file

file(3)                    Erlang Module Definition                    file(3)



NAME
       file - File interface module.

DESCRIPTION
       This module provides an interface to the file system.

   Warning:
       File operations are only guaranteed to appear atomic when going through
       the same file server. A NIF or other OS process may observe
       intermediate steps on certain operations on some operating systems, eg.
       renaming an existing file on Windows, or write_file_info/2 on any OS at
       the time of writing.


       Regarding filename encoding, the Erlang VM can operate in two modes.
       The current mode can be queried using function native_name_encoding/0.
       It returns latin1 or utf8.

       In latin1 mode, the Erlang VM does not change the encoding of
       filenames. In utf8 mode, filenames can contain Unicode characters
       greater than 255 and the VM converts filenames back and forth to the
       native filename encoding (usually UTF-8, but UTF-16 on Windows).

       The default mode depends on the operating system. Windows and MacOS X
       enforce consistent filename encoding and therefore the VM uses utf8
       mode.

       On operating systems with transparent naming (for example, all Unix
       systems except MacOS X), default is utf8 if the terminal supports
       UTF-8, otherwise latin1. The default can be overridden using +fnl (to
       force latin1 mode) or +fnu (to force utf8 mode) when starting erl.

       On operating systems with transparent naming, files can be
       inconsistently named, for example, some files are encoded in UTF-8
       while others are encoded in ISO Latin-1. The concept of raw filenames
       is introduced to handle file systems with inconsistent naming when
       running in utf8 mode.

       A raw filename is a filename specified as a binary. The Erlang VM does
       not translate a filename specified as a binary on systems with
       transparent naming.

       When running in utf8 mode, functions list_dir/1 and read_link/1 never
       return raw filenames. To return all filenames including raw filenames,
       use functions list_dir_all/1 and read_link_all/1.

       See also section Notes About Raw Filenames in the STDLIB User's Guide.

   Note:
       File operations used to accept filenames containing null characters
       (integer value zero). This caused the name to be truncated and in some
       cases arguments to primitive operations to be mixed up. Filenames
       containing null characters inside the filename are now rejected and
       will cause primitive file operations fail.


DATA TYPES
       deep_list() = [char() | atom() | deep_list()]

       fd()

              A file descriptor representing a file opened in raw mode.

       filename() = string()

              See also the documentation of the name_all() type.

       filename_all() = string() | binary()

              See also the documentation of the name_all() type.

       io_device() = pid() | fd()

              As returned by open/2; pid() is a process handling I/O-
              protocols.

       name() = string() | atom() | deep_list()

              If VM is in Unicode filename mode, string() and char() are
              allowed to be > 255. See also the documentation of the
              name_all() type.

       name_all() =
           string() | atom() | deep_list() | (RawFilename :: binary())

              If VM is in Unicode filename mode, characters are allowed to be
              > 255. RawFilename is a filename not subject to Unicode
              translation, meaning that it can contain characters not
              conforming to the Unicode encoding expected from the file system
              (that is, non-UTF-8 characters although the VM is started in
              Unicode filename mode). Null characters (integer value zero) are
              not allowed in filenames (not even at the end).

       posix() =
           eacces | eagain | ebadf | ebadmsg | ebusy | edeadlk |
           edeadlock | edquot | eexist | efault | efbig | eftype |
           eintr | einval | eio | eisdir | eloop | emfile | emlink |
           emultihop | enametoolong | enfile | enobufs | enodev |
           enolck | enolink | enoent | enomem | enospc | enosr | enostr |
           enosys | enotblk | enotdir | enotsup | enxio | eopnotsupp |
           eoverflow | eperm | epipe | erange | erofs | espipe | esrch |
           estale | etxtbsy | exdev

              An atom that is named from the POSIX error codes used in Unix,
              and in the runtime libraries of most C compilers.

       date_time() = calendar:datetime()

              Must denote a valid date and time.

       file_info() =
           #file_info{size = integer() >= 0 | undefined,
                      type =
                          device | directory | other | regular |
                          symlink | undefined,
                      access =
                          read | write | read_write | none | undefined,
                      atime =
                          file:date_time() |
                          integer() >= 0 |
                          undefined,
                      mtime =
                          file:date_time() |
                          integer() >= 0 |
                          undefined,
                      ctime =
                          file:date_time() |
                          integer() >= 0 |
                          undefined,
                      mode = integer() >= 0 | undefined,
                      links = integer() >= 0 | undefined,
                      major_device = integer() >= 0 | undefined,
                      minor_device = integer() >= 0 | undefined,
                      inode = integer() >= 0 | undefined,
                      uid = integer() >= 0 | undefined,
                      gid = integer() >= 0 | undefined}

       location() =
           integer() |
           {bof, Offset :: integer()} |
           {cur, Offset :: integer()} |
           {eof, Offset :: integer()} |
           bof | cur | eof

       mode() =
           read | write | append | exclusive | raw | binary |
           {delayed_write,
            Size :: integer() >= 0,
            Delay :: integer() >= 0} |
           delayed_write |
           {read_ahead, Size :: integer() >= 1} |
           read_ahead | compressed |
           {encoding, unicode:encoding()} |
           sync

       file_info_option() =
           {time, local} | {time, universal} | {time, posix} | raw

