, argv[i], out)) {
            continue;
        }
        line = rb_obj_as_string(argv[i]);
      string:
        n = 0;
        args[n++] = line;
        if (RSTRING_LEN(line) == 0 ||
            !rb_str_end_with_asciichar(line, '\n')) {
            args[n++] = rb_default_rs;
        }
        rb_io_writev(out, n, args);
    }

    return Qnil;
}
pwrite(string, offset) → integer click to toggle source

Writes the given string to ios at offset using pwrite() system call. This is advantageous to combining IO#seek and IO#write in that it is atomic, allowing multiple threads/process to share the same IO object for reading the file at various locations. This bypasses any userspace buffering of the IO layer. Returns the number of bytes written. Raises SystemCallError on error and NotImplementedError if platform does not implement the system call.

File.open("out", "w") do |f|
  f.pwrite("ABCDEF", 3)   #=> 6
end

File.read("out")          #=> "\u0000\u0000\u0000ABCDEF"

 
               static VALUE
rb_io_pwrite(VALUE io, VALUE str, VALUE offset)
{
    rb_io_t *fptr;
    ssize_t n;
    struct prdwr_internal_arg arg;
    VALUE tmp;

    if (!RB_TYPE_P(str, T_STRING))
        str = rb_obj_as_string(str);

    arg.offset = NUM2OFFT(offset);

    io = GetWriteIO(io);
    GetOpenFile(io, fptr);
    rb_io_check_writable(fptr);
    arg.fd = fptr->fd;

    tmp = rb_str_tmp_frozen_acquire(str);
    arg.buf = RSTRING_PTR(tmp);
    arg.count = (size_t)RSTRING_LEN(tmp);

    n = (ssize_t)rb_thread_io_blocking_region(internal_pwrite_func, &arg, fptr->fd);
    if (n < 0) rb_sys_fail_path(fptr->pathv);
    rb_str_tmp_frozen_release(str, tmp);

    return SSIZET2NUM(n);
}
read(maxlen = nil) → string or nil click to toggle source
read(maxlen = nil, out_string) → out_string or nil

Reads bytes from the stream (in binary mode):

  • If maxlen is nil, reads all bytes.

  • Otherwise reads maxlen bytes, if available.

  • Otherwise reads all bytes.

Returns a string (either a new string or the given out_string) containing the bytes read. The encoding of the string depends on both maxLen and out_string:

  • maxlen is nil: uses internal encoding of self (regardless of whether out_string was given).

  • maxlen not nil:

    • out_string given: encoding of out_string not modified.

    • out_string not given: ASCII-8BIT is used.

Without Argument out_string

When argument out_string is omitted, the returned value is a new string:

f = File.new('t.txt')
f.read
# => "This is line one.\nThis is the second line.\nThis is the third line.\n"
f.rewind
f.read(40)      # => "This is line one.\r\nThis is the second li"
f.read(40)      # => "ne.\r\nThis is the third line.\r\n"
f.read(40)      # => nil

If maxlen is zero, returns an empty string.

With Argument out_string

When argument out_string is given, the returned value is out_string, whose content is replaced:

f = File.new('t.txt')
s = 'foo'      # => "foo"
f.read(nil, s) # => "This is line one.\nThis is the second line.\nThis is the third line.\n"
s              # => "This is line one.\nThis is the second line.\nThis is the third line.\n"
f.rewind
s = 'bar'
f.read(40, s)  # => "This is line one.\r\nThis is the second li"
s              # => "This is line one.\r\nThis is the second li"
s = 'baz'
f.read(40, s)  # => "ne.\r\nThis is the third line.\r\n"
s              # => "ne.\r\nThis is the third line.\r\n"
s = 'bat'
f.read(40, s)  # => nil
s              # => ""

Note that this method behaves like the fread() function in C. This means it retries to invoke read(2) system calls to read data with the specified maxlen (or until EOF).

This behavior is preserved even if the stream is in non-blocking mode. (This method is non-blocking-flag insensitive as other methods.)

