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[DOC] Enhanced RDoc for IO (#6669)

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517
doc/io_streams.rdoc
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@ -1,517 +0,0 @@
== \IO Streams
This page describes:
- {Stream classes}[rdoc-ref:io_streams.rdoc@Stream+Classes].
- {Pre-existing streams}[rdoc-ref:io_streams.rdoc@Pre-Existing+Streams].
- {User-created streams}[rdoc-ref:io_streams.rdoc@User-Created+Streams].
- {Basic \IO}[rdoc-ref:io_streams.rdoc@Basic+IO], including:
- {Position}[rdoc-ref:io_streams.rdoc@Position].
- {Open and closed streams}[rdoc-ref:io_streams.rdoc@Open+and+Closed+Streams].
- {End-of-stream}[rdoc-ref:io_streams.rdoc@End-of-Stream].
- {Line \IO}[rdoc-ref:io_streams.rdoc@Line+IO], including:
- {Line separator}[rdoc-ref:io_streams.rdoc@Line+Separator].
- {Line limit}[rdoc-ref:io_streams.rdoc@Line+Limit].
- {Line number}[rdoc-ref:io_streams.rdoc@Line+Number].
- {Line options}[rdoc-ref:io_streams.rdoc@Line+Options].
- {Character \IO}[rdoc-ref:io_streams.rdoc@Character+IO].
- {Byte \IO}[rdoc-ref:io_streams.rdoc@Byte+IO].
- {Codepoint \IO}[rdoc-ref:io_streams.rdoc@Codepoint+IO].
=== Stream Classes
Ruby supports processing data as \IO streams;
that is, as data that may be read, re-read, written, re-written,
and traversed via iteration.
Core classes with such support include:
- IO, and its derived class File.
- {StringIO}[rdoc-ref:StringIO]: for processing a string.
- {ARGF}[rdoc-ref:ARGF]: for processing files cited on the command line.
Except as noted, the instance methods described on this page
are available in classes \ARGF, \File, \IO, and \StringIO.
A few, also noted, are available in class \Kernel.
=== Pre-Existing Streams
Pre-existing streams that are referenced by constants include:
- $stdin: read-only instance of \IO.
- $stdout: write-only instance of \IO.
- $stderr: read-only instance of \IO.
- \ARGF: read-only instance of \ARGF.
=== User-Created Streams
You can create streams:
- \File:
- File.new: returns a new \File object;
the file should be closed when no longer needed.
- File.open: passes a new \File object to given the block;
the file is automatically closed on block exit.
- \IO:
- IO.new: returns a new \IO object for the given integer file descriptor;
the \IO object should be closed when no longer needed.
- IO.open: passes a new \IO object to the given block;
the \IO object is automatically closed on block exit.
- IO.popen: returns a new \IO object that is connected to the $stdin
and $stdout of a newly-launched subprocess.
- Kernel#open: returns a new \IO object connected to a given source:
stream, file, or subprocess;
the \IO object should be closed when no longer needed.
- \StringIO:
- StringIO.new: returns a new \StringIO object;
the \StringIO object should be closed when no longer needed.
- StringIO.open: passes a new \StringIO object to the given block;
the \StringIO object is automatically closed on block exit.
(You cannot create an \ARGF object, but one already exists.)
=== About the Examples
Many examples here use these variables:
:include: doc/examples/files.rdoc
=== Basic \IO
You can perform basic stream \IO with these methods:
- IO#read: Returns all remaining or the next _n_ bytes read from the stream,
for a given _n_:
f = File.new('t.txt')
f.read # => "First line\nSecond line\n\nFourth line\nFifth line\n"
f.rewind
f.read(30) # => "First line\r\nSecond line\r\n\r\nFou"
f.read(30) # => "rth line\r\nFifth line\r\n"
f.read(30) # => nil
f.close
- IO#write: Writes one or more given strings to the stream:
$stdout.write('Hello', ', ', 'World!', "\n") # => 14
$stdout.write('foo', :bar, 2, "\n")
Output:
Hello, World!
foobar2
==== Position
An \IO stream has a nonnegative integer _position_,
which is the byte offset at which the next read or write is to occur.
A new stream has position zero (and line number zero);
method +rewind+ resets the position (and line number) to zero.
The relevant methods:
- IO#tell (aliased as +#pos+):
Returns the current position (in bytes) in the stream:
f = File.new('t.txt')
f.tell # => 0
f.gets # => "First line\n"
f.tell # => 12
f.close
- IO#pos=: Sets the position of the stream (in bytes):
f = File.new('t.txt')
f.tell # => 0
f.pos = 20 # => 20
f.tell # => 20
f.close
- IO#seek: Sets the position of the stream to a given integer +offset+
(in bytes), with respect to a given constant +whence+, which is one of:
- +:CUR+ or <tt>IO::SEEK_CUR</tt>:
Repositions the stream to its current position plus the given +offset+:
f = File.new('t.txt')
f.tell # => 0
f.seek(20, :CUR) # => 0
f.tell # => 20
f.seek(-10, :CUR) # => 0
f.tell # => 10
f.close
- +:END+ or <tt>IO::SEEK_END</tt>:
Repositions the stream to its end plus the given +offset+:
f = File.new('t.txt')
f.tell # => 0
f.seek(0, :END) # => 0 # Repositions to stream end.
f.tell # => 52
f.seek(-20, :END) # => 0
f.tell # => 32
f.seek(-40, :END) # => 0
f.tell # => 12
f.close
- +:SET+ or <tt>IO:SEEK_SET</tt>:
Repositions the stream to the given +offset+:
f = File.new('t.txt')
f.tell # => 0
f.seek(20, :SET) # => 0
f.tell # => 20
f.seek(40, :SET) # => 0
f.tell # => 40
f.close
- IO#rewind: Positions the stream to the beginning (also resetting the line number):
f = File.new('t.txt')
f.tell # => 0
f.gets # => "First line\n"
f.tell # => 12
f.rewind # => 0
f.tell # => 0
f.lineno # => 0
f.close
==== Open and Closed Streams
A new \IO stream may be open for reading, open for writing, or both.
A stream is automatically closed when claimed by the garbage collector.
Attempted reading or writing on a closed stream raises an exception.
- IO#close: Closes the stream for both reading and writing.
- IO#close_read: Closes the stream for reading; not in ARGF.
- IO#close_write: Closes the stream for writing; not in ARGF.
- IO#closed?: Returns whether the stream is closed.
==== End-of-Stream
You can query whether a stream is positioned at its end using
method IO#eof? (also aliased as +#eof+).
