Class: IO

Inherits:
Object show all
Includes:
Enumerable, File::Constants
Defined in:
io.c

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

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

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

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

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

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

io/console

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

Requiring io/console adds the following methods:

  • IO::console

  • IO#raw

  • IO#raw!

  • IO#cooked

  • IO#cooked!

  • IO#getch

  • IO#echo=

  • IO#echo?

  • IO#noecho

  • IO#winsize

  • IO#winsize=

  • IO#iflush

  • IO#ioflush

  • IO#oflush

Example:

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

Direct Known Subclasses

File

Defined Under Namespace

Modules: WaitReadable, WaitWritable Classes: EAGAINWaitReadable, EAGAINWaitWritable, EINPROGRESSWaitReadable, EINPROGRESSWaitWritable, EWOULDBLOCKWaitReadable, EWOULDBLOCKWaitWritable

Constant Summary collapse

SEEK_SET =

Set I/O position from the beginning

INT2FIX(SEEK_SET)
SEEK_CUR =

Set I/O position from the current position

INT2FIX(SEEK_CUR)
SEEK_END =

Set I/O position from the end

INT2FIX(SEEK_END)
SEEK_DATA =

Set I/O position to the next location containing data

INT2FIX(SEEK_DATA)
SEEK_HOLE =

Set I/O position to the next hole

INT2FIX(SEEK_HOLE)

Constants included from File::Constants

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

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Enumerable

#all?, #any?, #chain, #chunk, #chunk_while, #collect, #collect_concat, #count, #cycle, #detect, #drop, #drop_while, #each_cons, #each_entry, #each_slice, #each_with_index, #each_with_object, #entries, #filter, #filter_map, #find, #find_all, #find_index, #first, #flat_map, #grep, #grep_v, #group_by, #include?, #inject, #lazy, #map, #max, #max_by, #member?, #min, #min_by, #minmax, #minmax_by, #none?, #one?, #partition, #reduce, #reject, #reverse_each, #select, #slice_after, #slice_before, #slice_when, #sort, #sort_by, #sum, #take, #take_while, #tally, #to_a, #to_h, #uniq, #zip

Constructor Details

#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 IO.sysopen and IO.for_fd.

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

Open Mode

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

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

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

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

IO Open Mode

Ruby allows the following open modes:

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

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

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

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

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

“a+” Read-write, each write call appends data at end of file.

Creates a new file for reading and writing if file does
not exist.

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

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

“t” Text file mode

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

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

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

IO Encoding

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

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

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

Options

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

:mode

Same as mode parameter

:flags

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

:external_encoding

External encoding for the IO.

:internal_encoding

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

If the value is nil no conversion occurs.

:encoding

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

:textmode

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

:binmode

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

:autoclose

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

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

Example 1

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

Produces:

Hello
World

Example 2

require 'fcntl'

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

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

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


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# File 'io.c', line 8265

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 "

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# File 'io.c', line 10618

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


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# File 'io.c', line 10767

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

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

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

This method returns the number of bytes copied.

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

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

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

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


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# File 'io.c', line 11668

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 IO.new.


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# File 'io.c', line 8428

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(...) ⇒ Object

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

Overloads:

  • .foreach(name, sep = $/[, getline_args, open_args]) {|line| ... } ⇒ nil

    Yields:

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

    Yields:

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

    Yields:

    • (line)

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# File 'io.c', line 10445

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

    argc = rb_scan_args(argc, argv, "13:", NULL, NULL, NULL, NULL, &opt);
    RETURN_ENUMERATOR(self, orig_argc, argv);
    extract_getline_args(argc-1, argv+1, &garg);
    open_key_args(self, argc, argv, opt, &arg);
    if (NIL_P(arg.io)) return Qnil;
    extract_getline_opts(opt, &garg);
    check_getline_args(&garg.rs, &garg.limit, garg.io = arg.io);
    return rb_ensure(io_s_foreach, (VALUE)&garg, rb_io_close, arg.io);
}

.new(*args) ⇒ Object

:nodoc:


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# File 'io.c', line 8407

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_kw(argc, argv, klass, RB_PASS_CALLED_KEYWORDS);
}

.open(*args) ⇒ Object

call-seq:

IO.open(fd, mode="r" [, opt])                -> io
IO.open(fd, mode="r" [, opt]) {|io| block }  -> obj

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

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


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# File 'io.c', line 7042

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

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

    return io;
}

.pipeArray .pipe(ext_enc) ⇒ Array .pipe("ext_enc: int_enc"[, opt]) ⇒ Array .pipe(ext_enc, int_enc[, opt]) ⇒ Array

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>

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# File 'io.c', line 10286

static VALUE
rb_io_s_pipe(int argc, VALUE *argv, VALUE klass)
{
    int pipes[2], state;
    VALUE r, w, args[3], v1, v2;
    VALUE opt;
    rb_io_t *fptr, *fptr2;
    struct io_encoding_set_args ies_args;
    int fmode = 0;
    VALUE ret;

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

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

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

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

    extract_binmode(opt, &fmode);

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

#if DEFAULT_TEXTMODE
    if ((fptr->mode & FMODE_TEXTMODE) && (fmode & FMODE_BINMODE)) {
	fptr->mode &= ~FMODE_TEXTMODE;
	setmode(fptr->fd, O_BINARY);
    }
#if 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 IO#pid method.

cmd is a string or an array as follows.