If you need the behavior like a single read(2) system call, consider readpartial, read_nonblock, and sysread.

 
               static VALUE
io_read(int argc, VALUE *argv, VALUE io)
{
    rb_io_t *fptr;
    long n, len;
    VALUE length, str;
    int shrinkable;
#if RUBY_CRLF_ENVIRONMENT
    int previous_mode;
#endif

    rb_scan_args(argc, argv, "02", &length, &str);

    if (NIL_P(length)) {
        GetOpenFile(io, fptr);
        rb_io_check_char_readable(fptr);
        return read_all(fptr, remain_size(fptr), str);
    }
    len = NUM2LONG(length);
    if (len < 0) {
        rb_raise(rb_eArgError, "negative length %ld given", len);
    }

    shrinkable = io_setstrbuf(&str,len);

    GetOpenFile(io, fptr);
    rb_io_check_byte_readable(fptr);
    if (len == 0) {
        io_set_read_length(str, 0, shrinkable);
        return str;
    }

    READ_CHECK(fptr);
#if RUBY_CRLF_ENVIRONMENT
    previous_mode = set_binary_mode_with_seek_cur(fptr);
#endif
    n = io_fread(str, 0, len, fptr);
    io_set_read_length(str, n, shrinkable);
#if RUBY_CRLF_ENVIRONMENT
    if (previous_mode == O_TEXT) {
        setmode(fptr->fd, O_TEXT);
    }
#endif
    if (n == 0) return Qnil;

    return str;
}
read_nonblock(maxlen [, options]) → string click to toggle source
read_nonblock(maxlen, outbuf [, options]) → outbuf

Reads at most maxlen bytes from ios using the read(2) system call after O_NONBLOCK is set for the underlying file descriptor.

If the optional outbuf argument is present, it must reference a String, which will receive the data. The outbuf will contain only the received data after the method call even if it is not empty at the beginning.

read_nonblock just calls the read(2) system call. It causes all errors the read(2) system call causes: Errno::EWOULDBLOCK, Errno::EINTR, etc. The caller should care such errors.

If the exception is Errno::EWOULDBLOCK or Errno::EAGAIN, it is extended by IO::WaitReadable. So IO::WaitReadable can be used to rescue the exceptions for retrying read_nonblock.

read_nonblock causes EOFError on EOF.

On some platforms, such as Windows, non-blocking mode is not supported on IO objects other than sockets. In such cases, Errno::EBADF will be raised.

If the read byte buffer is not empty, read_nonblock reads from the buffer like readpartial. In this case, the read(2) system call is not called.

When read_nonblock raises an exception kind of IO::WaitReadable, read_nonblock should not be called until io is readable for avoiding busy loop. This can be done as follows.

# emulates blocking read (readpartial).
begin
  result = io.read_nonblock(maxlen)
rescue IO::WaitReadable
  IO.select([io])
  retry
end

Although IO#read_nonblock doesn't raise IO::WaitWritable. OpenSSL::Buffering#read_nonblock can raise IO::WaitWritable. If IO and SSL should be used polymorphically, IO::WaitWritable should be rescued too. See the document of OpenSSL::Buffering#read_nonblock for sample code.

Note that this method is identical to readpartial except the non-blocking flag is set.

By specifying a keyword argument exception to false, you can indicate that read_nonblock should not raise an IO::WaitReadable exception, but return the symbol :wait_readable instead. At EOF, it will return nil instead of raising EOFError.

 
               # File io.rb, line 62
def read_nonblock(len, buf = nil, exception: true)
  Primitive.io_read_nonblock(len, buf, exception)
end
readbyte → integer click to toggle source

Reads a byte as with IO#getbyte, but raises an EOFError on end of file.

 
               static VALUE
rb_io_readbyte(VALUE io)
{
    VALUE c = rb_io_getbyte(io);

    if (NIL_P(c)) {
        rb_eof_error();
    }
    return c;
}
readchar → string click to toggle source

Reads a one-character string from ios. Raises an EOFError on end of file.

f = File.new("testfile")
f.readchar   #=> "h"
f.readchar   #=> "e"

 
               static VALUE
rb_io_readchar(VALUE io)
{
    VALUE c = rb_io_getc(io);

    if (NIL_P(c)) {
        rb_eof_error();
    }
    return c;
}
readline(sep=$/ [, getline_args]) → string click to toggle source
readline(limit [, getline_args]) → string
readline(sep, limit [, getline_args]) → string

Reads a line as with IO#gets, but raises an EOFError on end of file.

 
               static VALUE
rb_io_readline(int argc, VALUE *argv, VALUE io)
{
    VALUE line = rb_io_gets_m(argc, argv, io);

    if (NIL_P(line)) {
        rb_eof_error();
    }
    return line;
}
readlines(sep=$/ [, getline_args]) → array click to toggle source
readlines(limit [, getline_args]) → array
readlines(sep, limit [, getline_args]) → array

