IO

Synonym for IO::new.

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...

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

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

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.

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>

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)>

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 "

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"

See Kernel#select.

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

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

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

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

produces:

   Hello world!

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.

Returns an enumerator that gives each byte (0..255) in ios. The stream must be opened for reading or an IOError will be raised.

   f = File.new("testfile")
   f.bytes.to_a  #=> [104, 101, 108, 108, 111]
   f.rewind
   f.bytes.sort  #=> [101, 104, 108, 108, 111]

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. Multibyte characters are dealt with according to $KCODE.

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

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 $?.

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

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

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

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...

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

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. Multibyte characters are dealt with according to $KCODE.

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

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...

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?.

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?.

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.

Returns an integer representing the numeric file descriptor for ios.

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

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

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.

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

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

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"

Return a string describing this IO object.

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.

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

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

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

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

Returns an enumerator that gives each line in ios. The stream must be opened for reading or an IOError will be raised.

   f = File.new("testfile")
   f.lines.to_a  #=> ["foo\n", "bar\n"]
   f.rewind
   f.lines.sort  #=> ["bar\n", "foo\n"]

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

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

Seeks to the given position (in bytes) in ios.

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

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.

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

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

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

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"

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.

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

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.

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

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

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"

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.

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"

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"

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]

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"

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

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

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)

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"

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."

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

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

Alias for fileno

Returns ios.

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

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

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

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

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.