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Class: IO

Relationships & Source Files
Namespace Children
Modules:
Classes:
Extension / Inclusion / Inheritance Descendants
Subclasses:
Super Chains via Extension / Inclusion / Inheritance
Instance Chain:
Inherits: Object
Defined in: io.c,
file.c,
prelude.rb

Overview

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 .new for these options. See Kernel.open for details of the various command formats described above.

.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"

Constant Summary

::File::Constants - Included

APPEND, BINARY, CREAT, DIRECT, DSYNC, EXCL, LOCK_EX, LOCK_NB, LOCK_SH, LOCK_UN, NOATIME, NOCTTY, NOFOLLOW, NONBLOCK, NULL, RDONLY, RDWR, RSYNC, SHARE_DELETE, SYNC, TMPFILE, TRUNC, WRONLY

Class Method Summary

Instance Attribute Summary

Instance Method Summary

::Enumerable - Included

#all?

Passes each element of the collection to the given block.

#any?

Passes each element of the collection to the given block.

#chain

Returns an enumerator object generated from this enumerator and given enumerables.

#chunk

Enumerates over the items, chunking them together based on the return value of the block.

#chunk_while

Creates an enumerator for each chunked elements.

#collect

Alias for Enumerable#map.

#collect_concat
#count

Returns the number of items in enum through enumeration.

#cycle

Calls block for each element of enum repeatedly n times or forever if none or nil is given.

#detect

Alias for Enumerable#find.

#drop

Drops first n elements from enum, and returns rest elements in an array.

#drop_while

Drops elements up to, but not including, the first element for which the block returns nil or false and returns an array containing the remaining elements.

#each_cons

Iterates the given block for each array of consecutive <n> elements.

#each_entry

Calls block once for each element in self, passing that element as a parameter, converting multiple values from yield to an array.

#each_slice

Iterates the given block for each slice of <n> elements.

#each_with_index

Calls block with two arguments, the item and its index, for each item in enum.

#each_with_object

Iterates the given block for each element with an arbitrary object given, and returns the initially given object.

#entries

Alias for Enumerable#to_a.

#filter

Returns an array containing all elements of enum for which the given block returns a true value.

#filter_map

Returns a new array containing the truthy results (everything except false or nil) of running the block for every element in enum.

#find

Passes each entry in enum to block.

#find_all
#find_index

Compares each entry in enum with value or passes to block.

#first

Returns the first element, or the first n elements, of the enumerable.

#flat_map

Returns a new array with the concatenated results of running block once for every element in enum.

#grep

Returns an array of every element in enum for which Pattern === element.

#grep_v

Inverted version of Enumerable#grep.

#group_by

Groups the collection by result of the block.

#include?
#inject

Combines all elements of enum by applying a binary operation, specified by a block or a symbol that names a method or operator.

#lazy

Returns an ::Enumerator::Lazy, which redefines most ::Enumerable methods to postpone enumeration and enumerate values only on an as-needed basis.

#map

Returns a new array with the results of running block once for every element in enum.

#max

Returns the object in enum with the maximum value.

#max_by

Returns the object in enum that gives the maximum value from the given block.

#member?

Returns true if any member of enum equals obj.

#min

Returns the object in enum with the minimum value.

#min_by

Returns the object in enum that gives the minimum value from the given block.

#minmax

Returns a two element array which contains the minimum and the maximum value in the enumerable.

#minmax_by

Returns a two element array containing the objects in enum that correspond to the minimum and maximum values respectively from the given block.

#none?

Passes each element of the collection to the given block.

#one?

Passes each element of the collection to the given block.

#partition

Returns two arrays, the first containing the elements of enum for which the block evaluates to true, the second containing the rest.

#reduce
#reject

Returns an array for all elements of enum for which the given block returns false.

#reverse_each

Builds a temporary array and traverses that array in reverse order.

#select
#slice_after

Creates an enumerator for each chunked elements.

#slice_before

Creates an enumerator for each chunked elements.

#slice_when

Creates an enumerator for each chunked elements.

#sort

Returns an array containing the items in enum sorted.

#sort_by

Sorts enum using a set of keys generated by mapping the values in enum through the given block.

#sum

Returns the sum of elements in an ::Enumerable.

#take

Returns first n elements from enum.

#take_while

Passes elements to the block until the block returns nil or false, then stops iterating and returns an array of all prior elements.

#tally

Tallys the collection.

#to_a

Returns an array containing the items in enum.

#to_h

Returns the result of interpreting enum as a list of [key, value] pairs.

#uniq

Returns a new array by removing duplicate values in self.

#zip

Takes one element from enum and merges corresponding elements from each args.