Reads all of the lines in ios, and returns them in an array. Lines are separated by the optional sep. If sep is nil, the rest of the stream is returned as a single record. If the first argument is an integer, or an optional second argument is given, the returning string would not be longer than the given value in bytes. The stream must be opened for reading or an IOError will be raised.

f = File.new("testfile")
f.readlines[0]   #=> "This is line one\n"

f = File.new("testfile", chomp: true)
f.readlines[0]   #=> "This is line one"

See IO.readlines for details about getline_args.

 
               static VALUE
rb_io_readlines(int argc, VALUE *argv, VALUE io)
{
    struct getline_arg args;

    prepare_getline_args(argc, argv, &args, io);
    return io_readlines(&args, io);
}
readpartial(maxlen) → string click to toggle source
readpartial(maxlen, out_string) → out_string

Reads up to maxlen bytes from the stream; returns a string (either a new string or the given out_string). Its encoding is:

  • The unchanged encoding of out_string, if out_string is given.

  • ASCII-8BIT, otherwise.

  • Contains maxlen bytes from the stream, if available.

  • Otherwise contains all available bytes, if any available.

  • Otherwise is an empty string.

With the single non-negative integer argument maxlen given, returns a new string:

f = File.new('t.txt')
f.readpartial(30) # => "This is line one.\nThis is the"
f.readpartial(30) # => " second line.\nThis is the thi"
f.readpartial(30) # => "rd line.\n"
f.eof             # => true
f.readpartial(30) # Raises EOFError.

With both argument maxlen and string argument out_string given, returns modified out_string:

f = File.new('t.txt')
s = 'foo'
f.readpartial(30, s) # => "This is line one.\nThis is the"
s = 'bar'
f.readpartial(0, s)  # => ""

This method is useful for a stream such as a pipe, a socket, or a tty. It blocks only when no data is immediately available. This means that it blocks only when all of the following are true:

  • The byte buffer in the stream is empty.

  • The content of the stream is empty.

  • The stream is not at EOF.

When blocked, the method waits for either more data or EOF on the stream:

  • If more data is read, the method returns the data.

  • If EOF is reached, the method raises EOFError.

When not blocked, the method responds immediately:

  • Returns data from the buffer if there is any.

  • Otherwise returns data from the stream if there is any.

  • Otherwise raises EOFError if the stream has reached EOF.

Note that this method is similar to sysread. The differences are:

  • If the byte buffer is not empty, read from the byte buffer instead of “sysread for buffered IO (IOError)”.

  • It doesn't cause Errno::EWOULDBLOCK and Errno::EINTR. When readpartial meets EWOULDBLOCK and EINTR by read system call, readpartial retries the system call.

The latter means that readpartial is non-blocking-flag insensitive. It blocks on the situation IO#sysread causes Errno::EWOULDBLOCK as if the fd is blocking mode.

Examples:

#                        # Returned      Buffer Content    Pipe Content
r, w = IO.pipe           #
w << 'abc'               #               ""                "abc".
r.readpartial(4096)      # => "abc"      ""                ""
r.readpartial(4096)      # (Blocks because buffer and pipe are empty.)

#                        # Returned      Buffer Content    Pipe Content
r, w = IO.pipe           #
w << 'abc'               #               ""                "abc"
w.close                  #               ""                "abc" EOF
r.readpartial(4096)      # => "abc"      ""                 EOF
r.readpartial(4096)      # raises EOFError

#                        # Returned      Buffer Content    Pipe Content
r, w = IO.pipe           #
w << "abc\ndef\n"        #               ""                "abc\ndef\n"
r.gets                   # => "abc\n"    "def\n"           ""
w << "ghi\n"             #               "def\n"           "ghi\n"
r.readpartial(4096)      # => "def\n"    ""                "ghi\n"
r.readpartial(4096)      # => "ghi\n"    ""                ""

 
               static VALUE
io_readpartial(int argc, VALUE *argv, VALUE io)
{
    VALUE ret;

    ret = io_getpartial(argc, argv, io, Qnil, 0);
    if (NIL_P(ret))
        rb_eof_error();
    return ret;
}
reopen(other_IO) → ios click to toggle source
reopen(path, mode [, opt]) → ios

Reassociates ios with the I/O stream given in other_IO or to a new stream opened on path. This may dynamically change the actual class of this stream. The mode and opt parameters accept the same values as IO.open.