You can reposition to end-of-stream by reading all stream content:
f = File.new('t.txt')
f.eof? # => false
f.read # => "First line\nSecond line\n\nFourth line\nFifth line\n"
f.eof? # => true
Or by using method IO#seek:
f = File.new('t.txt')
f.eof? # => false
f.seek(0, :END)
f.eof? # => true
=== Line \IO
You can read an \IO stream line-by-line using these methods:
- IO#each_line: Passes each line to the block:
f = File.new('t.txt')
f.each_line {|line| p line }
Output:
"First line\n"
"Second line\n"
"\n"
"Fourth line\n"
"Fifth line\n"
The reading may begin mid-line:
f = File.new('t.txt')
f.pos = 27
f.each_line {|line| p line }
Output:
"rth line\n"
"Fifth line\n"
- IO#gets (also in Kernel): Returns the next line (which may begin mid-line):
f = File.new('t.txt')
f.gets # => "First line\n"
f.gets # => "Second line\n"
f.pos = 27
f.gets # => "rth line\n"
f.readlines # => ["Fifth line\n"]
f.gets # => nil
- IO#readline (also in Kernel; not in StringIO):
Like #gets, but raises an exception at end-of-stream.
- IO#readlines (also in Kernel): Returns all remaining lines in an array;
may begin mid-line:
f = File.new('t.txt')
f.pos = 19
f.readlines # => ["ine\n", "\n", "Fourth line\n", "Fifth line\n"]
f.readlines # => []
Each of these reader methods may be called with:
- An optional line separator, +sep+.
- An optional line-size limit, +limit+.
- Both +sep+ and +limit+.
You can write to an \IO stream line-by-line using this method:
- IO#puts (also in Kernel; not in \StringIO): Writes objects to the stream:
f = File.new('t.tmp', 'w')
f.puts('foo', :bar, 1, 2.0, Complex(3, 0))
f.flush
File.read('t.tmp') # => "foo\nbar\n1\n2.0\n3+0i\n"
==== Line Separator
The default line separator is the given by the global variable <tt>$/</tt>,
whose value is by default <tt>"\n"</tt>.
The line to be read next is all data from the current position
to the next line separator:
f = File.new('t.txt')
f.gets # => "First line\n"
f.gets # => "Second line\n"
f.gets # => "\n"
f.gets # => "Fourth line\n"
f.gets # => "Fifth line\n"
f.close
You can specify a different line separator:
f = File.new('t.txt')
f.gets('l') # => "First l"
f.gets('li') # => "ine\nSecond li"
f.gets('lin') # => "ne\n\nFourth lin"
f.gets # => "e\n"
f.close
There are two special line separators:
- +nil+: The entire stream is read into a single string:
f = File.new('t.txt')
f.gets(nil) # => "First line\nSecond line\n\nFourth line\nFifth line\n"
f.close
- <tt>''</tt> (the empty string): The next "paragraph" is read
(paragraphs being separated by two consecutive line separators):
f = File.new('t.txt')
f.gets('') # => "First line\nSecond line\n\n"
f.gets('') # => "Fourth line\nFifth line\n"
f.close
==== Line Limit
The line to be read may be further defined by an optional integer argument +limit+,
which specifies that the number of bytes returned may not be (much) longer
than the given +limit+;
a multi-byte character will not be split, and so a line may be slightly longer
than the given limit.
If +limit+ is not given, the line is determined only by +sep+.
# Text with 1-byte characters.
File.new('t.txt') {|f| f.gets(1) } # => "F"
File.new('t.txt') {|f| f.gets(2) } # => "Fi"
File.new('t.txt') {|f| f.gets(3) } # => "Fir"
File.new('t.txt') {|f| f.gets(4) } # => "Firs"
# No more than one line.
File.new('t.txt') {|f| f.gets(10) } # => "First line"
File.new('t.txt') {|f| f.gets(11) } # => "First line\n"
File.new('t.txt') {|f| f.gets(12) } # => "First line\n"
# Text with 2-byte characters, which will not be split.
File.new('r.rus') {|f| f.gets(1).size } # => 1
File.new('r.rus') {|f| f.gets(2).size } # => 1
File.new('r.rus') {|f| f.gets(3).size } # => 2
File.new('r.rus') {|f| f.gets(4).size } # => 2
==== Line Separator and Line Limit
With arguments +sep+ and +limit+ given,
combines the two behaviors:
- Returns the next line as determined by line separator +sep+.
- But returns no more bytes than are allowed by the limit.
Example:
File.new('t.txt') {|f| f.gets('li', 20) } # => "First li"
File.new('t.txt') {|f| f.gets('li', 2) } # => "Fi"
==== Line Number
A readable \IO stream has a _line_ _number_,
which is the non-negative integer line number
in the stream where the next read will occur.
The line number is the number of lines read by certain line-oriented methods
(IO.foreach, IO#each_line, IO#gets, IO#readline, and IO#readlines)
according to the given (or default) line separator +sep+.
A new stream is initially has line number zero (and position zero);
method +rewind+ resets the line number (and position) to zero.
\Method IO#lineno returns the line number.
Reading lines from a stream usually changes its line number:
f = File.new('t.txt', 'r')
f.lineno # => 0
f.readline # => "This is line one.\n"
f.lineno # => 1
f.readline # => "This is the second line.\n"
f.lineno # => 2
f.readline # => "Here's the third line.\n"
f.lineno # => 3
f.eof? # => true
f.close
Iterating over lines in a stream usually changes its line number:
File.open('t.txt') do |f|
f.each_line do |line|
p "position=#{f.pos} eof?=#{f.eof?} lineno=#{f.lineno}"
end
end
Output:
"position=11 eof?=false lineno=1"
"position=23 eof?=false lineno=2"
"position=24 eof?=false lineno=3"
"position=36 eof?=false lineno=4"
"position=47 eof?=true lineno=5"
==== Line Options
A number of \IO methods accept optional keyword arguments
that determine how lines in a stream are to be treated:
- +:chomp+: If +true+, line separators are omitted; default is +false+.
=== Character \IO
You can process an \IO stream character-by-character using these methods:
- IO#getc: Reads and returns the next character from the stream:
f = File.new('t.rus')
f.getc # => "т"
f.getc # => "е"
f.getc # => "с"
f.getc # => "т"
f.getc # => nil
- IO#readchar (not in \StringIO):
Like #getc, but raises an exception at end-of-stream:
f.readchar # Raises EOFError.
- IO#ungetc (not in \ARGF):
Pushes back ("unshifts") a character or integer onto the stream:
path = 't.tmp'
File.write(path, 'foo')
File.open(path) do |f|
f.ungetc('т')
f.read # => "тfoo"
end
- IO#putc (also in Kernel): Writes a character to the stream:
File.open('t.tmp', 'w') do |f|
f.putc('т')
f.putc('е')
f.putc('с')
f.putc('т')
end
File.read('t.tmp') # => "тест"
- IO#each_char: Reads each remaining character in the stream,
passing the character to the given block:
File.open('t.rus') do |f|
f.pos = 4
f.each_char {|c| p c }
end
Output:
"с"
"т"
=== Byte \IO
You can process an \IO stream byte-by-byte using these methods:
- IO#getbyte: Returns the next 8-bit byte as an integer in range 0..255:
File.read('t.dat')
# => "\xFE\xFF\x99\x90\x99\x91\x99\x92\x99\x93\x99\x94"
File.read('t.dat')
# => "\xFE\xFF\x99\x90\x99\x91\x99\x92\x99\x93\x99\x94"
f = File.new('t.dat')
f.getbyte # => 254
f.getbyte # => 255
f.seek(-2, :END)
f.getbyte # => 153
f.getbyte # => 148
f.getbyte # => nil
- IO#readbyte (not in \StringIO):
Like #getbyte, but raises an exception if at end-of-stream:
f.readbyte # Raises EOFError.