EXPORTS
       advise(IoDevice, Offset, Length, Advise) -> ok | {error, Reason}

              Types:

                 IoDevice = io_device()
                 Offset = Length = integer()
                 Advise = posix_file_advise()
                 Reason = posix() | badarg
                 posix_file_advise() =
                     normal | sequential | random | no_reuse | will_need |
                     dont_need

              advise/4 can be used to announce an intention to access file
              data in a specific pattern in the future, thus allowing the
              operating system to perform appropriate optimizations.

              On some platforms, this function might have no effect.

       allocate(File, Offset, Length) -> ok | {error, posix()}

              Types:

                 File = io_device()
                 Offset = Length = integer() >= 0

              allocate/3 can be used to preallocate space for a file.

              This function only succeeds in platforms that provide this
              feature. When it succeeds, space is preallocated for the file
              but the file size might not be updated. This behaviour depends
              on the preallocation implementation. To guarantee that the file
              size is updated, truncate the file to the new size.

       change_group(Filename, Gid) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Gid = integer()
                 Reason = posix() | badarg

              Changes group of a file. See write_file_info/2.

       change_mode(Filename, Mode) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Mode = integer()
                 Reason = posix() | badarg

              Changes permissions of a file. See write_file_info/2.

       change_owner(Filename, Uid) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Uid = integer()
                 Reason = posix() | badarg

              Changes owner of a file. See write_file_info/2.

       change_owner(Filename, Uid, Gid) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Uid = Gid = integer()
                 Reason = posix() | badarg

              Changes owner and group of a file. See write_file_info/2.

       change_time(Filename, Mtime) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Mtime = date_time()
                 Reason = posix() | badarg

              Changes the modification and access times of a file. See
              write_file_info/2.

       change_time(Filename, Atime, Mtime) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Atime = Mtime = date_time()
                 Reason = posix() | badarg

              Changes the modification and last access times of a file. See
              write_file_info/2.

       close(IoDevice) -> ok | {error, Reason}

              Types:

                 IoDevice = io_device()
                 Reason = posix() | badarg | terminated

              Closes the file referenced by IoDevice. It mostly returns ok,
              except for some severe errors such as out of memory.

              Notice that if option delayed_write was used when opening the
              file, close/1 can return an old write error and not even try to
              close the file. See open/2.

       consult(Filename) -> {ok, Terms} | {error, Reason}

              Types:

                 Filename = name_all()
                 Terms = [term()]
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              Reads Erlang terms, separated by '.', from Filename. Returns one
              of the following:

                {ok, Terms}:
                  The file was successfully read.

                {error, atom()}:
                  An error occurred when opening the file or reading it. For a
                  list of typical error codes, see open/2.

                {error, {Line, Mod, Term}}:
                  An error occurred when interpreting the Erlang terms in the
                  file. To convert the three-element tuple to an English
                  description of the error, use format_error/1.

              Example:

              f.txt:  {person, "kalle", 25}.
                      {person, "pelle", 30}.

              1> file:consult("f.txt").
              {ok,[{person,"kalle",25},{person,"pelle",30}]}

              The encoding of Filename can be set by a comment, as described
              in epp(3).

       copy(Source, Destination) -> {ok, BytesCopied} | {error, Reason}

       copy(Source, Destination, ByteCount) ->
               {ok, BytesCopied} | {error, Reason}

              Types:

                 Source = Destination = io_device() | Filename | {Filename,
                 Modes}
                 Filename = name_all()
                 Modes = [mode()]
                 ByteCount = integer() >= 0 | infinity
                 BytesCopied = integer() >= 0
                 Reason = posix() | badarg | terminated

              Copies ByteCount bytes from Source to Destination. Source and
              Destination refer to either filenames or IO devices from, for
              example, open/2. ByteCount defaults to infinity, denoting an
              infinite number of bytes.

              Argument Modes is a list of possible modes, see open/2, and
              defaults to [].

              If both Source and Destination refer to filenames, the files are
              opened with [read, binary] and [write, binary] prepended to
              their mode lists, respectively, to optimize the copy.

              If Source refers to a filename, it is opened with read mode
              prepended to the mode list before the copy, and closed when
              done.

              If Destination refers to a filename, it is opened with write
              mode prepended to the mode list before the copy, and closed when
              done.

