Elixir v1.2.6 IO
Functions handling IO.
Many functions in this module expect an IO device as an argument.
An IO device must be a pid or an atom representing a process.
For convenience, Elixir provides :stdio and :stderr as
shortcuts to Erlang’s :standard_io and :standard_error.
The majority of the functions expect char data, i.e. strings or
lists of characters and strings. In case another type is given,
functions will convert to string via the String.Chars protocol
(as shown in typespecs).
The functions starting with bin* expect iodata as an argument,
i.e. binaries or lists of bytes and binaries.
IO devices
An IO device may be an atom or a pid. In case it is an atom, the atom must be the name of a registered process. In addition, Elixir provides two shorcuts:
:stdio- a shortcut for:standard_io, which maps to the currentProcess.group_leader/0in Erlang:stderr- a shortcut for the named process:standard_errorprovided in Erlang
IO devices maintain their position, that means subsequent calls to any
reading or writing functions will start from the place when the device
was last accessed. Position of files can be changed using the
:file.position/2 function.
Summary
Functions
Reads count characters from the IO device, a whole
:line or the whole device with :all
Converts the IO device into a IO.Stream
Writes the given argument to the given device as a binary, no unicode conversion happens
Converts chardata (a list of integers representing codepoints, lists and strings) into a string
Gets a number of bytes from the io device. If the
io device is a unicode device, count implies
the number of unicode codepoints to be retrieved.
Otherwise, count is the number of raw bytes to be retrieved.
It returns
Gets a number of bytes from the io device. If the
io device is a unicode device, count implies
the number of unicode codepoints to be retrieved.
Otherwise, count is the number of raw bytes to be retrieved
Reads a line from the IO device
Inspects and writes the given argument to the device
Inspects the item with options using the given device
Returns the size of an iodata
Converts iodata (a list of integers representing bytes, lists and binaries) into a binary
Writes the argument to the device, similar to write/2,
but adds a newline at the end. The argument is expected
to be a chardata
Reads count characters from the IO device, a whole
:line or the whole device with :all
Converts the io device into a IO.Stream
Writes the given argument to the given device
Types
Functions
Reads count characters from the IO device, a whole
:line or the whole device with :all.
It returns:
data- the input characters:eof- end of file was encountered{:error, reason}- other (rare) error condition; for instance,{:error, :estale}if reading from an NFS volume
If :all is given, :eof is never returned, but an
empty string in case the device has reached EOF.
Note: do not use this function on IO devices in unicode mode as it will return the wrong result.
Converts the IO device into a IO.Stream.
An IO.Stream implements both Enumerable and
Collectable, allowing it to be used for both read
and write.
The device is iterated line by line or by a number of bytes. This reads the IO device as a raw binary.
Note that an IO stream has side effects and every time you go over the stream you may get different results.
Finally, do not use this function on IO devices in unicode mode as it will return the wrong result.
Writes the given argument to the given device as a binary, no unicode conversion happens.
Check write/2 for more information.
Note: do not use this function on IO devices in unicode mode as it will return the wrong result.
Converts chardata (a list of integers representing codepoints, lists and strings) into a string.
In case the conversion fails, it raises a UnicodeConversionError.
If a string is given, returns the string itself.
Examples
iex> IO.chardata_to_string([0x00E6, 0x00DF])
"æß"
iex> IO.chardata_to_string([0x0061, "bc"])
"abc"getn(chardata | String.Chars.t, pos_integer) :: chardata | nodata
getn(device, chardata | String.Chars.t) :: chardata | nodata
Gets a number of bytes from the io device. If the
io device is a unicode device, count implies
the number of unicode codepoints to be retrieved.
Otherwise, count is the number of raw bytes to be retrieved.
It returns:
data- the input characters:eof- end of file was encountered{:error, reason}- other (rare) error condition; for instance,{:error, :estale}if reading from an NFS volume
getn(device, chardata | String.Chars.t, pos_integer) :: chardata | nodata
Gets a number of bytes from the io device. If the
io device is a unicode device, count implies
the number of unicode codepoints to be retrieved.
Otherwise, count is the number of raw bytes to be retrieved.
Reads a line from the IO device.
It returns:
data- the characters in the line terminated by a line-feed (LF) or end of file (EOF):eof- end of file was encountered{:error, reason}- other (rare) error condition; for instance,{:error, :estale}if reading from an NFS volume
Examples
To display “What is your name?” as a prompt and await user input:
IO.gets "What is your name?"Inspects and writes the given argument to the device.
It enables pretty printing by default with width of
80 characters. The width can be changed by explicitly
passing the :width option.
See Inspect.Opts for a full list of options.
Examples
IO.inspect Process.list, width: 40Inspects the item with options using the given device.
See Inspect.Opts for a full list of options.
Returns the size of an iodata.
Inlined by the compiler.
Examples
iex> IO.iodata_length([1, 2|<<3, 4>>])
4Converts iodata (a list of integers representing bytes, lists and binaries) into a binary.
Notice that this function treats lists of integers as raw bytes
and does not perform any kind of encoding conversion. If you want
to convert from a char list to a string (UTF-8 encoded), please
use chardata_to_string/1 instead.
If this function receives a binary, the same binary is returned.
Inlined by the compiler.
Examples
iex> bin1 = <<1, 2, 3>>
iex> bin2 = <<4, 5>>
iex> bin3 = <<6>>
iex> IO.iodata_to_binary([bin1, 1, [2, 3, bin2], 4|bin3])
<<1, 2, 3, 1, 2, 3, 4, 5, 4, 6>>
iex> bin = <<1, 2, 3>>
iex> IO.iodata_to_binary(bin)
<<1, 2, 3>>Writes the argument to the device, similar to write/2,
but adds a newline at the end. The argument is expected
to be a chardata.
Reads count characters from the IO device, a whole
:line or the whole device with :all.
It returns:
data- the input characters:eof- end of file was encountered{:error, reason}- other (rare) error condition; for instance,{:error, :estale}if reading from an NFS volume
If :all is given, :eof is never returned, but an
empty string in case the device has reached EOF.
Converts the io device into a IO.Stream.
An IO.Stream implements both Enumerable and
Collectable, allowing it to be used for both read
and write.
The device is iterated line by line if :line is given or
by a given number of codepoints.
This reads the IO as utf-8. Check out
IO.binstream/2 to handle the IO as a raw binary.
Note that an IO stream has side effects and every time you go over the stream you may get different results.
Examples
Here is an example on how we mimic an echo server from the command line:
Enum.each IO.stream(:stdio, :line), &IO.write(&1)