f1 = File.new("testfile")
f2 = File.new("testfile")
f2.readlines[0]   #=> "This is line one\n"
f2.reopen(f1)     #=> #<File:testfile>
f2.readlines[0]   #=> "This is line one\n"

 
               static VALUE
rb_io_reopen(int argc, VALUE *argv, VALUE file)
{
    VALUE fname, nmode, opt;
    int oflags;
    rb_io_t *fptr;

    if (rb_scan_args(argc, argv, "11:", &fname, &nmode, &opt) == 1) {
        VALUE tmp = rb_io_check_io(fname);
        if (!NIL_P(tmp)) {
            return io_reopen(file, tmp);
        }
    }

    FilePathValue(fname);
    rb_io_taint_check(file);
    fptr = RFILE(file)->fptr;
    if (!fptr) {
        fptr = RFILE(file)->fptr = ZALLOC(rb_io_t);
    }

    if (!NIL_P(nmode) || !NIL_P(opt)) {
        int fmode;
        convconfig_t convconfig;

        rb_io_extract_modeenc(&nmode, 0, opt, &oflags, &fmode, &convconfig);
        if (IS_PREP_STDIO(fptr) &&
            ((fptr->mode & FMODE_READWRITE) & (fmode & FMODE_READWRITE)) !=
            (fptr->mode & FMODE_READWRITE)) {
            rb_raise(rb_eArgError,
                     "%s can't change access mode from \"%s\" to \"%s\"",
                     PREP_STDIO_NAME(fptr), rb_io_fmode_modestr(fptr->mode),
                     rb_io_fmode_modestr(fmode));
        }
        fptr->mode = fmode;
        fptr->encs = convconfig;
    }
    else {
        oflags = rb_io_fmode_oflags(fptr->mode);
    }

    fptr->pathv = fname;
    if (fptr->fd < 0) {
        fptr->fd = rb_sysopen(fptr->pathv, oflags, 0666);
        fptr->stdio_file = 0;
        return file;
    }

    if (fptr->mode & FMODE_WRITABLE) {
        if (io_fflush(fptr) < 0)
            rb_sys_fail_on_write(fptr);
    }
    fptr->rbuf.off = fptr->rbuf.len = 0;

    if (fptr->stdio_file) {
        int e = rb_freopen(rb_str_encode_ospath(fptr->pathv),
                           rb_io_oflags_modestr(oflags),
                           fptr->stdio_file);
        if (e) rb_syserr_fail_path(e, fptr->pathv);
        fptr->fd = fileno(fptr->stdio_file);
        rb_fd_fix_cloexec(fptr->fd);
#ifdef USE_SETVBUF
        if (setvbuf(fptr->stdio_file, NULL, _IOFBF, 0) != 0)
            rb_warn("setvbuf() can't be honoured for %"PRIsVALUE, fptr->pathv);
#endif
        if (fptr->stdio_file == stderr) {
            if (setvbuf(fptr->stdio_file, NULL, _IONBF, BUFSIZ) != 0)
                rb_warn("setvbuf() can't be honoured for %"PRIsVALUE, fptr->pathv);
        }
        else if (fptr->stdio_file == stdout && isatty(fptr->fd)) {
            if (setvbuf(fptr->stdio_file, NULL, _IOLBF, BUFSIZ) != 0)
                rb_warn("setvbuf() can't be honoured for %"PRIsVALUE, fptr->pathv);
        }
    }
    else {
        int tmpfd = rb_sysopen(fptr->pathv, oflags, 0666);
        int err = 0;
        if (rb_cloexec_dup2(tmpfd, fptr->fd) < 0)
            err = errno;
        (void)close(tmpfd);
        if (err) {
            rb_syserr_fail_path(err, fptr->pathv);
        }
    }

    return file;
}
rewind → 0 click to toggle source

Repositions the stream to its beginning, setting both the position and the line number to zero; see Position and Line Number:

f = File.open('t.txt')
f.tell     # => 0
f.lineno   # => 0
f.readline # => "This is line one.\n"
f.tell     # => 19
f.lineno   # => 1
f.rewind   # => 0
f.tell     # => 0
f.lineno   # => 0

Note that this method cannot be used with streams such as pipes, ttys, and sockets.

 
               static VALUE
rb_io_rewind(VALUE io)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    if (io_seek(fptr, 0L, 0) < 0 && errno) rb_sys_fail_path(fptr->pathv);
    if (io == ARGF.current_file) {
        ARGF.lineno -= fptr->lineno;
    }
    fptr->lineno = 0;
    if (fptr->readconv) {
        clear_readconv(fptr);
    }

    return INT2FIX(0);
}
seek(offset, whence = IO::SEEK_SET) → 0 click to toggle source

Seeks to the position given by integer offset (see Position) and constant whence, which is one of:

  • :CUR or IO::SEEK_CUR: Repositions the stream to its current position plus the given offset:

    f = File.open('t.txt')
f.tell            # => 0
f.seek(20, :CUR)  # => 0
f.tell            # => 20
f.seek(-10, :CUR) # => 0
f.tell            # => 10

  • :END or IO::SEEK_END: Repositions the stream to its end plus the given offset:

    f = File.open('t.txt')
f.tell            # => 0
f.seek(0, :END)   # => 0  # Repositions to stream end.
f.tell            # => 70
f.seek(-20, :END) # => 0
f.tell            # => 50
f.seek(-40, :END) # => 0
f.tell            # => 30

  • :SET or IO:SEEK_SET: Repositions the stream to the given offset:

    f = File.open('t.txt')
f.tell            # => 0
f.seek(20, :SET) # => 0
f.tell           # => 20
f.seek(40, :SET) # => 0
f.tell           # => 40

Related: IO#pos=, IO#tell.

 
               static VALUE
rb_io_seek_m(int argc, VALUE *argv, VALUE io)
{
    VALUE offset, ptrname;
    int whence = SEEK_SET;

    if (rb_scan_args(argc, argv, "11", &offset, &ptrname) == 2) {
        whence = interpret_seek_whence(ptrname);
    }

    return rb_io_seek(io, offset, whence);
}
set_encoding(ext_enc) → io click to toggle source
set_encoding("ext_enc:int_enc") → io
set_encoding(ext_enc, int_enc) → io
set_encoding("ext_enc:int_enc", opt) → io
set_encoding(ext_enc, int_enc, opt) → io

If single argument is specified, read string from io is tagged with the encoding specified. If encoding is a colon separated two encoding names “A:B”, the read string is converted from encoding A (external encoding) to encoding B (internal encoding), then tagged with B. If two arguments are specified, those must be encoding objects or encoding names, and the first one is the external encoding, and the second one is the internal encoding. If the external encoding and the internal encoding is specified, optional hash argument specify the conversion option.

 
               static VALUE
rb_io_set_encoding(int argc, VALUE *argv, VALUE io)
{
    rb_io_t *fptr;
    VALUE v1, v2, opt;

    if (!RB_TYPE_P(io, T_FILE)) {
        return forward(io, id_set_encoding, argc, argv);
    }

    argc = rb_scan_args(argc, argv, "11:", &v1, &v2, &opt);
    GetOpenFile(io, fptr);
    io_encoding_set(fptr, v1, v2, opt);
    return io;
}
set_encoding_by_bom → encoding or nil click to toggle source

Checks if ios starts with a BOM, and then consumes it and sets the external encoding. Returns the result encoding if found, or nil. If ios is not binmode or its encoding has been set already, an exception will be raised.

File.write("bom.txt", "\u{FEFF}abc")
ios = File.open("bom.txt", "rb")
ios.set_encoding_by_bom    #=>  #<Encoding:UTF-8>

File.write("nobom.txt", "abc")
ios = File.open("nobom.txt", "rb")
ios.set_encoding_by_bom    #=>  nil

 
               static VALUE
rb_io_set_encoding_by_bom(VALUE io)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    if (!(fptr->mode & FMODE_BINMODE)) {
        rb_raise(rb_eArgError, "ASCII incompatible encoding needs binmode");
    }
    if (fptr->encs.enc2) {
        rb_raise(rb_eArgError, "encoding conversion is set");
    }
    else if (fptr->encs.enc && fptr->encs.enc != rb_ascii8bit_encoding()) {
        rb_raise(rb_eArgError, "encoding is set to %s already",
                 rb_enc_name(fptr->encs.enc));
    }
    if (!io_set_encoding_by_bom(io)) return Qnil;
    return rb_enc_from_encoding(fptr->encs.enc);
}
stat → stat click to toggle source

Returns status information for ios as an object of type File::Stat.

f = File.new("testfile")
s = f.stat
"%o" % s.mode   #=> "100644"
s.blksize       #=> 4096
s.atime         #=> Wed Apr 09 08:53:54 CDT 2003

 
               static VALUE
rb_io_stat(VALUE obj)
{
    rb_io_t *fptr;
    struct stat st;

    GetOpenFile(obj, fptr);
    if (fstat(fptr->fd, &st) == -1) {
        rb_sys_fail_path(fptr->pathv);
    }
    return rb_stat_new(&st);
}
sync → true or false click to toggle source

Returns the current sync mode of the stream. When sync mode is true, all output is immediately flushed to the underlying operating system and is not buffered by Ruby internally. See also fsync.

f = File.open('t.tmp', 'w')
f.sync # => false
f.sync = true
f.sync # => true

 
               static VALUE
rb_io_sync(VALUE io)
{
    rb_io_t *fptr;

    io = GetWriteIO(io);
    GetOpenFile(io, fptr);
    return RBOOL(fptr->mode & FMODE_SYNC);
}
sync = boolean → boolean click to toggle source

Sets the sync mode for the stream to the given value; returns the given value.