Constructor Details

.new(*args)

This method is for internal use only.
[ GitHub ]

  
# File 'io.c', line 8387

static VALUE
rb_io_s_new(int argc, VALUE *argv, VALUE klass)
{
    if (rb_block_given_p()) {
	VALUE cname = rb_obj_as_string(klass);

	rb_warn("%"PRIsVALUE"::new() does not take block; use %"PRIsVALUE"::open() instead",
		cname, cname);
    }
    return rb_class_new_instance(argc, argv, klass);
}

#new(fd[, mode][, opt]) ⇒ IO

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 .sysopen and .for_fd.

.new is called by various ::File and IO opening methods such as .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.

[ GitHub ]

  
# File 'io.c', line 8249

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->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;
}

Class Method Details

.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".

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

  
# File 'io.c', line 10589

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 .binwrite(name, string, [offset], open_args) ⇒ Integer

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

[ GitHub ]

  
# File 'io.c', line 10737

static VALUE
rb_io_s_binwrite(int argc, VALUE *argv, VALUE io)
{
    return io_s_write(argc, argv, io, 1);
}

.copy_stream(src, dst) .copy_stream(src, dst, copy_length) .copy_stream(src, dst, copy_length, src_offset)

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, copy_stream doesn't move the current file offset.

[ GitHub ]

  
# File 'io.c', line 11653

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;

    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

Synonym for .new.

[ GitHub ]

  
# File 'io.c', line 8408

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| ... } ⇒ nil .foreach(name, limit[, getline_args, open_args]) {|line| ... } ⇒ nil .foreach(name, sep, limit[, getline_args, open_args]) {|line| ... } ⇒ nil .foreach(...) ⇒ 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.

IO.foreach("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 .readlines for details about getline_args. And see also .read for details about open_args.

[ GitHub ]

  
# File 'io.c', line 10418

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);
}

.open(filename, mode = "r"[, opt]) ⇒ File .open(filename[, mode [, perm]][, opt]) ⇒ File .open(filename, mode = "r"[, opt]) {|file| ... } ⇒ Object .open(filename[, mode [, perm]][, opt]) {|file| ... } ⇒ Object

Alias for File.open. With no associated block, open is a synonym for .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, open returns the value of the block.

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

[ GitHub ]

.pipeIO .pipe(ext_enc) ⇒ IO .pipe("ext_enc:int_enc"[, opt]) ⇒ IO .pipe(ext_enc, int_enc[, opt]) ⇒ IO

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>
[ GitHub ]

  
# File 'io.c', line 10266

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 DEFAULT_TEXTMODE
    if ((fptr->mode & FMODE_TEXTMODE) && (fmode & FMODE_BINMODE)) {
	fptr->mode &= ~FMODE_TEXTMODE;
	setmode(fptr->fd, O_BINARY);
    }
#if defined(RUBY_TEST_CRLF_ENVIRONMENT) || defined(_WIN32)
    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,], mode = "r"[, opt]) ⇒ IO .popen([env,], mode = "r"[, opt]) {|io| ... } ⇒ Object

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 #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 .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 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;
[ GitHub ]

  
# File 'io.c', line 6885

static VALUE
rb_io_s_popen(int argc, VALUE *argv, VALUE klass)
{
    const char *modestr;
    VALUE pname, pmode = Qnil, port, tmp, opt = Qnil, env = Qnil, execarg_obj = Qnil;
    int oflags, fmode;
    convconfig_t convconfig;

    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);
	}
    }

    tmp = rb_check_array_type(pname);
    if (!NIL_P(tmp)) {
	long len = RARRAY_LEN(tmp);
#if SIZEOF_LONG > SIZEOF_INT
	if (len > INT_MAX) {
	    rb_raise(rb_eArgError, "too many arguments");
	}
#endif
        execarg_obj = rb_execarg_new((int)len, RARRAY_CONST_PTR(tmp), FALSE, FALSE);
	RB_GC_GUARD(tmp);
    }
    else {
	SafeStringValue(pname);
	execarg_obj = Qnil;
	if (!is_popen_fork(pname))
            execarg_obj = rb_execarg_new(1, &pname, TRUE, FALSE);
    }
    if (!NIL_P(execarg_obj)) {
	if (!NIL_P(opt))
	    opt = rb_execarg_extract_options(execarg_obj, opt);
	if (!NIL_P(env))
	    rb_execarg_setenv(execarg_obj, env);
    }
    rb_io_extract_modeenc(&pmode, 0, opt, &oflags, &fmode, &convconfig);
    modestr = rb_io_oflags_modestr(oflags);

    port = pipe_open(execarg_obj, modestr, fmode, &convconfig);
    if (NIL_P(port)) {
	/* child */
	if (rb_block_given_p()) {
	    rb_yield(Qnil);
            rb_io_flush(rb_stdout);
            rb_io_flush(rb_stderr);
	    _exit(0);
	}
	return Qnil;
    }
    RBASIC_SET_CLASS(port, klass);
    if (rb_block_given_p()) {
	return rb_ensure(rb_yield, port, pipe_close, port);
    }
    return port;
}

.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 ("|"), a subprocess is created in the same way as Kernel.open, and its output is returned.