- IO#ungetbyte (not in \ARGF):
Pushes back ("unshifts") a byte back onto the stream:
f.ungetbyte(0)
f.ungetbyte(01)
f.read # => "\u0001\u0000"
- IO#each_byte: Reads each remaining byte in the stream,
passing the byte to the given block:
f.seek(-4, :END)
f.each_byte {|b| p b }
Output:
153
147
153
148
=== Codepoint \IO
You can process an \IO stream codepoint-by-codepoint using method
+#each_codepoint+:
a = []
File.open('t.rus') do |f|
f.each_codepoint {|c| a << c }
end
a # => [1090, 1077, 1089, 1090]

2
file.c
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@ -7147,7 +7147,7 @@ const char ruby_null_device[] =
* strings read are converted from external to internal encoding,
* and strings written are converted from internal to external encoding.
* For further details about transcoding input and output,
* see {Encodings}[rdoc-ref:io_streams.rdoc@Encodings].
* see {Encodings}[rdoc-ref:encodings.rdoc@Encodings].
*
* If the external encoding is <tt>'BOM|UTF-8'</tt>, <tt>'BOM|UTF-16LE'</tt>
* or <tt>'BOM|UTF16-BE'</tt>,

548
io.c
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@ -2373,7 +2373,7 @@ rb_io_flush(VALUE io)
* tell -> integer
*
* Returns the current position (in bytes) in +self+
* (see {Position}[rdoc-ref:io_streams.rdoc@Position]):
* (see {Position}[rdoc-ref:IO@Position]):
*
* f = File.open('t.txt')
* f.tell # => 0
@ -2439,7 +2439,7 @@ interpret_seek_whence(VALUE vwhence)
* seek(offset, whence = IO::SEEK_SET) -> 0
*
* Seeks to the position given by integer +offset+
* (see {Position}[rdoc-ref:io_streams.rdoc@Position])
* (see {Position}[rdoc-ref:IO@Position])
* and constant +whence+, which is one of:
*
* - +:CUR+ or <tt>IO::SEEK_CUR</tt>:
@ -2499,7 +2499,7 @@ rb_io_seek_m(int argc, VALUE *argv, VALUE io)
* pos = new_position -> new_position
*
* Seeks to the given +new_position+ (in bytes);
* see {Position}[rdoc-ref:io_streams.rdoc@Position]:
* see {Position}[rdoc-ref:IO@Position]:
*
* f = File.open('t.txt')
* f.tell # => 0
@ -2533,8 +2533,8 @@ static void clear_readconv(rb_io_t *fptr);
*
* Repositions the stream to its beginning,
* setting both the position and the line number to zero;
* see {Position}[rdoc-ref:io_streams.rdoc@Position]
* and {Line Number}[rdoc-ref:io_streams.rdoc@Line+Number]:
* see {Position}[rdoc-ref:IO@Position]
* and {Line Number}[rdoc-ref:IO@Line+Number]:
*
* f = File.open('t.txt')
* f.tell # => 0
@ -2624,7 +2624,7 @@ io_fillbuf(rb_io_t *fptr)
* eof -> true or false
*
* Returns +true+ if the stream is positioned at its end, +false+ otherwise;
* see {Position}[rdoc-ref:io_streams.rdoc@Position]:
* see {Position}[rdoc-ref:IO@Position]:
*
* f = File.open('t.txt')
* f.eof # => false
@ -3640,10 +3640,11 @@ io_write_nonblock(rb_execution_context_t *ec, VALUE io, VALUE str, VALUE ex)
/*
* call-seq:
* read(maxlen = nil) -> string or nil
* read(maxlen = nil, out_string) -> out_string or nil
* read(maxlen = nil, out_string = nil) -> new_string, out_string, or nil
*
* Reads bytes from the stream (in binary mode):
* Reads bytes from the stream, (in binary mode);
* the stream must be opened for reading
* (see {Access Modes}[rdoc-ref:File@Access+Modes]):
*
* - If +maxlen+ is +nil+, reads all bytes.
* - Otherwise reads +maxlen+ bytes, if available.
@ -4192,13 +4193,13 @@ rb_io_gets_internal(VALUE io)
/*
* call-seq:
* gets(sep = $/, **line_opts) -> string or nil
* gets(limit, **line_opts) -> string or nil
* gets(sep, limit, **line_opts) -> string or nil
* gets(sep = $/, chomp: false) -> string or nil
* gets(limit, chomp: false) -> string or nil
* gets(sep, limit, chomp: false) -> string or nil
*
* Reads and returns a line from the stream;
* assigns the return value to <tt>$_</tt>.
* See {Line IO}[rdoc-ref:io_streams.rdoc@Line+IO].
* See {Line IO}[rdoc-ref:IO@Line+IO].
*
* With no arguments given, returns the next line
* as determined by line separator <tt>$/</tt>, or +nil+ if none:
@ -4215,7 +4216,7 @@ rb_io_gets_internal(VALUE io)
* With only string argument +sep+ given,
* returns the next line as determined by line separator +sep+,
* or +nil+ if none;
* see {Line Separator}[rdoc-ref:io_streams.rdoc@Line+Separator]:
* see {Line Separator}[rdoc-ref:IO@Line+Separator]:
*
* f = File.new('t.txt')
* f.gets('l') # => "First l"
@ -4236,7 +4237,7 @@ rb_io_gets_internal(VALUE io)
*
* With only integer argument +limit+ given,
* limits the number of bytes in the line;
* see {Line Limit}[rdoc-ref:io_streams.rdoc@Line+Limit]:
* see {Line Limit}[rdoc-ref:IO@Line+Limit]:
*
* # No more than one line.
* File.open('t.txt') {|f| f.gets(10) } # => "First line"
@ -4250,8 +4251,8 @@ rb_io_gets_internal(VALUE io)
* or +nil+ if none.
* - But returns no more bytes than are allowed by the limit.
*
* For all forms above, optional keyword arguments +line_opts+ specify
* {Line Options}[rdoc-ref:io_streams.rdoc@Line+Options]:
* Optional keyword argument +chomp+ specifies whether line separators
* are to be omitted:
*
* f = File.open('t.txt')
* # Chomp the lines.
@ -4280,8 +4281,8 @@ rb_io_gets_m(int argc, VALUE *argv, VALUE io)
* call-seq:
* lineno -> integer
*
* Returns the current line number for the stream.
* See {Line Number}[rdoc-ref:io_streams.rdoc@Line+Number].
* Returns the current line number for the stream;
* see {Line Number}[rdoc-ref:IO@Line+Number].
*
*/
@ -4299,8 +4300,8 @@ rb_io_lineno(VALUE io)
* call-seq:
* lineno = integer -> integer
*
* Sets and returns the line number for the stream.
* See {Line Number}[rdoc-ref:io_streams.rdoc@Line+Number].
* Sets and returns the line number for the stream;
* see {Line Number}[rdoc-ref:IO@Line+Number].