              Returns {ok, BytesCopied}, where BytesCopied is the number of
              bytes that was copied, which can be less than ByteCount if end
              of file was encountered on the source. If the operation fails,
              {error, Reason} is returned.

              Typical error reasons: as for open/2 if a file had to be opened,
              and as for read/2 and write/2.

       datasync(IoDevice) -> ok | {error, Reason}

              Types:

                 IoDevice = io_device()
                 Reason = posix() | badarg | terminated

              Ensures that any buffers kept by the operating system (not by
              the Erlang runtime system) are written to disk. In many ways it
              resembles fsync but it does not update some of the metadata of
              the file, such as the access time. On some platforms this
              function has no effect.

              Applications that access databases or log files often write a
              tiny data fragment (for example, one line in a log file) and
              then call fsync() immediately to ensure that the written data is
              physically stored on the hard disk. Unfortunately, fsync()
              always initiates two write operations: one for the newly written
              data and another one to update the modification time stored in
              the inode. If the modification time is not a part of the
              transaction concept, fdatasync() can be used to avoid
              unnecessary inode disk write operations.

              Available only in some POSIX systems, this call results in a
              call to fsync(), or has no effect in systems not providing the
              fdatasync() syscall.

       del_dir(Dir) -> ok | {error, Reason}

              Types:

                 Dir = name_all()
                 Reason = posix() | badarg

              Tries to delete directory Dir. The directory must be empty
              before it can be deleted. Returns ok if successful.

              Typical error reasons:

                eacces:
                  Missing search or write permissions for the parent
                  directories of Dir.

                eexist:
                  The directory is not empty.

                enoent:
                  The directory does not exist.

                enotdir:
                  A component of Dir is not a directory. On some platforms,
                  enoent is returned instead.

                einval:
                  Attempt to delete the current directory. On some platforms,
                  eacces is returned instead.

       delete(Filename) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Reason = posix() | badarg

              Tries to delete file Filename. Returns ok if successful.

              Typical error reasons:

                enoent:
                  The file does not exist.

                eacces:
                  Missing permission for the file or one of its parents.

                eperm:
                  The file is a directory and the user is not superuser.

                enotdir:
                  A component of the filename is not a directory. On some
                  platforms, enoent is returned instead.

                einval:
                  Filename has an improper type, such as tuple.

          Warning:
              In a future release, a bad type for argument Filename will
              probably generate an exception.


       eval(Filename) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              Reads and evaluates Erlang expressions, separated by '.' (or
              ',', a sequence of expressions is also an expression) from
              Filename. The result of the evaluation is not returned; any
              expression sequence in the file must be there for its side
              effect. Returns one of the following:

                ok:
                  The file was read and evaluated.

                {error, atom()}:
                  An error occurred when opening the file or reading it. For a
                  list of typical error codes, see open/2.

                {error, {Line, Mod, Term}}:
                  An error occurred when interpreting the Erlang expressions
                  in the file. To convert the three-element tuple to an
                  English description of the error, use format_error/1.

              The encoding of Filename can be set by a comment, as described
              in epp(3).

       eval(Filename, Bindings) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Bindings = erl_eval:binding_struct()
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              The same as eval/1, but the variable bindings Bindings are used
              in the evaluation. For information about the variable bindings,
              see erl_eval(3).

       format_error(Reason) -> Chars

              Types:

                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}
                 Chars = string()

              Given the error reason returned by any function in this module,
              returns a descriptive string of the error in English.

       get_cwd() -> {ok, Dir} | {error, Reason}

              Types:

                 Dir = filename()
                 Reason = posix()

              Returns {ok, Dir}, where Dir is the current working directory of
              the file server.

          Note:
              In rare circumstances, this function can fail on Unix. It can
              occur if read permission does not exist for the parent
              directories of the current directory.


              A typical error reason:

                eacces:
                  Missing read permission for one of the parents of the
                  current directory.

       get_cwd(Drive) -> {ok, Dir} | {error, Reason}

              Types:

                 Drive = string()
                 Dir = filename()
                 Reason = posix() | badarg

              Returns {ok, Dir} or {error, Reason}, where Dir is the current
              working directory of the specified drive.

              Drive is to be of the form "Letter:", for example, "c:".

              Returns {error, enotsup} on platforms that have no concept of
              current drive (Unix, for example).

              Typical error reasons:

                enotsup:
                  The operating system has no concept of drives.

                eacces:
                  The drive does not exist.

                einval:
                  The format of Drive is invalid.

       list_dir(Dir) -> {ok, Filenames} | {error, Reason}

              Types:

                 Dir = name_all()
                 Filenames = [filename()]
                 Reason =
                     posix() |
                     badarg |
                     {no_translation, Filename :: unicode:latin1_binary()}

              Lists all files in a directory, except files with raw filenames.
              Returns {ok, Filenames} if successful, otherwise {error,
              Reason}. Filenames is a list of the names of all the files in
              the directory. The names are not sorted.