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

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

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

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

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

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

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

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

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

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

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

produces:

["Linux\n"]
Parent is 21346
Thu Jan 15 22:41:19 JST 2009
21346 is here, f is #<IO:fd 3>
21352 is here, f is nil
#<Process::Status: pid 21352 exit 0>
<foo>bar;zot;

Overloads:

  • .popen([env,], mode = "r"[, opt]) {|io| ... } ⇒ Object

    Yields:

    • (io)

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# File 'io.c', line 6902

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"

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# File 'io.c', line 10579

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 IO.read for details about open_args.


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# File 'io.c', line 10500

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?

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

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

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

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

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

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

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

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

However, several more complicated situations exist.

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

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

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

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

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

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

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

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

Parameters

read_array

an array of IO objects that wait until ready for read

write_array

an array of IO objects that wait until ready for write

error_array

an array of IO objects that wait for exceptions

timeout

a numeric value in second

Example

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

produces:

ping pong
ping pong
ping pong
(snipped)
ping

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# File 'io.c', line 9563

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

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

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

    return rb_ensure(select_call, (VALUE)&args, select_end, (VALUE)&args);
}

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

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

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

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# File 'io.c', line 7064

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

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

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

    RB_GC_GUARD(fname) = rb_str_new4(fname);
    fd = rb_sysopen(fname, oflags, perm);
    return INT2NUM(fd);
}

.try_convert(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>

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# File 'io.c', line 805

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.


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# File 'io.c', line 10752

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

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!

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# File 'io.c', line 1859

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

#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.


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# File 'io.c', line 9399

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

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

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

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

#ifdef HAVE_POSIX_FADVISE
    return do_io_advise(fptr, advice, off, l);
#else
    ((void)off, (void)l);	/* Ignore all hint */
    return Qnil;
#endif
}

#autoclose=(bool) ⇒ Boolean

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

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# File 'io.c', line 8469

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

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


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# File 'io.c', line 8444

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

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


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# File 'io.c', line 5419

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

Returns true if ios is binmode.


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# File 'io.c', line 5438

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

#bytesObject

This is a deprecated alias for #each_byte.


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# File 'io.c', line 3878

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

#charsObject

This is a deprecated alias for #each_char.


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# File 'io.c', line 4032

static VALUE
rb_io_chars(VALUE io)
{
    rb_warn_deprecated("IO#chars", "#each_char");
    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 IO.popen, #close sets $?.

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


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# File 'io.c', line 4859

static VALUE
rb_io_close_m(VALUE io)
{
    rb_io_t *fptr = rb_io_get_fptr(io);
    if (fptr->fd < 0) {
        return Qnil;
    }
    rb_io_close(io);
    return Qnil;
}

#close_on_exec=(bool) ⇒ Boolean

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.


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# File 'io.c', line 4462

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

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

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# File 'io.c', line 4414

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

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

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

#close_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.


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# File 'io.c', line 4958

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.


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# File 'io.c', line 5020

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

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

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

    if (io != write_io) {
	fptr = rb_io_get_fptr(rb_io_taint_check(io));
	fptr->tied_io_for_writing = 0;
    }
    rb_io_close(write_io);
    return Qnil;
}

#closed?Boolean

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

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# File 'io.c', line 4919

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;
}

#codepointsObject

This is a deprecated alias for #each_codepoint.


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# File 'io.c', line 4160

static VALUE
rb_io_codepoints(VALUE io)
{
    rb_warn_deprecated("IO#codepoints", "#each_codepoint");
    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(...) ⇒ Object

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 IO.readlines for details about getline_args.

Overloads:

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

    Yields:

    • (line)
  • #each(limit[, getline_args]) {|line| ... } ⇒ IO

    Yields:

    • (line)
  • #each(sep, limit[, getline_args]) {|line| ... } ⇒ IO

    Yields:

    • (line)

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# File 'io.c', line 3807

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_byteObject

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

Overloads:

  • #each_byte {|byte| ... } ⇒ IO

    Yields:

    • (byte)

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# File 'io.c', line 3853

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_charObject

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>

Overloads:

  • #each_char {|c| ... } ⇒ IO

    Yields:

    • (c)

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# File 'io.c', line 4009

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_codepointObject #codepointsObject

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.

Overloads:

  • #each_codepoint {|c| ... } ⇒ IO

    Yields:

    • (c)
  • #codepoints {|c| ... } ⇒ IO

    Yields:

    • (c)

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# File 'io.c', line 4057

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

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

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

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 IO.readlines for details about getline_args.