*
*/
@ -4317,12 +4318,14 @@ rb_io_set_lineno(VALUE io, VALUE lineno)
/*
* call-seq:
* readline(sep = $/, **line_opts) -> string
* readline(limit, **line_opts) -> string
* readline(sep, limit, **line_opts) -> string
* readline(sep = $/, chomp: false) -> string
* readline(limit, chomp: false) -> string
* readline(sep, limit, chomp: false) -> string
*
* Reads a line as with IO#gets, but raises EOFError if already at end-of-file.
* Reads a line as with IO#gets, but raises EOFError if already at end-of-stream.
*
* Optional keyword argument +chomp+ specifies whether line separators
* are to be omitted.
*/
static VALUE
@ -4340,13 +4343,13 @@ static VALUE io_readlines(const struct getline_arg *arg, VALUE io);
/*
* call-seq:
* readlines(sep = $/, **line_opts) -> array
* readlines(limit, **line_opts) -> array
* readlines(sep, limit, **line_opts) -> array
* readlines(sep = $/, chomp: false) -> array
* readlines(limit, chomp: false) -> array
* readlines(sep, limit, chomp: false) -> array
*
* Reads and returns all remaining line from the stream;
* does not modify <tt>$_</tt>.
* See {Line IO}[rdoc-ref:io_streams.rdoc@Line+IO].
* See {Line IO}[rdoc-ref:IO@Line+IO].
*
* With no arguments given, returns lines
* as determined by line separator <tt>$/</tt>, or +nil+ if none:
@ -4360,7 +4363,7 @@ static VALUE io_readlines(const struct getline_arg *arg, VALUE io);
* With only string argument +sep+ given,
* returns lines as determined by line separator +sep+,
* or +nil+ if none;
* see {Line Separator}[rdoc-ref:io_streams.rdoc@Line+Separator]:
* see {Line Separator}[rdoc-ref:IO@Line+Separator]:
*
* f = File.new('t.txt')
* f.readlines('li')
@ -4381,7 +4384,7 @@ static VALUE io_readlines(const struct getline_arg *arg, VALUE io);
*
* With only integer argument +limit+ given,
* limits the number of bytes in each line;
* see {Line Limit}[rdoc-ref:io_streams.rdoc@Line+Limit]:
* see {Line Limit}[rdoc-ref:IO@Line+Limit]:
*
* f = File.new('t.txt')
* f.readlines(8)
@ -4394,8 +4397,8 @@ static VALUE io_readlines(const struct getline_arg *arg, VALUE io);
* - Returns lines as determined by line separator +sep+.
* - But returns no more bytes in a line than are allowed by the limit.
*
* For all forms above, optional keyword arguments +line_opts+ specify
* {Line Options}[rdoc-ref:io_streams.rdoc@Line+Options]:
* Optional keyword argument +chomp+ specifies whether line separators
* are to be omitted:
*
* f = File.new('t.txt')
* f.readlines(chomp: true)
@ -4429,15 +4432,15 @@ io_readlines(const struct getline_arg *arg, VALUE io)
/*
* call-seq:
* each_line(sep = $/, **line_opts) {|line| ... } -> self
* each_line(limit, **line_opts) {|line| ... } -> self
* each_line(sep, limit, **line_opts) {|line| ... } -> self
* each_line(sep = $/, chomp: false) {|line| ... } -> self
* each_line(limit, chomp: false) {|line| ... } -> self
* each_line(sep, limit, chomp: false) {|line| ... } -> self
* each_line -> enumerator
*
* Calls the block with each remaining line read from the stream;
* does nothing if already at end-of-file;
* returns +self+.
* See {Line IO}[rdoc-ref:io_streams.rdoc@Line+IO].
* Does nothing if already at end-of-stream;
* See {Line IO}[rdoc-ref:IO@Line+IO].
*
* With no arguments given, reads lines
* as determined by line separator <tt>$/</tt>:
@ -4457,7 +4460,7 @@ io_readlines(const struct getline_arg *arg, VALUE io)
*
* With only string argument +sep+ given,
* reads lines as determined by line separator +sep+;
* see {Line Separator}[rdoc-ref:io_streams.rdoc@Line+Separator]:
* see {Line Separator}[rdoc-ref:IO@Line+Separator]:
*
* f = File.new('t.txt')
* f.each_line('li') {|line| p line }
@ -4493,7 +4496,7 @@ io_readlines(const struct getline_arg *arg, VALUE io)
*
* With only integer argument +limit+ given,
* limits the number of bytes in each line;
* see {Line Limit}[rdoc-ref:io_streams.rdoc@Line+Limit]:
* see {Line Limit}[rdoc-ref:IO@Line+Limit]:
*
* f = File.new('t.txt')
* f.each_line(8) {|line| p line }
@ -4517,8 +4520,8 @@ io_readlines(const struct getline_arg *arg, VALUE io)
* - Calls with the next line as determined by line separator +sep+.
* - But returns no more bytes than are allowed by the limit.
*
* For all forms above, optional keyword arguments +line_opts+ specify
* {Line Options}[rdoc-ref:io_streams.rdoc@Line+Options]:
* Optional keyword argument +chomp+ specifies whether line separators
* are to be omitted:
*
* f = File.new('t.txt')
* f.each_line(chomp: true) {|line| p line }
@ -4560,7 +4563,7 @@ rb_io_each_line(int argc, VALUE *argv, VALUE io)
* each_byte -> enumerator
*
* Calls the given block with each byte (0..255) in the stream; returns +self+.
* See {Byte IO}[rdoc-ref:io_streams.rdoc@Byte+IO].
* See {Byte IO}[rdoc-ref:IO@Byte+IO].
*
* f = File.new('t.rus')
* a = []
@ -4708,7 +4711,7 @@ io_getc(rb_io_t *fptr, rb_encoding *enc)
* each_char -> enumerator
*
* Calls the given block with each character in the stream; returns +self+.
* See {Character IO}[rdoc-ref:io_streams.rdoc@Character+IO].
* See {Character IO}[rdoc-ref:IO@Character+IO].
*
* f = File.new('t.rus')
* a = []
@ -4869,8 +4872,8 @@ rb_io_each_codepoint(VALUE io)
* getc -> character or nil
*
* Reads and returns the next 1-character string from the stream;
* returns +nil+ if already at end-of-file.
* See {Character IO}[rdoc-ref:io_streams.rdoc@Character+IO].
* returns +nil+ if already at end-of-stream.
* See {Character IO}[rdoc-ref:IO@Character+IO].
*
* f = File.open('t.txt')
* f.getc # => "F"
@ -4902,8 +4905,8 @@ rb_io_getc(VALUE io)
* readchar -> string
*
* Reads and returns the next 1-character string from the stream;
* raises EOFError if already at end-of-file.
* See {Character IO}[rdoc-ref:io_streams.rdoc@Character+IO].
* raises EOFError if already at end-of-stream.
* See {Character IO}[rdoc-ref:IO@Character+IO].