              Typical error reasons:

                eacces:
                  Missing search or write permissions for Dir or one of its
                  parent directories.

                enoent:
                  The directory does not exist.

                {no_translation, Filename}:
                  Filename is a binary() with characters coded in ISO Latin-1
                  and the VM was started with parameter +fnue.

       list_dir_all(Dir) -> {ok, Filenames} | {error, Reason}

              Types:

                 Dir = name_all()
                 Filenames = [filename_all()]
                 Reason = posix() | badarg

              Lists all the files in a directory, including files with raw
              filenames. Returns {ok, Filenames} if successful, otherwise
              {error, Reason}. Filenames is a list of the names of all the
              files in the directory. The names are not sorted.

              Typical error reasons:

                eacces:
                  Missing search or write permissions for Dir or one of its
                  parent directories.

                enoent:
                  The directory does not exist.

       make_dir(Dir) -> ok | {error, Reason}

              Types:

                 Dir = name_all()
                 Reason = posix() | badarg

              Tries to create directory Dir. Missing parent directories are
              not created. Returns ok if successful.

              Typical error reasons:

                eacces:
                  Missing search or write permissions for the parent
                  directories of Dir.

                eexist:
                  A file or directory named Dir exists already.

                enoent:
                  A component of Dir does not exist.

                enospc:
                  No space is left on the device.

                enotdir:
                  A component of Dir is not a directory. On some platforms,
                  enoent is returned instead.

       make_link(Existing, New) -> ok | {error, Reason}

              Types:

                 Existing = New = name_all()
                 Reason = posix() | badarg

              Makes a hard link from Existing to New on platforms supporting
              links (Unix and Windows). This function returns ok if the link
              was successfully created, otherwise {error, Reason}. On
              platforms not supporting links, {error,enotsup} is returned.

              Typical error reasons:

                eacces:
                  Missing read or write permissions for the parent directories
                  of Existing or New.

                eexist:
                  New already exists.

                enotsup:
                  Hard links are not supported on this platform.

       make_symlink(Existing, New) -> ok | {error, Reason}

              Types:

                 Existing = New = name_all()
                 Reason = posix() | badarg

              Creates a symbolic link New to the file or directory Existing on
              platforms supporting symbolic links (most Unix systems and
              Windows, beginning with Vista). Existing does not need to exist.
              Returns ok if the link is successfully created, otherwise
              {error, Reason}. On platforms not supporting symbolic links,
              {error, enotsup} is returned.

              Typical error reasons:

                eacces:
                  Missing read or write permissions for the parent directories
                  of Existing or New.

                eexist:
                  New already exists.

                enotsup:
                  Symbolic links are not supported on this platform.

                eperm:
                  User does not have privileges to create symbolic links
                  (SeCreateSymbolicLinkPrivilege on Windows).

       native_name_encoding() -> latin1 | utf8

              Returns the filename encoding mode. If it is latin1, the system
              translates no filenames. If it is utf8, filenames are converted
              back and forth to the native filename encoding (usually UTF-8,
              but UTF-16 on Windows).

       open(File, Modes) -> {ok, IoDevice} | {error, Reason}

              Types:

                 File = Filename | iodata()
                 Filename = name_all()
                 Modes = [mode() | ram]
                 IoDevice = io_device()
                 Reason = posix() | badarg | system_limit

              Opens file File in the mode determined by Modes, which can
              contain one or more of the following options:

                read:
                  The file, which must exist, is opened for reading.

                write:
                  The file is opened for writing. It is created if it does not
                  exist. If the file exists and write is not combined with
                  read, the file is truncated.

                append:
                  The file is opened for writing. It is created if it does not
                  exist. Every write operation to a file opened with append
                  takes place at the end of the file.

                exclusive:
                  The file is opened for writing. It is created if it does not
                  exist. If the file exists, {error, eexist} is returned.

            Warning:
                This option does not guarantee exclusiveness on file systems
                not supporting O_EXCL properly, such as NFS. Do not depend on
                this option unless you know that the file system supports it
                (in general, local file systems are safe).


                raw:
                  Allows faster access to a file, as no Erlang process is
                  needed to handle the file. However, a file opened in this
                  way has the following limitations:

                  * The functions in the io module cannot be used, as they can
                    only talk to an Erlang process. Instead, use functions
                    read/2, read_line/1, and write/2.

                  * Especially if read_line/1 is to be used on a raw file, it
                    is recommended to combine this option with option
                    {read_ahead, Size} as line-oriented I/O is inefficient
                    without buffering.

                  * Only the Erlang process that opened the file can use it.

                  * A remote Erlang file server cannot be used. The computer
                    on which the Erlang node is running must have access to
                    the file system (directly or through NFS).

                binary:
                  Read operations on the file return binaries rather than
                  lists.