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:

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

  
# File 'io.c', line 10550

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 .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.

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

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

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 .read for details about open_args.

[ GitHub ]

  
# File 'io.c', line 10472

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?

Alias for Kernel.select. 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.

select peeks the buffer of IO objects for testing readability. If the IO buffer is not empty, 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 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 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 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 select is preferred for IO like objects such as OpenSSL::SSL::SSLSocket. It has #to_io method to return underlying IO object. select calls #to_io to obtain the file descriptor to wait.

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

The most likely situation is that OpenSSL::SSL::SSLSocket buffers some data. select doesn't see the buffer. So 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, 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 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 select before #readpartial works well as usual. However it is not the best way to use select.

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

Blocking write (#write) can be emulated using #write_nonblock and 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

.sysopen(path, [mode, [perm]]) ⇒ Integer

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

IO.sysopen("testfile")   #=> 3
[ GitHub ]

  
# File 'io.c', line 7047

static VALUE
rb_io_s_sysopen(int argc, VALUE *argv)
{
    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(obj) ⇒ IO?

Try to convert obj into an IO, using to_io method. Returns converted IO or nil if obj cannot be converted for any reason.

IO.try_convert(STDOUT)     #=> STDOUT
IO.try_convert("STDOUT")   #=> nil

require 'zlib'
f = open("/tmp/zz.gz")       #=> #<File:/tmp/zz.gz>
z = Zlib::GzipReader.open(f) #=> #<Zlib::GzipReader:0x81d8744>
IO.try_convert(z)            #=> #<File:/tmp/zz.gz>
[ GitHub ]

  
# File 'io.c', line 768

static VALUE
rb_io_s_try_convert(VALUE dummy, VALUE io)
{
    return rb_io_check_io(io);
}

.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.

IO.write("testfile", "0123456789", 20)  #=> 10
# File could contain:  "This is line one\nThi0123456789two\nThis is line three\nAnd so on...\n"
IO.write("testfile", "0123456789")      #=> 10
# File would now read: "0123456789"

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.

[ GitHub ]

  
# File 'io.c', line 10722

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

Instance Attribute Details

#autoclose=(bool) ⇒ Boolean (rw)

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
[ GitHub ]

  
# File 'io.c', line 8449

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?Boolean (rw)

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

[ GitHub ]

  
# File 'io.c', line 8424

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;
}

#binmodeIO (readonly)

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

[ GitHub ]

  
# File 'io.c', line 5399

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?Boolean (readonly)

Returns true if ios is binmode.

[ GitHub ]

  
# File 'io.c', line 5418

static VALUE
rb_io_binmode_p(VALUE io)
{
    rb_io_t *fptr;
    GetOpenFile(io, fptr);
    return fptr->mode & FMODE_BINMODE ? Qtrue : Qfalse;
}

#close_on_exec=(bool) ⇒ Boolean (rw)

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.

[ GitHub ]

  
# File 'io.c', line 4440

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?Boolean (rw)

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
[ GitHub ]

  
# File 'io.c', line 4392

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;
}

#closed?Boolean (readonly)

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
[ GitHub ]

  
# File 'io.c', line 4897

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 0 <= fptr->fd ? Qfalse : Qtrue;
}

#eofBoolean (readonly) #eof?Boolean
Also known as: #eof?

Returns true if ios is at end of file that means there are no more data to read. The stream must be opened for reading or an ::IOError will be raised.

f = File.new("testfile")
dummy = f.readlines
f.eof   #=> true

If ios is a stream such as pipe or socket, #eof? 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 blocking

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

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

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

[ GitHub ]

  
# File 'io.c', line 2128

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 defined(RUBY_TEST_CRLF_ENVIRONMENT) || defined(_WIN32)
    if (!NEED_READCONV(fptr) && NEED_NEWLINE_DECORATOR_ON_READ(fptr)) {
	return eof(fptr->fd) ? Qtrue : Qfalse;
    }
#endif
    if (io_fillbuf(fptr) < 0) {
	return Qtrue;
    }
    return Qfalse;
}

#eofBoolean (readonly) #eof?Boolean

Alias for #eof.

#isattyBoolean (readonly) #tty?Boolean

Alias for #tty?.

