Ruby/Справочник/IO
Класс IO
[править]Class IO Является базовым для ввода и вывода в 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 class File, the only standard subclass of IO. The two classes are closely associated. As used in this section, portname may take any of the following forms.
- 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.
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::SEPARATOR can be used to get the platform-specific separator character. I/O ports may be opened in any one of several different modes, which are shown in this section as mode. The mode may either be a Fixnum or a String. If numeric, it should be one of the operating system specific constants (O_RDONLY, O_WRONLY, O_RDWR, O_APPEND and so on). See man open(2) for more information. If the mode is given as a String, it must be one of the values listed in the following table.
Mode | Meaning
-----+--------------------------------------------------------
"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, starts at end of file if file exists,
| otherwise creates a new file for writing.
-----+--------------------------------------------------------
"a+" | Read-write, starts at end of file if file exists,
| otherwise creates a new file for reading and
| writing.
-----+--------------------------------------------------------
"b" | (DOS/Windows only) Binary file mode (may appear with
| any of the key letters listed above).
The global constant ARGF (also accessible as $<) provides an IO-like stream which allows access to all files mentioned on the command line (or STDIN if no files are mentioned). ARGF provides the methods #path and #filename to access the name of the file currently being read.
Примеси
Enumerable (all?, any?, collect, detect, each_cons, each_slice, each_with_index, entries, enum_cons, enum_slice, enum_with_index, find, find_all, grep, group_by, include?, index_by, inject, map, max, member?, min, partition, reject, select, sort, sort_by, sum, to_a, to_set, zip),
Константы
SEEK_CUR, SEEK_END, SEEK_SET
Методы класса
for_fd, foreach, new, new, open, pipe, popen, readlines, read, select, sysopen
Методы объекта
<<, binmode, block_scanf, close_read, close_write, closed?, close, each_byte, each_line, each, eof?, eof, fcntl, fileno, flush, fsync, getc, gets, inspect, ioctl, isatty, lineno=, lineno, pid, pos=, pos, printf, print, putc, puts, read_nonblock, readbytes, readchar, readlines, readline, readpartial, read, reopen, rewind, scanf, seek, soak_up_spaces, stat, sync=, sync, sysread, sysseek, syswrite, tell, to_io, to_i, tty?, ungetc, write_nonblock, write
IO::for_fd
[править]IO.for_fd(fd, mode) => io
Synonym for IO::new.
IO::foreach
[править] IO.foreach(name, sep_string=$/) {|line| block } => nil
Executes the block for every line in the named I/O port, where lines are separated by sep_string.
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...
IO::new
[править]IO.new(fd, mode_string) => io
Returns a new IO object (a stream) for the given integer file descriptor and mode string. See also IO#fileno and IO::for_fd.
a = IO.new(2,"w") # '2' is standard error
$stderr.puts "Hello"
a.puts "World"
produces:
Hello
World
IO::new
[править]IO.new(fd, mode_string) => io
Returns a new IO object (a stream) for the given integer file descriptor and mode string. See also IO#fileno and IO::for_fd.
a = IO.new(2,"w") # '2' is standard error
$stderr.puts "Hello"
a.puts "World"
produces:
Hello
World
IO::open
[править] IO.open(fd, mode_string="r" ) => io
IO.open(fd, mode_string="r" ) {|io| block } => obj
With no associated block, 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.
IO::pipe
[править]IO.pipe -> array
Creates a pair of pipe endpoints (connected to each other) and returns them as a two-element array of IO objects: [ read_file, write_file ]. Not available on all platforms. 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>
IO::popen
[править] IO.popen(cmd_string, mode="r" ) => io
IO.popen(cmd_string, mode="r" ) {|io| block } => obj
Runs the specified command string as a subprocess; the subprocess's standard input and output will be connected to the returned IO object. If cmd_string starts with a ``-, then a new instance of Ruby is started as the subprocess. 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. 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 close the pipe and sets $?. In this case IO::popen returns the value of the block. If a block is given with a cmd_string 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
puts "Parent is #{Process.pid}"
IO.popen ("date") { |f| puts f.gets }
IO.popen("-") {|f| $stderr.puts "#{Process.pid} is here, f is #{f}"}
p $?
produces:
["Linux\n"]
Parent is 26166
Wed Apr 9 08:53:52 CDT 2003
26169 is here, f is
26166 is here, f is #<IO:0x401b3d44>
#<Process::Status: pid=26166,exited(0)>
IO::read
[править]IO.read(name, [length [, offset]] ) => string
Opens the file, optionally seeks to the given offset, then returns length bytes (defaulting to the rest of the file). read ensures the file is closed before returning.