*
* f = File.open('t.txt')
* f.readchar # => "F"
@ -4932,8 +4935,8 @@ rb_io_readchar(VALUE io)
* getbyte -> integer or nil
*
* Reads and returns the next byte (in range 0..255) from the stream;
* returns +nil+ if already at end-of-file.
* See {Byte IO}[rdoc-ref:io_streams.rdoc@Byte+IO].
* returns +nil+ if already at end-of-stream.
* See {Byte IO}[rdoc-ref:IO@Byte+IO].
*
* f = File.open('t.txt')
* f.getbyte # => 70
@ -4943,7 +4946,6 @@ rb_io_readchar(VALUE io)
* f.close
*
* Related: IO#readbyte (may raise EOFError).
*
*/
VALUE
@ -4977,8 +4979,8 @@ rb_io_getbyte(VALUE io)
* readbyte -> integer
*
* Reads and returns the next byte (in range 0..255) from the stream;
* raises EOFError if already at end-of-file.
* See {Byte IO}[rdoc-ref:io_streams.rdoc@Byte+IO].
* raises EOFError if already at end-of-stream.
* See {Byte IO}[rdoc-ref:IO@Byte+IO].
*
* f = File.open('t.txt')
* f.readbyte # => 70
@ -5009,7 +5011,7 @@ rb_io_readbyte(VALUE io)
*
* Pushes back ("unshifts") the given data onto the stream's buffer,
* placing the data so that it is next to be read; returns +nil+.
* See {Byte IO}[rdoc-ref:io_streams.rdoc@Byte+IO].
* See {Byte IO}[rdoc-ref:IO@Byte+IO].
*
* Note that:
*
@ -5070,7 +5072,7 @@ rb_io_ungetbyte(VALUE io, VALUE b)
*
* Pushes back ("unshifts") the given data onto the stream's buffer,
* placing the data so that it is next to be read; returns +nil+.
* See {Character IO}[rdoc-ref:io_streams.rdoc@Character+IO].
* See {Character IO}[rdoc-ref:IO@Character+IO].
*
* Note that:
*
@ -5155,8 +5157,10 @@ rb_io_ungetc(VALUE io, VALUE c)
* Returns +true+ if the stream is associated with a terminal device (tty),
* +false+ otherwise:
*
* File.new('t.txt').isatty #=> false
* File.new('/dev/tty').isatty #=> true
* f = File.new('t.txt').isatty #=> false
* f.close
* f = File.new('/dev/tty').isatty #=> true
* f.close
*
* IO#tty? is an alias for IO#isatty.
*
@ -5639,6 +5643,7 @@ rb_io_close(VALUE io)
*
* Closes the stream for both reading and writing
* if open for either or both; returns +nil+.
* See {Open and Closed Streams}[rdoc-ref:IO@Open+and+Closed+Streams].
*
* If the stream is open for writing, flushes any buffered writes
* to the operating system before closing.
@ -5710,7 +5715,8 @@ io_close(VALUE io)
* closed? -> true or false
*
* Returns +true+ if the stream is closed for both reading and writing,
* +false+ otherwise:
* +false+ otherwise.
* See {Open and Closed Streams}[rdoc-ref:IO@Open+and+Closed+Streams].
*
* IO.popen('ruby', 'r+') do |pipe|
* puts pipe.closed?
@ -5726,8 +5732,6 @@ io_close(VALUE io)
* false
* true
*
* See also {Open and Closed Streams}[rdoc-ref:io_streams.rdoc@Open+and+Closed+Streams].
*
* Related: IO#close_read, IO#close_write, IO#close.
*/
@ -5757,6 +5761,7 @@ rb_io_closed(VALUE io)
*
* Closes the stream for reading if open for reading;
* returns +nil+.
* See {Open and Closed Streams}[rdoc-ref:IO@Open+and+Closed+Streams].
*
* If the stream was opened by IO.popen and is also closed for writing,
* sets global variable <tt>$?</tt> (child exit status).
@ -5779,8 +5784,6 @@ rb_io_closed(VALUE io)
* pid 14748 exit 0
* true
*
* See also {Open and Closed Streams}[rdoc-ref:io_streams.rdoc@Open+and+Closed+Streams].
*
* Related: IO#close, IO#close_write, IO#closed?.
*/
@ -5830,7 +5833,8 @@ rb_io_close_read(VALUE io)
* close_write -> nil
*
* Closes the stream for writing if open for writing;
* returns +nil+:
* returns +nil+.
* See {Open and Closed Streams}[rdoc-ref:IO@Open+and+Closed+Streams].
*
* Flushes any buffered writes to the operating system before closing.
*
@ -5853,8 +5857,6 @@ rb_io_close_read(VALUE io)
* pid 15044 exit 0
* true
*
* See also {Open and Closed Streams}[rdoc-ref:io_streams.rdoc@Open+and+Closed+Streams].
*
* Related: IO#close, IO#close_read, IO#closed?.
*/
@ -6066,7 +6068,7 @@ pread_internal_call(VALUE arg)
*
* - Reads at the given +offset+ (in bytes).
* - Disregards, and does not modify, the stream's position
* (see {Position}[rdoc-ref:io_streams.rdoc@Position]).
* (see {Position}[rdoc-ref:IO@Position]).
* - Bypasses any user space buffering in the stream.
*
* Because this method does not disturb the stream's state
@ -6142,7 +6144,7 @@ internal_pwrite_func(void *ptr)
*
* - Writes at the given +offset+ (in bytes).
* - Disregards, and does not modify, the stream's position
* (see {Position}[rdoc-ref:io_streams.rdoc@Position]).
* (see {Position}[rdoc-ref:IO@Position]).
* - Bypasses any user space buffering in the stream.
*
* Because this method does not disturb the stream's state
@ -8577,7 +8579,7 @@ deprecated_str_setter(VALUE val, ID id, VALUE *var)
* Writes the given objects to the stream; returns +nil+.
* Appends the output record separator <tt>$OUTPUT_RECORD_SEPARATOR</tt>
* (<tt>$\\</tt>), if it is not +nil+.
* See {Line IO}[rdoc-ref:io_streams.rdoc@Line+IO].
* See {Line IO}[rdoc-ref:IO@Line+IO].
*
* With argument +objects+ given, for each object:
*
@ -8715,7 +8717,7 @@ rb_f_print(int argc, const VALUE *argv, VALUE _)
* putc(object) -> object
*
* Writes a character to the stream.
* See {Character IO}[rdoc-ref:io_streams.rdoc@Character+IO].
* See {Character IO}[rdoc-ref:IO@Character+IO].
*
* If +object+ is numeric, converts to integer if necessary,
* then writes the character whose code is the
@ -8819,7 +8821,7 @@ io_puts_ary(VALUE ary, VALUE out, int recur)
* returns +nil+.\
* Writes a newline after each that does not already end with a newline sequence.
* If called without arguments, writes a newline.
* See {Line IO}[rdoc-ref:io_streams.rdoc@Line+IO].
* See {Line IO}[rdoc-ref:IO@Line+IO].
*
* Note that each added newline is the character <tt>"\n"<//tt>,
* not the output record separator (<tt>$\\</tt>).