                {delayed_write, Size, Delay}:
                  Data in subsequent write/2 calls is buffered until at least
                  Size bytes are buffered, or until the oldest buffered data
                  is Delay milliseconds old. Then all buffered data is written
                  in one operating system call. The buffered data is also
                  flushed before some other file operation than write/2 is
                  executed.

                  The purpose of this option is to increase performance by
                  reducing the number of operating system calls. Thus, the
                  write/2 calls must be for sizes significantly less than
                  Size, and not interspersed by too many other file
                  operations.

                  When this option is used, the result of write/2 calls can
                  prematurely be reported as successful, and if a write error
                  occurs, the error is reported as the result of the next file
                  operation, which is not executed.

                  For example, when delayed_write is used, after a number of
                  write/2 calls, close/1 can return {error, enospc}, as there
                  is not enough space on the disc for previously written data.
                  close/1 must probably be called again, as the file is still
                  open.

                delayed_write:
                  The same as {delayed_write, Size, Delay} with reasonable
                  default values for Size and Delay (roughly some 64 KB, 2
                  seconds).

                {read_ahead, Size}:
                  Activates read data buffering. If read/2 calls are for
                  significantly less than Size bytes, read operations to the
                  operating system are still performed for blocks of Size
                  bytes. The extra data is buffered and returned in subsequent
                  read/2 calls, giving a performance gain as the number of
                  operating system calls is reduced.

                  The read_ahead buffer is also highly used by function
                  read_line/1 in raw mode, therefore this option is
                  recommended (for performance reasons) when accessing raw
                  files using that function.

                  If read/2 calls are for sizes not significantly less than,
                  or even greater than Size bytes, no performance gain can be
                  expected.

                read_ahead:
                  The same as {read_ahead, Size} with a reasonable default
                  value for Size (roughly some 64 KB).

                compressed:
                  Makes it possible to read or write gzip compressed files.
                  Option compressed must be combined with read or write, but
                  not both. Notice that the file size obtained with
                  read_file_info/1 does probably not match the number of bytes
                  that can be read from a compressed file.

                {encoding, Encoding}:
                  Makes the file perform automatic translation of characters
                  to and from a specific (Unicode) encoding. Notice that the
                  data supplied to write/2 or returned by read/2 still is
                  byte-oriented; this option denotes only how data is stored
                  in the disk file.

                  Depending on the encoding, different methods of reading and
                  writing data is preferred. The default encoding of latin1
                  implies using this module (file) for reading and writing
                  data as the interfaces provided here work with byte-oriented
                  data. Using other (Unicode) encodings makes the io(3)
                  functions get_chars, get_line, and put_chars more suitable,
                  as they can work with the full Unicode range.

                  If data is sent to an io_device() in a format that cannot be
                  converted to the specified encoding, or if data is read by a
                  function that returns data in a format that cannot cope with
                  the character range of the data, an error occurs and the
                  file is closed.

                  Allowed values for Encoding:

                  latin1:
                    The default encoding. Bytes supplied to the file, that is,
                    write/2 are written "as is" on the file. Likewise, bytes
                    read from the file, that is, read/2 are returned "as is".
                    If module io(3) is used for writing, the file can only
                    cope with Unicode characters up to code point 255 (the ISO
                    Latin-1 range).

                  unicode or utf8:
                    Characters are translated to and from UTF-8 encoding
                    before they are written to or read from the file. A file
                    opened in this way can be readable using function read/2,
                    as long as no data stored on the file lies beyond the ISO
                    Latin-1 range (0..255), but failure occurs if the data
                    contains Unicode code points beyond that range. The file
                    is best read with the functions in the Unicode aware
                    module io(3).

                    Bytes written to the file by any means are translated to
                    UTF-8 encoding before being stored on the disk file.

                  utf16 or {utf16,big}:
                    Works like unicode, but translation is done to and from
                    big endian UTF-16 instead of UTF-8.

                  {utf16,little}:
                    Works like unicode, but translation is done to and from
                    little endian UTF-16 instead of UTF-8.

                  utf32 or {utf32,big}:
                    Works like unicode, but translation is done to and from
                    big endian UTF-32 instead of UTF-8.

                  {utf32,little}:
                    Works like unicode, but translation is done to and from
                    little endian UTF-32 instead of UTF-8.

                  The Encoding can be changed for a file "on the fly" by using
                  function io:setopts/2. So a file can be analyzed in latin1
                  encoding for, for example, a BOM, positioned beyond the BOM
                  and then be set for the right encoding before further
                  reading. For functions identifying BOMs, see module
                  unicode(3).