IO.read("testfile") #=> "This is line one\nThis is line two\nThis is line three\nAnd so on...\n"
IO.read("testfile", 20) #=> "This is line one\nThi"
IO.read("testfile", 20, 10) #=> "ne one\nThis is line "
IO::readlines
[править]IO.readlines(name, sep_string=$/) => array
Reads the entire file specified by name as individual lines, and returns those lines in an array. Lines are separated by sep_string.
a = IO.readlines("testfile")
a[0] #=> "This is line one\n"
IO::select
[править]IO.select(read_array [, write_array [, error_array [, timeout]]] ) => array or nil
See Kernel#select.
IO::sysopen
[править]IO.sysopen(path, [mode, [perm]]) => fixnum
Opens the given path, returning the underlying file descriptor as a Fixnum.
IO.sysopen("testfile") #=> 3
IO#<<
[править]ios << obj => ios
String Output---Writes obj to ios. obj will be converted to a string using to_s.
$stdout << "Hello " << "world!\n"
produces:
Hello world!
IO#binmode
[править]ios.binmode => ios
Puts ios into binary mode. This is useful only in MS-DOS/Windows environments. Once a stream is in binary mode, it cannot be reset to nonbinary mode.
IO#block_scanf
[править] block_scanf(str) {|current| ...}
(нет описания...)
IO#close
[править]ios.close => nil
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 $?.
IO#close_read
[править]ios.close_read => nil
Closes the read end of a duplex I/O stream (i.e., one that contains both a read and a write stream, such as a pipe). Will raise an IOError if the stream is not duplexed.
f = IO.popen("/bin/sh","r+")
f.close_read
f.readlines
produces:
prog.rb:3:in `readlines': not opened for reading (IOError)
from prog.rb:3
IO#close_write
[править]ios.close_write => nil
Closes the write end of a duplex I/O stream (i.e., one that contains both a read and a write stream, such as a pipe). Will raise an IOError if the stream is not duplexed.
f = IO.popen("/bin/sh","r+")
f.close_write
f.print "nowhere"
produces:
prog.rb:3:in `write': not opened for writing (IOError)
from prog.rb:3:in `print'
from prog.rb:3
IO#closed?
[править]ios.closed? => true or false
Returns true if ios is completely closed (for duplex streams, both reader and writer), false otherwise.
f = File.new("testfile")
f.close #=> nil
f.closed? #=> true
f = IO.popen("/bin/sh","r+")
f.close_write #=> nil
f.closed? #=> false
f.close_read #=> nil
f.closed? #=> true
IO#each
[править] ios.each(sep_string=$/) {|line| block } => ios
ios.each_line(sep_string=$/) {|line| block } => ios
Executes the block for every line in ios, where lines are separated by sep_string. ios must be opened for reading or an IOError will be raised.
f = File.new("testfile")
f.each {|line| puts "#{f.lineno}: #{line}" }
produces:
1: This is line one
2: This is line two
3: This is line three
4: And so on...
IO#each_byte
[править] ios.each_byte {|byte| block } => nil
Calls the given block once for each byte (0..255) in ios, passing the byte as an argument. The stream must be opened for reading or an IOError will be raised.
f = File.new("testfile")
checksum = 0
f.each_byte {|x| checksum ^= x } #=> #<File:testfile>
checksum #=> 12
IO#each_line
[править] ios.each(sep_string=$/) {|line| block } => ios
ios.each_line(sep_string=$/) {|line| block } => ios
Executes the block for every line in ios, where lines are separated by sep_string. ios must be opened for reading or an IOError will be raised.
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...
IO#eof
[править]ios.eof => true or false ios.eof? => true or false
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 a input buffer. So IO#sysread doesn't work with IO#eof?.
IO#eof?
[править]ios.eof => true or false ios.eof? => true or false
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 a input buffer. So IO#sysread doesn't work with IO#eof?.
IO#fcntl
[править]ios.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.
IO#fileno
[править]ios.fileno => fixnum ios.to_i => fixnum
Returns an integer representing the numeric file descriptor for ios.