Values for the sync mode:

  • true: All output is immediately flushed to the underlying operating system and is not buffered internally.

  • false: Output may be buffered internally.

Example;

f = File.open('t.tmp', 'w')
f.sync # => false
f.sync = true
f.sync # => true

Related: IO#fsync.

 
               static VALUE
rb_io_set_sync(VALUE io, VALUE sync)
{
    rb_io_t *fptr;

    io = GetWriteIO(io);
    GetOpenFile(io, fptr);
    if (RTEST(sync)) {
        fptr->mode |= FMODE_SYNC;
    }
    else {
        fptr->mode &= ~FMODE_SYNC;
    }
    return sync;
}
sysread(maxlen[, outbuf]) → string click to toggle source

Reads maxlen bytes from ios using a low-level read and returns them as a string. Do not mix with other methods that read from ios or you may get unpredictable results.

If the optional outbuf argument is present, it must reference a String, which will receive the data. The outbuf will contain only the received data after the method call even if it is not empty at the beginning.

Raises SystemCallError on error and EOFError at end of file.

f = File.new("testfile")
f.sysread(16)   #=> "This is line one"

 
               static VALUE
rb_io_sysread(int argc, VALUE *argv, VALUE io)
{
    VALUE len, str;
    rb_io_t *fptr;
    long n, ilen;
    struct io_internal_read_struct iis;
    int shrinkable;

    rb_scan_args(argc, argv, "11", &len, &str);
    ilen = NUM2LONG(len);

    shrinkable = io_setstrbuf(&str, ilen);
    if (ilen == 0) return str;

    GetOpenFile(io, fptr);
    rb_io_check_byte_readable(fptr);

    if (READ_DATA_BUFFERED(fptr)) {
        rb_raise(rb_eIOError, "sysread for buffered IO");
    }

    rb_io_check_closed(fptr);

    io_setstrbuf(&str, ilen);
    iis.th = rb_thread_current();
    iis.fptr = fptr;
    iis.nonblock = 0;
    iis.buf = RSTRING_PTR(str);
    iis.capa = ilen;
    n = read_internal_locktmp(str, &iis);

    if (n < 0) {
        rb_sys_fail_path(fptr->pathv);
    }

    io_set_read_length(str, n, shrinkable);

    if (n == 0 && ilen > 0) {
        rb_eof_error();
    }

    return str;
}
sysseek(offset, whence=IO::SEEK_SET) → integer click to toggle source

Seeks to a given offset in the stream according to the value of whence (see IO#seek for values of whence). Returns the new offset into the file.

f = File.new("testfile")
f.sysseek(-13, IO::SEEK_END)   #=> 53
f.sysread(10)                  #=> "And so on."

 
               static VALUE
rb_io_sysseek(int argc, VALUE *argv, VALUE io)
{
    VALUE offset, ptrname;
    int whence = SEEK_SET;
    rb_io_t *fptr;
    off_t pos;

    if (rb_scan_args(argc, argv, "11", &offset, &ptrname) == 2) {
        whence = interpret_seek_whence(ptrname);
    }
    pos = NUM2OFFT(offset);
    GetOpenFile(io, fptr);
    if ((fptr->mode & FMODE_READABLE) &&
        (READ_DATA_BUFFERED(fptr) || READ_CHAR_PENDING(fptr))) {
        rb_raise(rb_eIOError, "sysseek for buffered IO");
    }
    if ((fptr->mode & FMODE_WRITABLE) && fptr->wbuf.len) {
        rb_warn("sysseek for buffered IO");
    }
    errno = 0;
    pos = lseek(fptr->fd, pos, whence);
    if (pos < 0 && errno) rb_sys_fail_path(fptr->pathv);

    return OFFT2NUM(pos);
}
syswrite(string) → integer click to toggle source

Writes the given string to ios using a low-level write. Returns the number of bytes written. Do not mix with other methods that write to ios or you may get unpredictable results. Raises SystemCallError on error.