#linenoInteger (rw)

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
[ GitHub ]

  
# File 'io.c', line 3647

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 (rw)

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
[ GitHub ]

  
# File 'io.c', line 3674

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;
}

#posInteger (rw) #tellInteger
Also known as: #tell

Returns the current offset (in bytes) of ios.

f = File.new("testfile")
f.pos    #=> 0
f.gets   #=> "This is line one\n"
f.pos    #=> 17
[ GitHub ]

  
# File 'io.c', line 1901

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=(integer) ⇒ Integer (rw)

Seeks to the given position (in bytes) in ios. It is not guaranteed that seeking to the right position when ios is textmode.

f = File.new("testfile")
f.pos = 17
f.gets   #=> "This is line two\n"
[ GitHub ]

  
# File 'io.c', line 1995

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);
}

#syncBoolean (rw)

Returns the current “sync mode'' of ios. 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.new("testfile")
f.sync   #=> false
[ GitHub ]

  
# File 'io.c', line 2163

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

    io = GetWriteIO(io);
    GetOpenFile(io, fptr);
    return (fptr->mode & FMODE_SYNC) ? Qtrue : Qfalse;
}

#sync=(boolean) ⇒ Boolean (rw)

Sets the “sync mode'' to true or false. When sync mode is true, all output is immediately flushed to the underlying operating system and is not buffered internally. Returns the new state. See also #fsync.

f = File.new("testfile")
f.sync = true
[ GitHub ]

  
# File 'io.c', line 2188

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;
}

#posInteger (readonly) #tellInteger

Alias for #pos.

#isattyBoolean (readonly) #tty?Boolean
Also known as: #isatty

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

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

  
# File 'io.c', line 4366

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

    GetOpenFile(io, fptr);
    if (isatty(fptr->fd) == 0)
	return Qfalse;
    return Qtrue;
}

Instance Method Details

#<<(obj) ⇒ IO

::String Output—Writes obj to ios. obj will be converted to a string using to_s.

$stdout << "Hello " << "world!\n"

produces:

Hello world!
[ GitHub ]

  
# File 'io.c', line 1822

VALUE
rb_io_addstr(VALUE io, VALUE str)
{
    rb_io_write(io, str);
    return io;
}

#__read_nonblock(length, str, ex) (private)

This method is for internal use only.
[ GitHub ]

  
# File 'io.c', line 2943

static VALUE
io_read_nonblock(VALUE io, VALUE length, VALUE str, VALUE ex)
{
    rb_io_t *fptr;
    long n, len;
    struct io_internal_read_struct iis;
    int shrinkable;

    if ((len = NUM2LONG(length)) < 0) {
	rb_raise(rb_eArgError, "negative length %ld given", len);
    }

    shrinkable = io_setstrbuf(&str, len);
    OBJ_TAINT(str);
    rb_bool_expected(ex, "exception");

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

    if (len == 0)
	return str;

    n = read_buffered_data(RSTRING_PTR(str), len, fptr);
    if (n <= 0) {
	rb_io_set_nonblock(fptr);
	shrinkable |= io_setstrbuf(&str, len);
        iis.fd = fptr->fd;
        iis.nonblock = 1;
        iis.buf = RSTRING_PTR(str);
        iis.capa = len;
        n = read_internal_locktmp(str, &iis);
        if (n < 0) {
	    int e = errno;
	    if ((e == EWOULDBLOCK || e == EAGAIN)) {
                if (!ex) return sym_wait_readable;
		rb_readwrite_syserr_fail(RB_IO_WAIT_READABLE,
					 e, "read would block");
            }
            rb_syserr_fail_path(e, fptr->pathv);
        }
    }
    io_set_read_length(str, n, shrinkable);

    if (n == 0) {
        if (!ex) return Qnil;
	rb_eof_error();
    }

    return str;
}

#__write_nonblock(str, ex) (private)

This method is for internal use only.
[ GitHub ]

  
# File 'io.c', line 2995

static VALUE
io_write_nonblock(VALUE io, VALUE str, VALUE ex)
{
    rb_io_t *fptr;
    long n;

    if (!RB_TYPE_P(str, T_STRING))
	str = rb_obj_as_string(str);
    rb_bool_expected(ex, "exception");

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

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

    rb_io_set_nonblock(fptr);
    n = write(fptr->fd, RSTRING_PTR(str), RSTRING_LEN(str));
    RB_GC_GUARD(str);

    if (n < 0) {
	int e = errno;
	if (e == EWOULDBLOCK || e == EAGAIN) {
            if (!ex) {
		return sym_wait_writable;
	    }
	    else {
		rb_readwrite_syserr_fail(RB_IO_WAIT_WRITABLE, e, "write would block");
	    }
	}
	rb_syserr_fail_path(e, fptr->pathv);
    }

    return LONG2FIX(n);
}

#advise(advice, offset = 0, len = 0) ⇒ nil

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.

[ GitHub ]

  
# File 'io.c', line 9379

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
}

#bytes

This is a deprecated alias for #each_byte.

[ GitHub ]

  
# File 'io.c', line 3856

static VALUE
rb_io_bytes(VALUE io)
{
    rb_warn("IO#bytes is deprecated; use #each_byte instead");
    if (!rb_block_given_p())
	return rb_enumeratorize(io, ID2SYM(rb_intern("each_byte")), 0, 0);
    return rb_io_each_byte(io);
}

#chars

This is a deprecated alias for #each_char.