@ -9424,31 +9426,32 @@ rb_io_set_encoding_by_bom(VALUE io)
*
* Argument +path+ must be a valid file path:
*
* File.new('/etc/fstab')
* File.new('t.txt')
* f = File.new('/etc/fstab')
* f.close
* f = File.new('t.txt')
* f.close
*
* Optional argument +mode+ (defaults to 'r') must specify a valid mode;
* see {Access Modes}[rdoc-ref:File@Access+Modes]:
*
* File.new('t.tmp', 'w')
* File.new('t.tmp', File::RDONLY)
* f = File.new('t.tmp', 'w')
* f.close
* f = File.new('t.tmp', File::RDONLY)
* f.close
*
* Optional argument +perm+ (defaults to 0666) must specify valid permissions
* see {File Permissions}[rdoc-ref:File@File+Permissions]:
*
* File.new('t.tmp', File::CREAT, 0644)
* File.new('t.tmp', File::CREAT, 0444)
* f = File.new('t.tmp', File::CREAT, 0644)
* f.close
* f = File.new('t.tmp', File::CREAT, 0444)
* f.close
*
* Optional keyword arguments +opts+ specify:
*
* - {Open Options}[rdoc-ref:IO@Open+Options].
* - {Encoding options}[rdoc-ref:encodings.rdoc@Encoding+Options].
*
* Examples:
*
* File.new('t.tmp', autoclose: true)
* File.new('t.tmp', internal_encoding: nil)
*
*/
static VALUE
@ -10231,9 +10234,9 @@ static VALUE argf_readline(int, VALUE *, VALUE);
/*
* call-seq:
* readline(sep = $/, **line_opts) -> string
* readline(limit, **line_opts) -> string
* readline(sep, limit, **line_opts) -> string
* readline(sep = $/, chomp: false) -> string
* readline(limit, chomp: false) -> string
* readline(sep, limit, chomp: false) -> string
*
* Equivalent to method Kernel#gets, except that it raises an exception
* if called at end-of-stream:
@ -10242,6 +10245,8 @@ static VALUE argf_readline(int, VALUE *, VALUE);
* ["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"]
* in `readline': end of file reached (EOFError)
*
* Optional keyword argument +chomp+ specifies whether line separators
* are to be omitted.
*/
static VALUE
@ -10290,18 +10295,18 @@ static VALUE argf_readlines(int, VALUE *, VALUE);
/*
* call-seq:
* readlines(sep = $/, **line_opts) -> array
* readlines(limit, **line_opts) -> array
* readlines(sep, limit, **line_opts) -> array
* readlines(sep = $/, chomp: false, **enc_opts) -> array
* readlines(limit, chomp: false, **enc_opts) -> array
* readlines(sep, limit, chomp: false, **enc_opts) -> array
*
* Returns an array containing the lines returned by calling
* Kernel#gets until the end-of-file is reached;
* (see {Line IO}[rdoc-ref:io_streams.rdoc@Line+IO]).
* Kernel#gets until the end-of-stream is reached;
* (see {Line IO}[rdoc-ref:IO@Line+IO]).
*
* With only string argument +sep+ given,
* returns the remaining lines as determined by line separator +sep+,
* or +nil+ if none;
* see {Line Separator}[rdoc-ref:io_streams.rdoc@Line+Separator]:
* see {Line Separator}[rdoc-ref:IO@Line+Separator]:
*
* # Default separator.
* $ cat t.txt | ruby -e "p readlines"
@ -10321,7 +10326,7 @@ static VALUE argf_readlines(int, VALUE *, VALUE);
*
* With only integer argument +limit+ given,
* limits the number of bytes in the line;
* see {Line Limit}[rdoc-ref:io_streams.rdoc@Line+Limit]:
* see {Line Limit}[rdoc-ref:IO@Line+Limit]:
*
* $cat t.txt | ruby -e "p readlines 10"
* ["First line", "\n", "Second lin", "e\n", "\n", "Fourth lin", "e\n", "Fifth line", "\n"]
@ -10333,18 +10338,17 @@ static VALUE argf_readlines(int, VALUE *, VALUE);
* ["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"]
*
* With arguments +sep+ and +limit+ given, combines the two behaviors;
* see {Line Separator and Line Limit}[rdoc-ref:io_streams.rdoc@Line+Separator+and+Line+Limit].
* see {Line Separator and Line Limit}[rdoc-ref:IO@Line+Separator+and+Line+Limit].
*
* For all forms above, optional keyword arguments specify:
*
* - {Line Options}[rdoc-ref:io_streams.rdoc@Line+Options].
* - {Encoding options}[rdoc-ref:encodings.rdoc@Encoding+Options].
*
* Examples:
* Optional keyword argument +chomp+ specifies whether line separators
* are to be omitted:
*
* $ cat t.txt | ruby -e "p readlines(chomp: true)"
* ["First line", "Second line", "", "Fourth line", "Fifth line"]
*
* Optional keyword arguments +enc_opts+ specify encoding options;
* see {Encoding options}[rdoc-ref:encodings.rdoc@Encoding+Options].
*
*/
static VALUE
@ -11828,7 +11832,7 @@ io_s_foreach(VALUE v)
* For both forms, command and path, the remaining arguments are the same.
*
* With argument +sep+ given, parses lines as determined by that line separator
* (see {Line Separator}[rdoc-ref:io_streams.rdoc@Line+Separator]):
* (see {Line Separator}[rdoc-ref:IO@Line+Separator]):
*
* File.foreach('t.txt', 'li') {|line| p line }
*
@ -11851,7 +11855,7 @@ io_s_foreach(VALUE v)
*
* With argument +limit+ given, parses lines as determined by the default
* line separator and the given line-length limit
* (see {Line Limit}[rdoc-ref:io_streams.rdoc@Line+Limit]):
* (see {Line Limit}[rdoc-ref:IO@Line+Limit]):
*
* File.foreach('t.txt', 7) {|line| p line }
*
@ -11870,13 +11874,13 @@ io_s_foreach(VALUE v)
* With arguments +sep+ and +limit+ given,
* parses lines as determined by the given
* line separator and the given line-length limit
* (see {Line Separator and Line Limit}[rdoc-ref:io_streams.rdoc@Line+Separator+and+Line+Limit]):
* (see {Line Separator and Line Limit}[rdoc-ref:IO@Line+Separator+and+Line+Limit]):
*
* Optional keyword arguments +opts+ specify:
*
* - {Open Options}[rdoc-ref:IO@Open+Options].
* - {Encoding options}[rdoc-ref:encodings.rdoc@Encoding+Options].
* - {Line Options}[rdoc-ref:io_streams.rdoc@Line+Options].
* - {Line Options}[rdoc-ref:IO@Line+Options].
*
* Returns an Enumerator if no block is given.
*
@ -11946,7 +11950,7 @@ io_s_readlines(VALUE v)
* For both forms, command and path, the remaining arguments are the same.
*
* With argument +sep+ given, parses lines as determined by that line separator
* (see {Line Separator}[rdoc-ref:io_streams.rdoc@Line+Separator]):
* (see {Line Separator}[rdoc-ref:IO@Line+Separator]):
*
* # Ordinary separator.