f = File.new("out", "w")
f.syswrite("ABCDEF")   #=> 6

 
               static VALUE
rb_io_syswrite(VALUE io, VALUE str)
{
    VALUE tmp;
    rb_io_t *fptr;
    long n, len;
    const char *ptr;

    if (!RB_TYPE_P(str, T_STRING))
        str = rb_obj_as_string(str);

    io = GetWriteIO(io);
    GetOpenFile(io, fptr);
    rb_io_check_writable(fptr);

    if (fptr->wbuf.len) {
        rb_warn("syswrite for buffered IO");
    }

    tmp = rb_str_tmp_frozen_acquire(str);
    RSTRING_GETMEM(tmp, ptr, len);
    n = rb_write_internal(fptr, ptr, len);
    if (n < 0) rb_sys_fail_path(fptr->pathv);
    rb_str_tmp_frozen_release(str, tmp);

    return LONG2FIX(n);
}
tell → integer click to toggle source

Returns the current position (in bytes) in self (see Position):

f = File.new('t.txt')
f.tell     # => 0
f.readline # => "This is line one.\n"
f.tell     # => 19

Related: IO#pos=, IO#seek.

IO#pos is an alias for IO#tell.

 
               static VALUE
rb_io_tell(VALUE io)
{
    rb_io_t *fptr;
    off_t pos;

    GetOpenFile(io, fptr);
    pos = io_tell(fptr);
    if (pos < 0 && errno) rb_sys_fail_path(fptr->pathv);
    pos -= fptr->rbuf.len;
    return OFFT2NUM(pos);
}
to_i() click to toggle source
Alias for: fileno
to_io → self click to toggle source

Returns self.

 
               static VALUE
rb_io_to_io(VALUE io)
{
    return io;
}
tty? → true or false click to toggle source

Returns true if ios is associated with a terminal device (tty), false otherwise.

File.new("testfile").isatty   #=> false
File.new("/dev/tty").isatty   #=> true

 
               static VALUE
rb_io_isatty(VALUE io)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    return RBOOL(isatty(fptr->fd) != 0);
}
ungetbyte(string) → nil click to toggle source
ungetbyte(integer) → nil

Pushes back bytes (passed as a parameter) onto ios, such that a subsequent buffered read will return it. It is only guaranteed to support a single byte, and only if ungetbyte or ungetc has not already been called on ios since the previous read of at least a single byte from ios. However, it can support additional bytes if there is space in the internal buffer to allow for it.

f = File.new("testfile")   #=> #<File:testfile>
b = f.getbyte              #=> 0x38
f.ungetbyte(b)             #=> nil
f.getbyte                  #=> 0x38

If given an integer, only uses the lower 8 bits of the integer as the byte to push.

f = File.new("testfile")   #=> #<File:testfile>
f.ungetbyte(0x102)         #=> nil
f.getbyte                  #=> 0x2

Calling this method prepends to the existing buffer, even if the method has already been called previously:

f = File.new("testfile")   #=> #<File:testfile>
f.ungetbyte("ab")          #=> nil
f.ungetbyte("cd")          #=> nil
f.read(5)                  #=> "cdab8"

Has no effect with unbuffered reads (such as IO#sysread).

 
               VALUE
rb_io_ungetbyte(VALUE io, VALUE b)
{
    rb_io_t *fptr;

    GetOpenFile(io, fptr);
    rb_io_check_byte_readable(fptr);
    switch (TYPE(b)) {
      case T_NIL:
        return Qnil;
      case T_FIXNUM:
      case T_BIGNUM: ;
        VALUE v = rb_int_modulo(b, INT2FIX(256));
        unsigned char c = NUM2INT(v) & 0xFF;
        b = rb_str_new((const char *)&c, 1);
        break;
      default:
        SafeStringValue(b);
    }
    io_ungetbyte(b, fptr);
    return Qnil;
}
ungetc(integer) → nil click to toggle source
ungetc(string) → nil

Pushes back characters (passed as a parameter) onto ios, such that a subsequent buffered read will return it. It is only guaranteed to support a single byte, and only if ungetbyte or ungetc has not already been called on ios since the previous read of at least a single byte from ios. However, it can support additional bytes if there is space in the internal buffer to allow for it.

f = File.new("testfile")   #=> #<File:testfile>
c = f.getc                 #=> "8"
f.ungetc(c)                #=> nil
f.getc                     #=> "8"

If given an integer, the integer must represent a valid codepoint in the external encoding of ios.