$stdin.fileno #=> 0
$stdout.fileno #=> 1
(еще известен как to_i)
IO#flush
[править]ios.flush => ios
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"
$stdout.flush
produces:
no newline
IO#fsync
[править]ios.fsync => 0 or nil
Immediately writes all buffered data in ios to disk. Returns nil if the underlying operating system does not support fsync(2). Note that fsync differs from using IO#sync=. The latter ensures that data is flushed from Ruby's buffers, but doesn't not guarantee that the underlying operating system actually writes it to disk.
IO#getc
[править]ios.getc => fixnum or nil
Gets the next 8-bit byte (0..255) from ios. Returns nil if called at end of file.
f = File.new("testfile")
f.getc #=> 84
f.getc #=> 104
IO#gets
[править]ios.gets(sep_string=$/) => string or nil
Reads the next ``line from the I/O stream; lines are separated by sep_string. 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.
File.new("testfile").gets #=> "This is line one\n"
$_ #=> "This is line one\n"
IO#inspect
[править]ios.inspect => string
Return a string describing this IO object.
IO#ioctl
[править]ios.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.
IO#isatty
[править]ios.isatty => true or false ios.tty? => true or false
Returns true if ios is associated with a terminal device (tty), false otherwise.
File.new("testfile").isatty #=> false
File.new("/dev/tty").isatty #=> true
IO#lineno
[править]ios.lineno => integer
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. 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
IO#lineno=
[править]ios.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
$. # lineno of last read #=> 1
f.gets #=> "This is line two\n"
$. # lineno of last read #=> 1001
IO#pid
[править]ios.pid => fixnum
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
IO#pos
[править]ios.pos => integer ios.tell => integer
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
IO#pos=
[править]ios.pos = integer => integer
Seeks to the given position (in bytes) in ios.
f = File.new("testfile")
f.pos = 17
f.gets #=> "This is line two\n"
IO#print
[править]ios.print() => nil ios.print(obj, ...) => nil
Writes the given object(s) to ios. The stream must be opened for writing. If the output record separator ($\) is not nil, it will be appended to the output. If no arguments are given, prints $_. Objects that aren't strings will be converted by calling their to_s method. With no argument, prints the contents of the variable $_. Returns nil.
$stdout.print("This is ", 100, " percent.\n")
produces:
This is 100 percent.
IO#printf
[править]ios.printf(format_string [, obj, ...] ) => nil
Formats and writes to ios, converting parameters under control of the format string. See Kernel#sprintf for details.
IO#putc
[править]ios.putc(obj) => obj
If obj is Numeric, write the character whose code is obj, otherwise write the first character of the string representation of obj to ios.
$stdout.putc "A"
$stdout.putc 65
produces:
AA
IO#puts
[править]ios.puts(obj, ...) => nil
Writes the given objects to ios as with IO#print. Writes a record separator (typically a newline) after any that do not already end with a newline sequence. If called with an array argument, writes each element on a new line. If called without arguments, outputs a single record separator.
$stdout.puts("this", "is", "a", "test")
produces:
this
is
a
test
IO#read
[править]ios.read([length [, buffer]]) => string, buffer, or nil
Reads at most length bytes from the I/O stream, or to the end of file if length is omitted or is nil. length must be a non-negative integer or nil. If the optional buffer argument is present, it must reference a String, which will receive the data. At end of file, it returns nil or "" depend on length. ios.read() and ios.read(nil) returns "". ios.read(positive-integer) returns nil.
f = File.new("testfile")
f.read(16) #=> "This is line one"
IO#read_nonblock
[править]ios.read_nonblock(maxlen) => string ios.read_nonblock(maxlen, outbuf) => outbuf
Reads at most maxlen bytes from ios using read(2) system call after O_NONBLOCK is set for the underlying file descriptor. If the optional outbuf argument is present, it must reference a String, which will receive the data. read_nonblock just calls read(2). It causes all errors read(2) causes: EAGAIN, EINTR, etc. The caller should care such errors. read_nonblock causes EOFError on EOF. If the read buffer is not empty, read_nonblock reads from the buffer like readpartial. In this case, read(2) is not called.
IO#readbytes
[править]readbytes(n)
Reads exactly n bytes. If the data read is nil an EOFError is raised. If the data read is too short a TruncatedDataError is raised and the read data is obtainable via its #data method.
IO#readchar
[править]ios.readchar => fixnum
Reads a character as with IO#getc, but raises an EOFError on end of file.