Overloads:

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

    Yields:

    • (line)
  • #each(limit[, getline_args]) {|line| ... } ⇒ IO

    Yields:

    • (line)
  • #each(sep, limit[, getline_args]) {|line| ... } ⇒ IO

    Yields:

    • (line)

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# File 'io.c', line 3807

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;
}

#eofBoolean #eof?Boolean

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


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# File 'io.c', line 2165

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 #eof?Boolean

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


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# File 'io.c', line 2165

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;
}

#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.


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# File 'io.c', line 11704

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.


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# File 'io.c', line 9985

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), IO#fsync is called instead (which might raise a NotImplementedError).


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# File 'io.c', line 2303

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 Also known as: to_i

Returns an integer representing the numeric file descriptor for ios.

$stdin.fileno    #=> 0
$stdout.fileno   #=> 1

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# File 'io.c', line 2336

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);
}

#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

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# File 'io.c', line 1919

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 IO#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).


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# File 'io.c', line 2254

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

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# File 'io.c', line 4231

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"

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# File 'io.c', line 4182

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"

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# File 'io.c', line 3636

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) ⇒ Object

:nodoc:


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# File 'io.c', line 7471

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.


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# File 'io.c', line 2387

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.


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# File 'io.c', line 11729

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.


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# File 'io.c', line 9891

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);
}

#isattyBoolean #tty?Boolean

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

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

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# File 'io.c', line 4388

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

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

#linenoInteger

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

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# File 'io.c', line 3669

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

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

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# File 'io.c', line 3696

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;
}

#lines(*args) ⇒ Object

This is a deprecated alias for #each_line.


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# File 'io.c', line 3827

static VALUE
rb_io_lines(int argc, VALUE *argv, VALUE io)
{
    rb_warn_deprecated("IO#lines", "#each_line");
    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 IO.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

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# File 'io.c', line 2368

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

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

#posInteger #tellInteger

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

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# File 'io.c', line 1938

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

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"

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# File 'io.c', line 2032

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

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

    return OFFT2NUM(pos);
}

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

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

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

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# File 'io.c', line 5250

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

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

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

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

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

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

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

    return str;
}

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

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

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

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

produces:

This is 100 percent.

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# File 'io.c', line 7592

VALUE
rb_io_print(int argc, const VALUE *argv, VALUE out)
{
    int i;
    VALUE line;

    /* if no argument given, print `$_' */
    if (argc == 0) {
	argc = 1;
	line = rb_lastline_get();
	argv = &line;
    }
    for (i=0; i<argc; i++) {
	if (!NIL_P(rb_output_fs) && i>0) {
	    rb_io_write(out, rb_output_fs);
	}
	rb_io_write(out, argv[i]);
    }
    if (argc > 0 && !NIL_P(rb_output_rs)) {
	rb_io_write(out, rb_output_rs);
    }

    return Qnil;
}

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

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


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# File 'io.c', line 7521

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

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# File 'io.c', line 7664

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 ($\).


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# File 'io.c', line 7763

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

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

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

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# File 'io.c', line 5318

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.


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# File 'io.c', line 3122

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;

    return str;
}

#readbyteInteger

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


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# File 'io.c', line 4264

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"

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# File 'io.c', line 4208

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 IO#gets, but raises an EOFError on end of file.


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# File 'io.c', line 3716

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 IO.readlines for details about getline_args.


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# File 'io.c', line 3753

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) ⇒ Object

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 IO#sysread causes Errno::EWOULDBLOCK as if the fd is blocking mode.


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# File 'io.c', line 2946

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 IO.open.

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

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# File 'io.c', line 7382

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.


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# File 'io.c', line 2064

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"

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# File 'io.c', line 2006

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.


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# File 'io.c', line 11758

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

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# File 'io.c', line 8342

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

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

#statObject

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

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# 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);
}

#syncBoolean

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 IO#fsync.

f = File.new("testfile")
f.sync   #=> false

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# File 'io.c', line 2200

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=(sync) ⇒ Object


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# File 'io.c', line 2271

static VALUE
rb_io_set_sync(VALUE io, VALUE sync)
{
    rb_notimplement();
    UNREACHABLE;
}

#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"

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# File 'io.c', line 5153

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();
    }

    return str;
}

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

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

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

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# File 'io.c', line 5066

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

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# File 'io.c', line 5106

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);
}

#posInteger #tellInteger

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

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# File 'io.c', line 1938

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

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

#to_ioIO

Returns ios.


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# File 'io.c', line 2423

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

#isattyBoolean #tty?Boolean

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

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

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# File 'io.c', line 4388

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

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

#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 IO#sysread).

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

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# File 'io.c', line 4292

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 IO#sysread).

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

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# File 'io.c', line 4331

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

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# File 'io.c', line 1808

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);
    }
}