[ GitHub ]

  
# File 'io.c', line 4010

static VALUE
rb_io_chars(VALUE io)
{
    rb_warn("IO#chars is deprecated; use #each_char instead");
    if (!rb_block_given_p())
	return rb_enumeratorize(io, ID2SYM(rb_intern("each_char")), 0, 0);
    return rb_io_each_char(io);
}

#closenil

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 .popen, #close sets $?.

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

[ GitHub ]

  
# File 'io.c', line 4837

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_readnil

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.

[ GitHub ]

  
# File 'io.c', line 4936

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_writenil

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.

[ GitHub ]

  
# File 'io.c', line 4998

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;
}

#codepoints

This is a deprecated alias for #each_codepoint.

[ GitHub ]

  
# File 'io.c', line 4138

static VALUE
rb_io_codepoints(VALUE io)
{
    rb_warn("IO#codepoints is deprecated; use #each_codepoint instead");
    if (!rb_block_given_p())
	return rb_enumeratorize(io, ID2SYM(rb_intern("each_codepoint")), 0, 0);
    return rb_io_each_codepoint(io);
}

#each(sep = $/[, getline_args]) {|line| ... } ⇒ IO #each(limit[, getline_args]) {|line| ... } ⇒ IO #each(sep, limit[, getline_args]) {|line| ... } ⇒ IO #each(...) ⇒ Enumerator
Also known as: #each_line

ios.each_line(sep=$/ [, getline_args]) {|line| block } -> ios

ios.each_line(limit [, getline_args])      {|line| block } -> ios
ios.each_line(sep, limit [, getline_args]) {|line| block } -> ios
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 .readlines for details about getline_args.

[ GitHub ]

  
# File 'io.c', line 3785

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| ... } ⇒ IO #each_byteEnumerator

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
[ GitHub ]

  
# File 'io.c', line 3831

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));
	    errno = 0;
	}
	rb_io_check_byte_readable(fptr);
	READ_CHECK(fptr);
    } while (io_fillbuf(fptr) >= 0);
    return io;
}

#each_char {|c| ... } ⇒ IO #each_charEnumerator

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>
[ GitHub ]

  
# File 'io.c', line 3987

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| ... } ⇒ IO #codepoints {|c| ... } ⇒ IO #each_codepointEnumerator #codepointsEnumerator

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.

[ GitHub ]

  
# File 'io.c', line 4035

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.ptrfptr->cbuf.offfptr->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.ptrfptr->cbuf.offfptr->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));
	}
    }
    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.ptrfptr->rbuf.offfptr->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.ptrfptr->rbuf.offfptr->rbuf.len, enc);
	    fptr->rbuf.off += n;
	    fptr->rbuf.len -= n;
	    rb_yield(UINT2NUM(c));
	}
	else if (MBCLEN_INVALID_P(r)) {
	  invalid:
	    rb_raise(rb_eArgError, "invalid byte sequence in %s", rb_enc_name(enc));
	}
	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;
	}
    }
    return io;
}

#each(sep = $/[, getline_args]) {|line| ... } ⇒ IO #each(limit[, getline_args]) {|line| ... } ⇒ IO #each(sep, limit[, getline_args]) {|line| ... } ⇒ IO #each(...) ⇒ Enumerator

Alias for #each.

#external_encodingEncoding

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

[ GitHub ]

  
# File 'io.c', line 11689

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

    GetOpenFile(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

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.

[ GitHub ]

  
# File 'io.c', line 9965

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);
}

#fdatasync0?

Immediately writes all buffered data in ios to disk.

If the underlying operating system does not support fdatasync(2), #fsync is called instead (which might raise a ::NotImplementedError).

[ GitHub ]

  
# File 'io.c', line 2266

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(0);

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

    /* fall back */
    return rb_io_fsync(io);
}

#filenoInteger #to_iInteger

Alias for #to_i.

#flushIO

Flushes any buffered data within ios to the underlying operating system (note that this is Ruby internal buffering only; the OS may buffer the data as well).

$stdout.print "no newline"
$stdout.flush

produces:

no newline
[ GitHub ]

  
# File 'io.c', line 1882

VALUE
rb_io_flush(VALUE io)
{
    return rb_io_flush_raw(io, 1);
}

#fsync0?

Immediately writes all buffered data in ios to disk. Note that #fsync differs from using #sync=. The latter ensures that data is flushed from Ruby's buffers, but does not guarantee that the underlying operating system actually writes it to disk.

::NotImplementedError is raised if the underlying operating system does not support fsync(2).

[ GitHub ]

  
# File 'io.c', line 2217

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(0);
    if ((int)rb_thread_io_blocking_region(nogvl_fsync, fptr, fptr->fd) < 0)
	rb_sys_fail_path(fptr->pathv);
    return INT2FIX(0);
}

#getbyteInteger?