                  This option is not allowed on raw files.

                ram:
                  File must be iodata(). Returns an fd(), which lets module
                  file operate on the data in-memory as if it is a file.

                sync:
                  On platforms supporting it, enables the POSIX O_SYNC
                  synchronous I/O flag or its platform-dependent equivalent
                  (for example, FILE_FLAG_WRITE_THROUGH on Windows) so that
                  writes to the file block until the data is physically
                  written to disk. However, be aware that the exact semantics
                  of this flag differ from platform to platform. For example,
                  none of Linux or Windows guarantees that all file metadata
                  are also written before the call returns. For precise
                  semantics, check the details of your platform documentation.
                  On platforms with no support for POSIX O_SYNC or equivalent,
                  use of the sync flag causes open to return {error, enotsup}.

              Returns:

                {ok, IoDevice}:
                  The file is opened in the requested mode. IoDevice is a
                  reference to the file.

                {error, Reason}:
                  The file cannot be opened.

              IoDevice is really the pid of the process that handles the file.
              This process is linked to the process that originally opened the
              file. If any process to which the IoDevice is linked terminates,
              the file is closed and the process itself is terminated. An
              IoDevice returned from this call can be used as an argument to
              the I/O functions (see io(3)).

          Note:
              In previous versions of file, modes were specified as one of the
              atoms read, write, or read_write instead of a list. This is
              still allowed for reasons of backwards compatibility, but is not
              to be used for new code. Also note that read_write is not
              allowed in a mode list.


              Typical error reasons:

                enoent:
                  The file does not exist.

                eacces:
                  Missing permission for reading the file or searching one of
                  the parent directories.

                eisdir:
                  The named file is a directory.

                enotdir:
                  A component of the filename is not a directory. On some
                  platforms, enoent is returned instead.

                enospc:
                  There is no space left on the device (if write access was
                  specified).

       path_consult(Path, Filename) ->
                       {ok, Terms, FullName} | {error, Reason}

              Types:

                 Path = [Dir]
                 Dir = Filename = name_all()
                 Terms = [term()]
                 FullName = filename_all()
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              Searches the path Path (a list of directory names) until the
              file Filename is found. If Filename is an absolute filename,
              Path is ignored. Then reads Erlang terms, separated by '.', from
              the file.

              Returns one of the following:

                {ok, Terms, FullName}:
                  The file is successfully read. FullName is the full name of
                  the file.

                {error, enoent}:
                  The file cannot be found in any of the directories in Path.

                {error, atom()}:
                  An error occurred when opening the file or reading it. For a
                  list of typical error codes, see open/2.

                {error, {Line, Mod, Term}}:
                  An error occurred when interpreting the Erlang terms in the
                  file. Use format_error/1 to convert the three-element tuple
                  to an English description of the error.

              The encoding of Filename can be set by a comment as described in
              epp(3).

       path_eval(Path, Filename) -> {ok, FullName} | {error, Reason}

              Types:

                 Path = [Dir :: name_all()]
                 Filename = name_all()
                 FullName = filename_all()
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              Searches the path Path (a list of directory names) until the
              file Filename is found. If Filename is an absolute filename,
              Path is ignored. Then reads and evaluates Erlang expressions,
              separated by '.' (or ',', a sequence of expressions is also an
              expression), from the file. The result of evaluation is not
              returned; any expression sequence in the file must be there for
              its side effect.

              Returns one of the following:

                {ok, FullName}:
                  The file is read and evaluated. FullName is the full name of
                  the file.

                {error, enoent}:
                  The file cannot be found in any of the directories in Path.

                {error, atom()}:
                  An error occurred when opening the file or reading it. For a
                  list of typical error codes, see open/2.

                {error, {Line, Mod, Term}}:
                  An error occurred when interpreting the Erlang expressions
                  in the file. Use format_error/1 to convert the three-element
                  tuple to an English description of the error.

              The encoding of Filename can be set by a comment as described in
              epp(3).

       path_open(Path, Filename, Modes) ->
                    {ok, IoDevice, FullName} | {error, Reason}

              Types:

                 Path = [Dir :: name_all()]
                 Filename = name_all()
                 Modes = [mode()]
                 IoDevice = io_device()
                 FullName = filename_all()
                 Reason = posix() | badarg | system_limit

              Searches the path Path (a list of directory names) until the
              file Filename is found. If Filename is an absolute filename,
              Path is ignored. Then opens the file in the mode determined by
              Modes.

              Returns one of the following:

                {ok, IoDevice, FullName}:
                  The file is opened in the requested mode. IoDevice is a
                  reference to the file and FullName is the full name of the
                  file.

                {error, enoent}:
                  The file cannot be found in any of the directories in Path.

                {error, atom()}:
                  The file cannot be opened.

       path_script(Path, Filename) ->
                      {ok, Value, FullName} | {error, Reason}

              Types:

                 Path = [Dir :: name_all()]
                 Filename = name_all()
                 Value = term()
                 FullName = filename_all()
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              Searches the path Path (a list of directory names) until the
              file Filename is found. If Filename is an absolute filename,
              Path is ignored. Then reads and evaluates Erlang expressions,
              separated by '.' (or ',', a sequence of expressions is also an
              expression), from the file.

