Reads maxlen bytes from ios using the pread system call and returns them as a string without modifying the underlying descriptor offset. This is advantageous compared to combining IO#seek and IO#read in that it is atomic, allowing multiple threads/process to share the same IO object for reading the file at various locations. This bypasses any userspace buffering of the IO layer. If the optional outbuf argument is present, it must reference a String, which will receive the data. Raises SystemCallError on error, EOFError at end of file and NotImplementedError if platform does not implement the system call.
File.write("testfile", "This is line one\nThis is line two\n") File.open("testfile") do |f| p f.read # => "This is line one\nThis is line two\n" p f.pread(12, 0) # => "This is line" p f.pread(9, 8) # => "line one\n" end
Reads all of the lines in ios, and returns them in an array. Lines are separated by the optional sep. If sep is nil, the rest of the stream is returned as a single record. If the first argument is an integer, or an optional second argument is given, the returning string would not be longer than the given value in bytes. The stream must be opened for reading or an IOError will be raised.
f = File.new("testfile") f.readlines[0] #=> "This is line one\n" f = File.new("testfile", chomp: true) f.readlines[0] #=> "This is line one"
See IO.readlines for details about getline_args.
Reads at most maxlen bytes from the I/O stream. It blocks only if ios has no data immediately available. It doesn’t block if some data available.
If the optional outbuf argument is present, it must reference a String, which will receive the data. The outbuf will contain only the received data after the method call even if it is not empty at the beginning.
It raises EOFError on end of file.
readpartial is designed for streams such as pipe, socket, tty, etc. It blocks only when no data immediately available. This means that it blocks only when following all conditions hold.
the byte buffer in the IO object is empty.
the content of the stream is empty.
the stream is not reached to EOF.
When readpartial blocks, it waits data or EOF on the stream. If some data is reached, readpartial returns with the data. If EOF is reached, readpartial raises EOFError.
When readpartial doesn’t blocks, it returns or raises immediately. If the byte buffer is not empty, it returns the data in the buffer. Otherwise if the stream has some content, it returns the data in the stream. Otherwise if the stream is reached to EOF, it raises EOFError.
r, w = IO.pipe # buffer pipe content w << "abc" # "" "abc". r.readpartial(4096) #=> "abc" "" "" r.readpartial(4096) # blocks because buffer and pipe is empty. r, w = IO.pipe # buffer pipe content w << "abc" # "" "abc" w.close # "" "abc" EOF r.readpartial(4096) #=> "abc" "" EOF r.readpartial(4096) # raises EOFError r, w = IO.pipe # buffer pipe content w << "abc\ndef\n" # "" "abc\ndef\n" r.gets #=> "abc\n" "def\n" "" w << "ghi\n" # "def\n" "ghi\n" r.readpartial(4096) #=> "def\n" "" "ghi\n" r.readpartial(4096) #=> "ghi\n" "" ""
Note that readpartial behaves similar to sysread. The differences are:
If the byte buffer is not empty, read from the byte buffer instead of “sysread for buffered IO (IOError)”.
It doesn’t cause Errno::EWOULDBLOCK and Errno::EINTR. When readpartial meets EWOULDBLOCK and EINTR by read system call, readpartial retry the system call.
The latter means that readpartial is nonblocking-flag insensitive. It blocks on the situation IO#sysread causes Errno::EWOULDBLOCK as if the fd is blocking mode.
Reads length bytes from the I/O stream.
length must be a non-negative integer or nil.
If length is a positive integer, read tries to read length bytes without any conversion (binary mode). It returns nil if an EOF is encountered before anything can be read. Fewer than length bytes are returned if an EOF is encountered during the read. In the case of an integer length, the resulting string is always in ASCII-8BIT encoding.
If length is omitted or is nil, it reads until EOF and the encoding conversion is applied, if applicable. A string is returned even if EOF is encountered before any data is read.
If length is zero, it returns an empty string ("").
If the optional outbuf argument is present, it must reference a String, which will receive the data. The outbuf will contain only the received data after the method call even if it is not empty at the beginning.