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
[ GitHub ]

  
# File 'io.c', line 4209

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

    GetOpenFile(io, fptr);
    rb_io_check_byte_readable(fptr);
    READ_CHECK(fptr);
    if (fptr->fd == 0 && (fptr->mode & FMODE_TTY) && RB_TYPE_P(rb_stdout, T_FILE)) {
        rb_io_t *ofp;
        GetOpenFile(rb_stdout, ofp);
        if (ofp->mode & FMODE_TTY) {
            rb_io_flush(rb_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);
}

#getcString?

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"
[ GitHub ]

  
# File 'io.c', line 4160

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_args]) ⇒ String? #gets(limit[, getline_args]) ⇒ String? #gets(sep, limit[, getline_args]) ⇒ String?

Reads the next “line'' from the I/O stream; lines are separated by sep. A separator of nil reads the entire contents, and a zero-length separator reads the input a paragraph at a time (two successive newlines in the input separate paragraphs). The stream must be opened for reading or an ::IOError will be raised. The line read in will be returned and also assigned to $_. Returns nil if called at end of file. If the first argument is an integer, or optional second argument is given, the returning string would not be longer than the given value in bytes.

File.new("testfile").gets   #=> "This is line one\n"
$_                          #=> "This is line one\n"

File.new("testfile").gets(4)#=> "This"

If IO contains multibyte characters byte then gets(1) returns character entirely:

# Russian characters take 2 bytes
File.write("testfile", "\u{442 435 441 442}")
File.open("testfile") {|f|f.gets(1)} #=> "\u0442"
File.open("testfile") {|f|f.gets(2)} #=> "\u0442"
File.open("testfile") {|f|f.gets(3)} #=> "\u0442\u0435"
File.open("testfile") {|f|f.gets(4)} #=> "\u0442\u0435"
[ GitHub ]

  
# File 'io.c', line 3614

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;
}

#initialize_copy(io)

This method is for internal use only.
[ GitHub ]

  
# File 'io.c', line 7455

static VALUE
rb_io_init_copy(VALUE dest, VALUE io)
{
    rb_io_t *fptr, *orig;
    int fd;
    VALUE write_io;
    off_t pos;

    io = rb_io_get_io(io);
    if (!OBJ_INIT_COPY(dest, io)) return dest;
    GetOpenFile(io, orig);
    MakeOpenFile(dest, fptr);

    rb_io_flush(io);

    /* copy rb_io_t structure */
    fptr->mode = orig->mode & ~FMODE_PREP;
    fptr->encs = orig->encs;
    fptr->pid = orig->pid;
    fptr->lineno = orig->lineno;
    if (!NIL_P(orig->pathv)) fptr->pathv = orig->pathv;
    fptr_copy_finalizer(fptr, orig);

    fd = ruby_dup(orig->fd);
    fptr->fd = fd;
    pos = io_tell(orig);
    if (0 <= pos)
        io_seek(fptr, pos, SEEK_SET);
    if (fptr->mode & FMODE_BINMODE) {
	rb_io_binmode(dest);
    }

    write_io = GetWriteIO(io);
    if (io != write_io) {
        write_io = rb_obj_dup(write_io);
        fptr->tied_io_for_writing = write_io;
        rb_ivar_set(dest, rb_intern("@tied_io_for_writing"), write_io);
    }

    return dest;
}

#inspectString

Return a string describing this IO object.

[ GitHub ]

  
# File 'io.c', line 2350

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_encodingEncoding

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

[ GitHub ]

  
# File 'io.c', line 11714

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

    GetOpenFile(io, fptr);
    if (!fptr->encs.enc2) return Qnil;
    return rb_enc_from_encoding(io_read_encoding(fptr));
}

#ioctl(integer_cmd, arg) ⇒ Integer

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.

[ GitHub ]

  
# File 'io.c', line 9871

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);
}

#lines(*args)

This is a deprecated alias for #each_line.

[ GitHub ]

  
# File 'io.c', line 3805

static VALUE
rb_io_lines(int argc, VALUE *argv, VALUE io)
{
    rb_warn("IO#lines is deprecated; use #each_line instead");
    if (!rb_block_given_p())
	return rb_enumeratorize(io, ID2SYM(rb_intern("each_line")), argc, argv);
    return rb_io_each_line(argc, argv, io);
}

#pidInteger

Returns the process ID of a child process associated with ios. This will be set by .popen.

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

produces:

In child, pid is 26209
In parent, child pid is 26209
[ GitHub ]

  
# File 'io.c', line 2331

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

    GetOpenFile(io, fptr);
    if (!fptr->pid)
	return Qnil;
    return PIDT2NUM(fptr->pid);
}

#pread(maxlen, offset[, outbuf]) ⇒ String

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 #seek and #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
[ GitHub ]

  
# File 'io.c', line 5229

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();
    }
    OBJ_TAINT(str);

    return str;
}

#printf(format_string[, obj, ...]) ⇒ nil

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

[ GitHub ]

  
# File 'io.c', line 7505

VALUE
rb_io_printf(int argc, const VALUE *argv, VALUE out)
{
    rb_io_write(out, rb_f_sprintf(argc, argv));
    return Qnil;
}

#putc(obj) ⇒ Object

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
[ GitHub ]

  
# File 'io.c', line 7648

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

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 ($\).