              Returns one of the following:

                {ok, Value, FullName}:
                  The file is read and evaluated. FullName is the full name of
                  the file and Value the value of the last expression.

                {error, enoent}:
                  The file cannot be found in any of the directories in Path.

                {error, atom()}:
                  An error occurred when opening the file or reading it. For a
                  list of typical error codes, see open/2.

                {error, {Line, Mod, Term}}:
                  An error occurred when interpreting the Erlang expressions
                  in the file. Use format_error/1 to convert the three-element
                  tuple to an English description of the error.

              The encoding of Filename can be set by a comment as described in
              epp(3).

       path_script(Path, Filename, Bindings) ->
                      {ok, Value, FullName} | {error, Reason}

              Types:

                 Path = [Dir :: name_all()]
                 Filename = name_all()
                 Bindings = erl_eval:binding_struct()
                 Value = term()
                 FullName = filename_all()
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              The same as path_script/2 but the variable bindings Bindings are
              used in the evaluation. See erl_eval(3) about variable bindings.

       pid2name(Pid) -> {ok, Filename} | undefined

              Types:

                 Filename = filename_all()
                 Pid = pid()

              If Pid is an I/O device, that is, a pid returned from open/2,
              this function returns the filename, or rather:

                {ok, Filename}:
                  If the file server of this node is not a slave, the file was
                  opened by the file server of this node (this implies that
                  Pid must be a local pid) and the file is not closed.
                  Filename is the filename in flat string format.

                undefined:
                  In all other cases.

          Warning:
              This function is intended for debugging only.


       position(IoDevice, Location) ->
                   {ok, NewPosition} | {error, Reason}

              Types:

                 IoDevice = io_device()
                 Location = location()
                 NewPosition = integer()
                 Reason = posix() | badarg | terminated

              Sets the position of the file referenced by IoDevice to
              Location. Returns {ok, NewPosition} (as absolute offset) if
              successful, otherwise {error, Reason}. Location is one of the
              following:

                Offset:
                  The same as {bof, Offset}.

                {bof, Offset}:
                  Absolute offset.

                {cur, Offset}:
                  Offset from the current position.

                {eof, Offset}:
                  Offset from the end of file.

                bof | cur | eof:
                  The same as above with Offset 0.

              Notice that offsets are counted in bytes, not in characters. If
              the file is opened using some other encoding than latin1, one
              byte does not correspond to one character. Positioning in such a
              file can only be done to known character boundaries. That is, to
              a position earlier retrieved by getting a current position, to
              the beginning/end of the file or to some other position known to
              be on a correct character boundary by some other means
              (typically beyond a byte order mark in the file, which has a
              known byte-size).

              A typical error reason is:

                einval:
                  Either Location is illegal, or it is evaluated to a negative
                  offset in the file. Notice that if the resulting position is
                  a negative value, the result is an error, and after the call
                  the file position is undefined.

       pread(IoDevice, LocNums) -> {ok, DataL} | eof | {error, Reason}

              Types:

                 IoDevice = io_device()
                 LocNums =
                     [{Location :: location(), Number :: integer() >= 0}]
                 DataL = [Data]
                 Data = string() | binary() | eof
                 Reason = posix() | badarg | terminated

              Performs a sequence of pread/3 in one operation, which is more
              efficient than calling them one at a time. Returns {ok, [Data,
              ...]} or {error, Reason}, where each Data, the result of the
              corresponding pread, is either a list or a binary depending on
              the mode of the file, or eof if the requested position is beyond
              end of file.

              As the position is specified as a byte-offset, take special
              caution when working with files where encoding is set to
              something else than latin1, as not every byte position is a
              valid character boundary on such a file.

       pread(IoDevice, Location, Number) ->
                {ok, Data} | eof | {error, Reason}

              Types:

                 IoDevice = io_device()
                 Location = location()
                 Number = integer() >= 0
                 Data = string() | binary()
                 Reason = posix() | badarg | terminated

              Combines position/2 and read/2 in one operation, which is more
              efficient than calling them one at a time. If IoDevice is opened
              in raw mode, some restrictions apply:

                * Location is only allowed to be an integer.

                * The current position of the file is undefined after the
                  operation.

              As the position is specified as a byte-offset, take special
              caution when working with files where encoding is set to
              something else than latin1, as not every byte position is a
              valid character boundary on such a file.

       pwrite(IoDevice, LocBytes) -> ok | {error, {N, Reason}}

              Types:

                 IoDevice = io_device()
                 LocBytes = [{Location :: location(), Bytes :: iodata()}]
                 N = integer() >= 0
                 Reason = posix() | badarg | terminated

              Performs a sequence of pwrite/3 in one operation, which is more
              efficient than calling them one at a time. Returns ok or {error,
              {N, Reason}}, where N is the number of successful writes done
              before the failure.