* IO.readlines('t.txt', 'li')
@ -11960,7 +11964,7 @@ io_s_readlines(VALUE v)
*
* With argument +limit+ given, parses lines as determined by the default
* line separator and the given line-length limit
* (see {Line Limit}[rdoc-ref:io_streams.rdoc@Line+Limit]):
* (see {Line Limit}[rdoc-ref:IO@Line+Limit]):
*
* IO.readlines('t.txt', 7)
* # => ["First l", "ine\n", "Second ", "line\n", "\n", "Third l", "ine\n", "Fourth ", "line\n"]
@ -11968,13 +11972,13 @@ io_s_readlines(VALUE v)
* With arguments +sep+ and +limit+ given,
* parses lines as determined by the given
* line separator and the given line-length limit
* (see {Line Separator and Line Limit}[rdoc-ref:io_streams.rdoc@Line+Separator+and+Line+Limit]):
* (see {Line Separator and Line Limit}[rdoc-ref:IO@Line+Separator+and+Line+Limit]):
*
* Optional keyword arguments +opts+ specify:
*
* - {Open Options}[rdoc-ref:IO@Open+Options].
* - {Encoding options}[rdoc-ref:encodings.rdoc@Encoding+Options].
* - {Line Options}[rdoc-ref:io_streams.rdoc@Line+Options].
* - {Line Options}[rdoc-ref:IO@Line+Options].
*
*/
@ -14687,10 +14691,10 @@ set_LAST_READ_LINE(VALUE val, ID _x, VALUE *_y)
*
* - A position, which determines where in the stream the next
* read or write is to occur;
* see {Position}[rdoc-ref:io_streams.rdoc@Position].
* see {Position}[rdoc-ref:IO@Position].
* - A line number, which is a special, line-oriented, "position"
* (different from the position mentioned above);
* see {Line Number}[rdoc-ref:io_streams.rdoc@Line+Number].
* see {Line Number}[rdoc-ref:IO@Line+Number].
*
* == Extension <tt>io/console</tt>
*
@ -14725,6 +14729,326 @@ set_LAST_READ_LINE(VALUE val, ID _x, VALUE *_y)
* Also available are the options offered in String#encode,
* which may control conversion between external internal encoding.
*
* == Basic \IO
*
* You can perform basic stream \IO with these methods,
* which typically operate on multi-byte strings:
*
* - IO#read: Reads and returns some or all of the remaining bytes from the stream.
* - IO#write: Writes zero or more strings to the stream;
* each given object that is not already a string is converted via +to_s+.
*
* === Position
*
* An \IO stream has a nonnegative integer _position_,
* which is the byte offset at which the next read or write is to occur.
* A new stream has position zero (and line number zero);
* method +rewind+ resets the position (and line number) to zero.
*
* The relevant methods:
*
* - IO#tell (aliased as +#pos+): Returns the current position (in bytes) in the stream.
* - IO#pos=: Sets the position of the stream to a given integer +new_position+ (in bytes).
* - IO#seek: Sets the position of the stream to a given integer +offset+ (in bytes),
* relative to a given position +whence+
* (indicating the beginning, end, or current position).
* - IO#rewind: Positions the stream at the beginning (also resetting the line number).
*
* === Open and Closed Streams
*
* A new \IO stream may be open for reading, open for writing, or both.
*
* A stream is automatically closed when claimed by the garbage collector.
*
* Attempted reading or writing on a closed stream raises an exception.
*
* The relevant methods:
*
* - IO#close: Closes the stream for both reading and writing.
* - IO#close_read: Closes the stream for reading.
* - IO#close_write: Closes the stream for writing.
* - IO#closed?: Returns whether the stream is closed.
*
* === End-of-Stream
*
* You can query whether a stream is positioned at its end:
*
* - IO#eof? (also aliased as +#eof+): Returns whether the stream is at end-of-stream.
*
* You can reposition to end-of-stream by using method IO#seek:
*
* f = File.new('t.txt')
* f.eof? # => false
* f.seek(0, :END)
* f.eof? # => true
* f.close
*
* Or by reading all stream content (which is slower than using IO#seek):
*
* f.rewind
* f.eof? # => false
* f.read # => "First line\nSecond line\n\nFourth line\nFifth line\n"
* f.eof? # => true
*
* == Line \IO
*
* You can read an \IO stream line-by-line using these methods:
*
* - IO#each_line: Reads each remaining line, passing it to the given block.
* - IO#gets: Returns the next line.
* - IO#readline: Like #gets, but raises an exception at end-of-stream.
* - IO#readlines: Returns all remaining lines in an array.
*
* Each of these reader methods accepts:
*
* - An optional line separator, +sep+;
* see {Line Separator}[rdoc-ref:IO@Line+Separator].
* - An optional line-size limit, +limit+;
* see {Line Limit}[rdoc-ref:IO@Line+Limit].
*
* For each of these reader methods, reading may begin mid-line,
* depending on the stream's position;
* see {Position}[rdoc-ref:IO@Position]:
*
* f = File.new('t.txt')
* f.pos = 27
* f.each_line {|line| p line }
* f.close
*
* Output:
*
* "rth line\n"
* "Fifth line\n"
*
* You can write to an \IO stream line-by-line using this method:
*
* - IO#puts: Writes objects to the stream.
*
* === Line Separator
*
* Each of these methods uses a <i>line separator</i>,
* which is the string that delimits lines:
*
* - IO.foreach.
* - IO.readlines.
* - IO#each_line.
* - IO#gets.
* - IO#readline.
* - IO#readlines.
*
* The default line separator is the given by the global variable <tt>$/</tt>,
* whose value is by default <tt>"\n"</tt>.
* The line to be read next is all data from the current position
* to the next line separator:
*
* f = File.new('t.txt')
* f.gets # => "First line\n"
* f.gets # => "Second line\n"
* f.gets # => "\n"
* f.gets # => "Fourth line\n"
* f.gets # => "Fifth line\n"
* f.close
*
* You can specify a different line separator:
*
* f = File.new('t.txt')
* f.gets('l') # => "First l"
* f.gets('li') # => "ine\nSecond li"
* f.gets('lin') # => "ne\n\nFourth lin"
* f.gets # => "e\n"
* f.close
*
* There are two special line separators:
*
* - +nil+: The entire stream is read into a single string:
*
* f = File.new('t.txt')
* f.gets(nil) # => "First line\nSecond line\n\nFourth line\nFifth line\n"
* f.close
*
* - <tt>''</tt> (the empty string): The next "paragraph" is read
* (paragraphs being separated by two consecutive line separators):
*
* f = File.new('t.txt')
* f.gets('') # => "First line\nSecond line\n\n"
* f.gets('') # => "Fourth line\nFifth line\n"
* f.close
*
* === Line Limit
*
* Each of these methods uses a <i>line limit</i>,
* which specifies that the number of bytes returned may not be (much) longer
* than the given +limit+;
*
* - IO.foreach.
* - IO.readlines.
* - IO#each_line.
* - IO#gets.
* - IO#readline.
* - IO#readlines.
*
* A multi-byte character will not be split, and so a line may be slightly longer
* than the given limit.