[ GitHub ]

  
# File 'io.c', line 7747

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

Writes the given string to ios at offset using pwrite() system call. This is advantageous to combining #seek and #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"
[ GitHub ]

  
# File 'io.c', line 5298

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([length [, outbuf]]) ⇒ String, ...

Reads length bytes from the I/O stream.

length must be a non-negative integer or nil.

If length is a positive integer, read tries to read length bytes without any conversion (binary mode). It returns nil if an EOF is encountered before anything can be read. Fewer than length bytes are returned if an EOF is encountered during the read. In the case of an integer length, the resulting string is always in ASCII-8BIT encoding.

If length is omitted or is nil, it reads until EOF and the encoding conversion is applied, if applicable. A string is returned even if EOF is encountered before any data is read.

If length is zero, it returns an empty string ("").

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.

When this method is called at end of file, it returns nil or "", depending on length: read, read(nil), and read(0) return "", read(positive_integer) returns nil.

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

# read whole file
open("file") do |f|
  data = f.read   # This returns a string even if the file is empty.
  # ...
end

# iterate over fixed length records
open("fixed-record-file") do |f|
  while record = f.read(256)
    # ...
  end
end

# iterate over variable length records,
# each record is prefixed by its 32-bit length
open("variable-record-file") do |f|
  while len = f.read(4)
    len = len.unpack("N")[0]   # 32-bit length
    record = f.read(len)       # This returns a string even if len is 0.
  end
end

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 length (or until EOF). This behavior is preserved even if ios 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.

[ GitHub ]

  
# File 'io.c', line 3099

static VALUE
io_read(int argc, VALUE *argv, VALUE io)
{
    rb_io_t *fptr;
    long n, len;
    VALUE length, str;
    int shrinkable;
#if defined(RUBY_TEST_CRLF_ENVIRONMENT) || defined(_WIN32)
    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 defined(RUBY_TEST_CRLF_ENVIRONMENT) || defined(_WIN32)
    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 defined(RUBY_TEST_CRLF_ENVIRONMENT) || defined(_WIN32)
    if (previous_mode == O_TEXT) {
	setmode(fptr->fd, O_TEXT);
    }
#endif
    if (n == 0) return Qnil;
    OBJ_TAINT(str);

    return str;
}

#read_nonblock(maxlen[, options]) ⇒ String #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.

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 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.

[ GitHub ]

  
# File 'prelude.rb', line 72

def read_nonblock(len, buf = nil, exception: true)
  __read_nonblock(len, buf, exception)
end

#readbyteInteger

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

[ GitHub ]

  
# File 'io.c', line 4242

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

    if (NIL_P(c)) {
	rb_eof_error();
    }
    return c;
}

#readcharString

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

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

  
# File 'io.c', line 4186

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 #readline(limit[, getline_args]) ⇒ String #readline(sep, limit[, getline_args]) ⇒ String

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

[ GitHub ]

  
# File 'io.c', line 3694

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 #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 .readlines for details about getline_args.

[ GitHub ]

  
# File 'io.c', line 3731

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 #readpartial(maxlen, outbuf) ⇒ outbuf

Reads at most maxlen bytes from the I/O stream. It blocks only if ios has no data immediately available. It doesn't block if some data available.

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.

It raises ::EOFError on end of file.

readpartial is designed for streams such as pipe, socket, tty, etc. It blocks only when no data immediately available. This means that it blocks only when following all conditions hold.

  • the byte buffer in the IO object is empty.

  • the content of the stream is empty.

  • the stream is not reached to EOF.

When readpartial blocks, it waits data or EOF on the stream. If some data is reached, readpartial returns with the data. If EOF is reached, readpartial raises ::EOFError.

When readpartial doesn't blocks, it returns or raises immediately. If the byte buffer is not empty, it returns the data in the buffer. Otherwise if the stream has some content, it returns the data in the stream. Otherwise if the stream is reached to EOF, it raises ::EOFError.

r, w = IO.pipe           #               buffer          pipe content
w << "abc"               #               ""              "abc".
r.readpartial(4096)      #=> "abc"       ""              ""
r.readpartial(4096)      # blocks because buffer and pipe is empty.

r, w = IO.pipe           #               buffer          pipe content
w << "abc"               #               ""              "abc"
w.close                  #               ""              "abc" EOF
r.readpartial(4096)      #=> "abc"       ""              EOF
r.readpartial(4096)      # raises EOFError

r, w = IO.pipe           #               buffer          pipe content
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"     ""              ""

Note that readpartial behaves 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 retry the system call.