IO#readline
[править]ios.readline(sep_string=$/) => string
Reads a line as with IO#gets, but raises an EOFError on end of file.
IO#readlines
[править]ios.readlines(sep_string=$/) => array
Reads all of the lines in ios, and returns them in anArray. Lines are separated by the optional sep_string. If sep_string is nil, the rest of the stream is returned as a single record. 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"
IO#readpartial
[править]ios.readpartial(maxlen) => string ios.readpartial(maxlen, outbuf) => outbuf
Reads at most maxlen bytes from the I/O stream. It blocks only if ios has no data immediately available. It doesn't block if some data available. If the optional outbuf argument is present, it must reference a String, which will receive the data. 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 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 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 buffer is not empty, read from the buffer instead of "sysread for buffered IO (IOError)".
- It doesn't cause Errno::EAGAIN and Errno::EINTR. When readpartial meets EAGAIN and EINTR by read system call, readpartial retry the system call.
The later means that readpartial is nonblocking-flag insensitive. It blocks on the situation IO#sysread causes Errno::EAGAIN as if the fd is blocking mode.
IO#reopen
[править]ios.reopen(other_IO) => ios ios.reopen(path, mode_str) => ios
Reassociates ios with the I/O stream given in other_IO or to a new stream opened on path. This may dynamically change the actual class of this stream.
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"
IO#rewind
[править]ios.rewind => 0
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"
IO#scanf
[править]scanf(str,&b)
The trick here is doing a match where you grab one line of input at a time. The linebreak may or may not occur at the boundary where the string matches a format specifier. And if it does, some rule about whitespace may or may not be in effect... That's why this is much more elaborate than the string version. For each line: Match succeeds (non-emptily) and the last attempted spec/string sub-match succeeded:
could the last spec keep matching?
yes: save interim results and continue (next line)
The last attempted spec/string did not match: are we on the next-to-last spec in the string?
yes:
is fmt_string.string_left all spaces?
yes: does current spec care about input space?
yes: fatal failure
no: save interim results and continue
no: continue [this state could be analyzed further]
IO#seek
[править]ios.seek(amount, whence=SEEK_SET) -> 0
Seeks to a given offset anInteger in the stream according to the value of whence:
IO::SEEK_CUR | Seeks to amount plus current position
--------------+----------------------------------------------------
IO::SEEK_END | Seeks to amount plus end of stream (you probably
| want a negative value for amount)
--------------+----------------------------------------------------
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"
IO#soak_up_spaces
[править]soak_up_spaces()
(нет описания...)
IO#stat
[править]ios.stat => stat
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
IO#sync
[править]ios.sync => true or false
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
IO#sync=
[править]ios.sync = boolean => boolean
Sets the ``sync mode to true or false. When sync mode is true, all output is immediately flushed to the underlying operating system and is not buffered internally. Returns the new state. See also IO#fsync.
f = File.new("testfile")
f.sync = true
(produces no output)
IO#sysread
[править]ios.sysread(integer ) => string
Reads integer 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. Raises SystemCallError on error and EOFError at end of file.
f = File.new("testfile")
f.sysread(16) #=> "This is line one"
IO#sysseek
[править]ios.sysseek(offset, whence=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."
IO#syswrite
[править]ios.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
IO#tell
[править]ios.pos => integer ios.tell => integer
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
IO#to_i
[править]to_i()
Alias for #fileno
IO#to_io
[править]ios.to_io -> ios
Returns ios.
IO#tty?
[править]ios.isatty => true or false ios.tty? => true or false
Returns true if ios is associated with a terminal device (tty), false otherwise.
File.new("testfile").isatty #=> false
File.new("/dev/tty").isatty #=> true
IO#ungetc
[править]ios.ungetc(integer) => nil
Pushes back one character (passed as a parameter) onto ios, such that a subsequent buffered 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 #=> 84
f.ungetc(c) #=> nil
f.getc #=> 84
IO#write
[править]ios.write(string) => integer
Writes the given string to ios. The stream must be opened for writing. If the argument is not a string, it will be converted to a string using to_s. Returns the number of bytes written.
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
IO#write_nonblock
[править]ios.write_nonblock(string) => integer
Writes the given string to ios using write(2) system call after O_NONBLOCK is set for the underlying file descriptor. write_nonblock just calls write(2). It causes all errors write(2) causes: EAGAIN, EINTR, etc. The result may also be smaller than string.length (partial write). The caller should care such errors and partial write.