*
* If +limit+ is not given, the line is determined only by +sep+.
*
* # Text with 1-byte characters.
* File.open('t.txt') {|f| f.gets(1) } # => "F"
* File.open('t.txt') {|f| f.gets(2) } # => "Fi"
* File.open('t.txt') {|f| f.gets(3) } # => "Fir"
* File.open('t.txt') {|f| f.gets(4) } # => "Firs"
* # No more than one line.
* File.open('t.txt') {|f| f.gets(10) } # => "First line"
* File.open('t.txt') {|f| f.gets(11) } # => "First line\n"
* File.open('t.txt') {|f| f.gets(12) } # => "First line\n"
*
* # Text with 2-byte characters, which will not be split.
* File.open('t.rus') {|f| f.gets(1).size } # => 1
* File.open('t.rus') {|f| f.gets(2).size } # => 1
* File.open('t.rus') {|f| f.gets(3).size } # => 2
* File.open('t.rus') {|f| f.gets(4).size } # => 2
*
* === Line Separator and Line Limit
*
* With arguments +sep+ and +limit+ given,
* combines the two behaviors:
*
* - Returns the next line as determined by line separator +sep+.
* - But returns no more bytes than are allowed by the limit.
*
* Example:
*
* File.open('t.txt') {|f| f.gets('li', 20) } # => "First li"
* File.open('t.txt') {|f| f.gets('li', 2) } # => "Fi"
*
* === Line Number
*
* A readable \IO stream has a non-negative integer <i>line number</i>.
*
* The relevant methods:
*
* - IO#lineno: Returns the line number.
* - IO#lineno=: Resets and returns the line number.
*
* Unless modified by a call to method IO#lineno=,
* the line number is the number of lines read
* by certain line-oriented methods,
* according to the given line separator +sep+:
*
* - IO.foreach: Increments the line number on each call to the block.
* - IO#each_line: Increments the line number on each call to the block.
* - IO#gets: Increments the line number.
* - IO#readline: Increments the line number.
* - IO#readlines: Increments the line number for each line read.
*
* A new stream is initially has line number zero (and position zero);
* method +rewind+ resets the line number (and position) to zero:
*
* f = File.new('t.txt')
* f.lineno # => 0
* f.gets # => "First line\n"
* f.lineno # => 1
* f.rewind
* f.lineno # => 0
* f.close
*
* Reading lines from a stream usually changes its line number:
*
* f = File.new('t.txt', 'r')
* f.lineno # => 0
* f.readline # => "This is line one.\n"
* f.lineno # => 1
* f.readline # => "This is the second line.\n"
* f.lineno # => 2
* f.readline # => "Here's the third line.\n"
* f.lineno # => 3
* f.eof? # => true
* f.close
*
* Iterating over lines in a stream usually changes its line number:
*
* File.open('t.txt') do |f|
* f.each_line do |line|
* p "position=#{f.pos} eof?=#{f.eof?} lineno=#{f.lineno}"
* end
* end
*
* Output:
*
* "position=11 eof?=false lineno=1"
* "position=23 eof?=false lineno=2"
* "position=24 eof?=false lineno=3"
* "position=36 eof?=false lineno=4"
* "position=47 eof?=true lineno=5"
*
* Unlike the stream's {position}[rdoc-ref:IO@Position],
* the line number does not affect where the next read or write will occur:
*
* f = File.new('t.txt')
* f.lineno = 1000
* f.lineno # => 1000
* f.gets # => "First line\n"
* f.lineno # => 1001
* f.close
*
* Associated with the line number is the global variable <tt>$.</tt>:
*
* - When a stream is opened, <tt>$.</tt> is not set;
* its value is left over from previous activity in the process:
*
* $. = 41
* f = File.new('t.txt')
* $. = 41
* # => 41
* f.close
*
* - When a stream is read, <tt>#.</tt> is set to the line number for that stream:
*
* f0 = File.new('t.txt')
* f1 = File.new('t.dat')
* f0.readlines # => ["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"]
* $. # => 5
* f1.readlines # => ["\xFE\xFF\x99\x90\x99\x91\x99\x92\x99\x93\x99\x94"]
* $. # => 1
* f0.close
* f1.close
*
* - Methods IO#rewind and IO#seek do not affect <tt>$.</tt>:
*
* f = File.new('t.txt')
* f.readlines # => ["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"]
* $. # => 5
* f.rewind
* f.seek(0, :SET)
* $. # => 5
* f.close
*
* == Character \IO
*
* You can process an \IO stream character-by-character using these methods:
*
* - IO#getc: Reads and returns the next character from the stream.
* - IO#readchar: Like #getc, but raises an exception at end-of-stream.
* - IO#ungetc: Pushes back ("unshifts") a character or integer onto the stream.
* - IO#putc: Writes a character to the stream.
* - IO#each_char: Reads each remaining character in the stream,
* passing the character to the given block.
* == Byte \IO
*
* You can process an \IO stream byte-by-byte using these methods:
*
* - IO#getbyte: Returns the next 8-bit byte as an integer in range 0..255.
* - IO#readbyte: Like #getbyte, but raises an exception if at end-of-stream.
* - IO#ungetbyte: Pushes back ("unshifts") a byte back onto the stream.
* - IO#each_byte: Reads each remaining byte in the stream,
* passing the byte to the given block.
*
* == Codepoint \IO
*
* You can process an \IO stream codepoint-by-codepoint:
*
* - IO#each_codepoint: Reads each remaining codepoint, passing it to the given block.
*
* == What's Here
*
* First, what's elsewhere. \Class \IO:
@ -14772,11 +15096,11 @@ set_LAST_READ_LINE(VALUE val, ID _x, VALUE *_y)
* - #read_nonblock: the next _n_ bytes read from +self+ for a given _n_,
* in non-block mode.
* - #readbyte: Returns the next byte read from +self+;
* same as #getbyte, but raises an exception on end-of-file.
* same as #getbyte, but raises an exception on end-of-stream.
* - #readchar: Returns the next character read from +self+;
* same as #getc, but raises an exception on end-of-file.
* same as #getc, but raises an exception on end-of-stream.
* - #readline: Returns the next line read from +self+;
* same as #getline, but raises an exception of end-of-file.
* same as #getline, but raises an exception of end-of-stream.
* - #readlines: Returns an array of all lines read read from +self+.
* - #readpartial: Returns up to the given number of bytes from +self+.
*
@ -14836,7 +15160,7 @@ set_LAST_READ_LINE(VALUE val, ID _x, VALUE *_y)
* - #binmode?: Returns whether +self+ is in binary mode.
* - #close_on_exec?: Returns the close-on-exec flag for +self+.
* - #closed?: Returns whether +self+ is closed.
* - #eof? (aliased as #eof): Returns whether +self+ is at end-of-file.
* - #eof? (aliased as #eof): Returns whether +self+ is at end-of-stream.
* - #external_encoding: Returns the external encoding object for +self+.
* - #fileno (aliased as #to_i): Returns the integer file descriptor for +self+
* - #internal_encoding: Returns the internal encoding object for +self+.