Calling this method prepends to the existing buffer, even if the method has already been called previously:

f = File.new("testfile")   #=> #<File:testfile>
f.ungetc("ab")             #=> nil
f.ungetc("cd")             #=> nil
f.read(5)                  #=> "cdab8"

Has no effect with unbuffered reads (such as IO#sysread).

 
               VALUE
rb_io_ungetc(VALUE io, VALUE c)
{
    rb_io_t *fptr;
    long len;

    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);
    if (FIXNUM_P(c)) {
        c = rb_enc_uint_chr(FIX2UINT(c), io_read_encoding(fptr));
    }
    else if (RB_BIGNUM_TYPE_P(c)) {
        c = rb_enc_uint_chr(NUM2UINT(c), io_read_encoding(fptr));
    }
    else {
        SafeStringValue(c);
    }
    if (NEED_READCONV(fptr)) {
        SET_BINARY_MODE(fptr);
        len = RSTRING_LEN(c);
#if SIZEOF_LONG > SIZEOF_INT
        if (len > INT_MAX)
            rb_raise(rb_eIOError, "ungetc failed");
#endif
        make_readconv(fptr, (int)len);
        if (fptr->cbuf.capa - fptr->cbuf.len < len)
            rb_raise(rb_eIOError, "ungetc failed");
        if (fptr->cbuf.off < len) {
            MEMMOVE(fptr->cbuf.ptr+fptr->cbuf.capa-fptr->cbuf.len,
                    fptr->cbuf.ptr+fptr->cbuf.off,
                    char, fptr->cbuf.len);
            fptr->cbuf.off = fptr->cbuf.capa-fptr->cbuf.len;
        }
        fptr->cbuf.off -= (int)len;
        fptr->cbuf.len += (int)len;
        MEMMOVE(fptr->cbuf.ptr+fptr->cbuf.off, RSTRING_PTR(c), char, len);
    }
    else {
        NEED_NEWLINE_DECORATOR_ON_READ_CHECK(fptr);
        io_ungetbyte(c, fptr);
    }
    return Qnil;
}
write(*objects) → integer click to toggle source

Writes each of the given objects to self, which must be opened for writing (see Modes); returns the total number bytes written; each of objects that is not a string is converted via method to_s:

$stdout.write('Hello', ', ', 'World!', "\n") # => 14
$stdout.write('foo', :bar, 2, "\n")          # => 8

Output:

Hello, World!
foobar2
 
               static VALUE
io_write_m(int argc, VALUE *argv, VALUE io)
{
    if (argc != 1) {
        return io_writev(argc, argv, io);
    }
    else {
        VALUE str = argv[0];
        return io_write(io, str, 0);
    }
}
write_nonblock(string) → integer click to toggle source
write_nonblock(string [, options]) → integer

Writes the given string to ios using the write(2) system call after O_NONBLOCK is set for the underlying file descriptor.

It returns the number of bytes written.

write_nonblock just calls the write(2) system call. It causes all errors the write(2) system call causes: Errno::EWOULDBLOCK, Errno::EINTR, etc. The result may also be smaller than string.length (partial write). The caller should care such errors and partial write.

If the exception is Errno::EWOULDBLOCK or Errno::EAGAIN, it is extended by IO::WaitWritable. So IO::WaitWritable can be used to rescue the exceptions for retrying write_nonblock.

# Creates a pipe.
r, w = IO.pipe

# write_nonblock writes only 65536 bytes and return 65536.
# (The pipe size is 65536 bytes on this environment.)
s = "a" * 100000
p w.write_nonblock(s)     #=> 65536

# write_nonblock cannot write a byte and raise EWOULDBLOCK (EAGAIN).
p w.write_nonblock("b")   # Resource temporarily unavailable (Errno::EAGAIN)

If the write buffer is not empty, it is flushed at first.

When write_nonblock raises an exception kind of IO::WaitWritable, write_nonblock should not be called until io is writable for avoiding busy loop. This can be done as follows.

begin
  result = io.write_nonblock(string)
rescue IO::WaitWritable, Errno::EINTR
  IO.select(nil, [io])
  retry
end

Note that this doesn't guarantee to write all data in string. The length written is reported as result and it should be checked later.

On some platforms such as Windows, write_nonblock is not supported according to the kind of the IO object. In such cases, write_nonblock raises Errno::EBADF.

By specifying a keyword argument exception to false, you can indicate that write_nonblock should not raise an IO::WaitWritable exception, but return the symbol :wait_writable instead.

 
               # File io.rb, line 120
def write_nonblock(buf, exception: true)
  Primitive.io_write_nonblock(buf, exception)
end
There is an updated format of the API docs for this version here.