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

[ GitHub ]

  
# File 'io.c', line 2922

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) ⇒ IO #reopen(path, mode[, opt]) ⇒ IO

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 .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"
[ GitHub ]

  
# File 'io.c', line 7366

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(0);
    }
    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;
}

#rewind0

Positions ios to the beginning of input, resetting #lineno to zero.

f = File.new("testfile")
f.readline   #=> "This is line one\n"
f.rewind     #=> 0
f.lineno     #=> 0
f.readline   #=> "This is line one\n"

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

[ GitHub ]

  
# File 'io.c', line 2027

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(amount, whence = IO::SEEK_SET) ⇒ 0

Seeks to a given offset anInteger in the stream according to the value of whence:

:CUR or IO::SEEK_CUR  | Seeks to _amount_ plus current position
----------------------+--------------------------------------------------
:END or IO::SEEK_END  | Seeks to _amount_ plus end of stream (you
                      | probably want a negative value for _amount_)
----------------------+--------------------------------------------------
:SET or IO::SEEK_SET  | Seeks to the absolute location given by _amount_

Example:

f = File.new("testfile")
f.seek(-13, IO::SEEK_END)   #=> 0
f.readline                  #=> "And so on...\n"
[ GitHub ]

  
# File 'io.c', line 1969

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 #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.

[ GitHub ]

  
# File 'io.c', line 11743

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 rb_funcallv(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_bomEncoding?

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
[ GitHub ]

  
# File 'io.c', line 8326

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");
    }
    if (!io_set_encoding_by_bom(io)) return Qnil;
    return rb_enc_from_encoding(fptr->encs.enc);
}

#statstat

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
[ GitHub ]

  
# File 'file.c', line 1319

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);
}

#sysread(maxlen[, outbuf]) ⇒ String

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"
[ GitHub ]

  
# File 'io.c', line 5131

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");
    }

    /*
     * FIXME: removing rb_thread_wait_fd() here changes sysread semantics
     * on non-blocking IOs.  However, it's still currently possible
     * for sysread to raise Errno::EAGAIN if another thread read()s
     * the IO after we return from rb_thread_wait_fd() but before
     * we call read()
     */
    rb_thread_wait_fd(fptr->fd);

    rb_io_check_closed(fptr);

    io_setstrbuf(&str, ilen);
    iis.fd = fptr->fd;
    iis.nonblock = 1; /* for historical reasons, maybe (see above) */
    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();
    }
    OBJ_TAINT(str);

    return str;
}

#sysseek(offset, whence = IO::SEEK_SET) ⇒ Integer

Seeks to a given offset in the stream according to the value of whence (see #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."
[ GitHub ]

  
# File 'io.c', line 5044

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

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
[ GitHub ]

  
# File 'io.c', line 5084

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->fd, ptr, len);
    if (n < 0) rb_sys_fail_path(fptr->pathv);
    rb_str_tmp_frozen_release(str, tmp);

    return LONG2FIX(n);
}

#filenoInteger #to_iInteger
Also known as: #fileno

Returns an integer representing the numeric file descriptor for ios.

$stdin.fileno    #=> 0
$stdout.fileno   #=> 1
[ GitHub ]

  
# File 'io.c', line 2299

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);
}

#to_ioIO

Returns ios.

[ GitHub ]

  
# File 'io.c', line 2386

static VALUE
rb_io_to_io(VALUE io)
{
    return io;
}

#ungetbyte(string) ⇒ nil #ungetbyte(integer) ⇒ nil

Pushes back bytes (passed as a parameter) onto ios, such that a subsequent buffered read will return it. Only one byte may be pushed back before a subsequent read operation (that is, you will be able to read only the last of several bytes that have been pushed back). Has no effect with unbuffered reads (such as #sysread).

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

  
# File 'io.c', line 4270

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(string) ⇒ nil

Pushes back one character (passed as a parameter) onto ios, such that a subsequent buffered character read will return it. Only one character may be pushed back before a subsequent read operation (that is, you will be able to read only the last of several characters that have been pushed back). Has no effect with unbuffered reads (such as #sysread).

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

  
# File 'io.c', line 4309

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

    GetOpenFile(io, fptr);
    rb_io_check_char_readable(fptr);
    if (NIL_P(c)) return Qnil;
    if (FIXNUM_P(c)) {
	c = rb_enc_uint_chr(FIX2UINT(c), io_read_encoding(fptr));
    }
    else if (RB_TYPE_P(c, T_BIGNUM)) {
	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(string, ...) ⇒ Integer

Writes the given strings to ios. The stream must be opened for writing. Arguments that are not a string will be converted to a string using to_s. Returns the number of bytes written in total.

count = $stdout.write("This is", " a test\n")
puts "That was #{count} bytes of data"

produces:

This is a test
That was 15 bytes of data
[ GitHub ]

  
# File 'io.c', line 1771

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 #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.

[ GitHub ]

  
# File 'prelude.rb', line 130

def write_nonblock(buf, exception: true)
  __write_nonblock(buf, exception)
end