When this method is called at end of file, it returns nil or "", depending on length: read, read(nil), and read(0) return "", read(positive_integer) returns nil.
f = File.new("testfile") f.read(16) #=> "This is line one" # read whole file open("file") do |f| data = f.read # This returns a string even if the file is empty. # ... end # iterate over fixed length records open("fixed-record-file") do |f| while record = f.read(256) # ... end end # iterate over variable length records, # each record is prefixed by its 32-bit length open("variable-record-file") do |f| while len = f.read(4) len = len.unpack("N")[0] # 32-bit length record = f.read(len) # This returns a string even if len is 0. end end
Note that this method behaves like the fread() function in C. This means it retries to invoke read(2) system calls to read data with the specified length (or until EOF). This behavior is preserved even if ios is in non-blocking mode. (This method is non-blocking flag insensitive as other methods.) If you need the behavior like a single read(2) system call, consider readpartial, read_nonblock, and sysread.
Reads a line as with IO#gets, but raises an EOFError on end of file.
Reads a one-character string from ios. Raises an EOFError on end of file.
f = File.new("testfile") f.readchar #=> "h" f.readchar #=> "e"
Reads a byte as with IO#getbyte, but raises an EOFError on end of file.
Positions ios to the beginning of input, resetting lineno to zero.
f = File.new("testfile") f.readline #=> "This is line one\n" f.rewind #=> 0 f.lineno #=> 0 f.readline #=> "This is line one\n"
Note that it cannot be used with streams such as pipes, ttys, and sockets.
Returns true if the underlying file descriptor of ios will be closed automatically at its finalization, otherwise false.
Sets auto-close flag.
f = open("/dev/null") IO.for_fd(f.fileno) # ... f.gets # may cause IOError f = open("/dev/null") IO.for_fd(f.fileno).autoclose = true # ... f.gets # won't cause IOError
Returns an integer representing the numeric file descriptor for ios.
$stdin.fileno #=> 0 $stdout.fileno #=> 1
Deletes every key-value pair from gdbm for which block evaluates to true.
Returns a hash copy of gdbm where all key-value pairs from gdbm for which block evaluates to true are removed. See also: delete_if
Replaces the content of gdbm with the key-value pairs of other. other must have an each_pair method.
Turns the database’s fast mode on or off. If fast mode is turned on, gdbm does not wait for writes to be flushed to the disk before continuing.
This option is obsolete for gdbm >= 1.8 since fast mode is turned on by default. See also: syncmode=
Returns an array of all key-value pairs contained in the database.
Converts the OpenStruct to a hash with keys representing each attribute (as symbols) and their corresponding values.
If a block is given, the results of the block on each pair of the receiver will be used as pairs.
require "ostruct" data = OpenStruct.new("country" => "Australia", :capital => "Canberra") data.to_h # => {:country => "Australia", :capital => "Canberra" } data.to_h {|name, value| [name.to_s, value.upcase] } # => {"country" => "AUSTRALIA", "capital" => "CANBERRA" }
Iterates over the range, passing each nth element to the block. If begin and end are numeric, n is added for each iteration. Otherwise step invokes succ to iterate through range elements.
If no block is given, an enumerator is returned instead. Especially, the enumerator is an Enumerator::ArithmeticSequence if begin and end of the range are numeric.
range = Xs.new(1)..Xs.new(10) range.step(2) {|x| puts x} puts range.step(3) {|x| puts x}
produces:
1 x 3 xxx 5 xxxxx 7 xxxxxxx 9 xxxxxxxxx 1 x 4 xxxx 7 xxxxxxx 10 xxxxxxxxxx
See Range for the definition of class Xs.
Returns the first object in the range, or an array of the first n elements.
(10..20).first #=> 10 (10..20).first(3) #=> [10, 11, 12]
Returns the last object in the range, or an array of the last n elements.
Note that with no arguments last will return the object that defines the end of the range even if exclude_end? is true.
(10..20).last #=> 20 (10...20).last #=> 20 (10..20).last(3) #=> [18, 19, 20] (10...20).last(3) #=> [17, 18, 19]
Returns an array containing the items in the range.
(1..7).to_a #=> [1, 2, 3, 4, 5, 6, 7] (1..).to_a #=> RangeError: cannot convert endless range to an array
Convert this range object to a printable form (using to_s to convert the begin and end objects).
Returns a string containing the regular expression and its options (using the (?opts:source) notation. This string can be fed back in to Regexp::new to a regular expression with the same semantics as the original. (However, Regexp#== may not return true when comparing the two, as the source of the regular expression itself may differ, as the example shows). Regexp#inspect produces a generally more readable version of rxp.
r1 = /ab+c/ix #=> /ab+c/ix s1 = r1.to_s #=> "(?ix-m:ab+c)" r2 = Regexp.new(s1) #=> /(?ix-m:ab+c)/ r1 == r2 #=> false r1.source #=> "ab+c" r2.source #=> "(?ix-m:ab+c)"