              When positioning in a file with other encoding than latin1,
              caution must be taken to set the position on a correct character
              boundary. For details, see position/2.

       pwrite(IoDevice, Location, Bytes) -> ok | {error, Reason}

              Types:

                 IoDevice = io_device()
                 Location = location()
                 Bytes = iodata()
                 Reason = posix() | badarg | terminated

              Combines position/2 and write/2 in one operation, which is more
              efficient than calling them one at a time. If IoDevice has been
              opened in raw mode, some restrictions apply:

                * Location is only allowed to be an integer.

                * The current position of the file is undefined after the
                  operation.

              When positioning in a file with other encoding than latin1,
              caution must be taken to set the position on a correct character
              boundary. For details, see position/2.

       read(IoDevice, Number) -> {ok, Data} | eof | {error, Reason}

              Types:

                 IoDevice = io_device() | atom()
                 Number = integer() >= 0
                 Data = string() | binary()
                 Reason =
                     posix() |
                     badarg | terminated |
                     {no_translation, unicode, latin1}

              Reads Number bytes/characters from the file referenced by
              IoDevice. The functions read/2, pread/3, and read_line/1 are the
              only ways to read from a file opened in raw mode (although they
              work for normally opened files, too).

              For files where encoding is set to something else than latin1,
              one character can be represented by more than one byte on the
              file. The parameter Number always denotes the number of
              characters read from the file, while the position in the file
              can be moved much more than this number when reading a Unicode
              file.

              Also, if encoding is set to something else than latin1, the
              read/3 call fails if the data contains characters larger than
              255, which is why module io(3) is to be preferred when reading
              such a file.

              The function returns:

                {ok, Data}:
                  If the file was opened in binary mode, the read bytes are
                  returned in a binary, otherwise in a list. The list or
                  binary is shorter than the number of bytes requested if end
                  of file was reached.

                eof:
                  Returned if Number>0 and end of file was reached before
                  anything at all could be read.

                {error, Reason}:
                  An error occurred.

              Typical error reasons:

                ebadf:
                  The file is not opened for reading.

                {no_translation, unicode, latin1}:
                  The file is opened with another encoding than latin1 and the
                  data in the file cannot be translated to the byte-oriented
                  data that this function returns.

       read_file(Filename) -> {ok, Binary} | {error, Reason}

              Types:

                 Filename = name_all()
                 Binary = binary()
                 Reason = posix() | badarg | terminated | system_limit

              Returns {ok, Binary}, where Binary is a binary data object that
              contains the contents of Filename, or {error, Reason} if an
              error occurs.

              Typical error reasons:

                enoent:
                  The file does not exist.

                eacces:
                  Missing permission for reading the file, or for searching
                  one of the parent directories.

                eisdir:
                  The named file is a directory.

                enotdir:
                  A component of the filename is not a directory. On some
                  platforms, enoent is returned instead.

                enomem:
                  There is not enough memory for the contents of the file.

       read_file_info(Filename) -> {ok, FileInfo} | {error, Reason}

       read_file_info(Filename, Opts) -> {ok, FileInfo} | {error, Reason}

              Types:

                 Filename = name_all()
                 Opts = [file_info_option()]
                 FileInfo = file_info()
                 Reason = posix() | badarg

              Retrieves information about a file. Returns {ok, FileInfo} if
              successful, otherwise {error, Reason}. FileInfo is a record
              file_info, defined in the Kernel include file file.hrl. Include
              the following directive in the module from which the function is
              called:

               -include_lib("kernel/include/file.hrl").

              The time type returned in atime, mtime, and ctime is dependent
              on the time type set in Opts :: {time, Type} as follows:

                local:
                  Returns local time.

                universal:
                  Returns universal time.

                posix:
                  Returns seconds since or before Unix time epoch, which is
                  1970-01-01 00:00 UTC.

              Default is {time, local}.

              If the option raw is set, the file server is not called and only
              information about local files is returned. Note that this will
              break this module's atomicity guarantees as it can race with a
              concurrent call to write_file_info/1,2

          Note:
              As file times are stored in POSIX time on most OS, it is faster
              to query file information with option posix.


              The record file_info contains the following fields:

                size = integer() >= 0:
                  Size of file in bytes.

                type = device | directory | other | regular | symlink:
                  The type of the file.

                access = read | write | read_write | none:
                  The current system access to the file.

                atime = date_time() | integer() >= 0:
                  The last time the file was read.

                mtime = date_time() | integer() >= 0:
                  The last time the file was written.

                ctime = date_time() | integer() >=0:
                  The interpretation of this time field depends on the
                  operating system. On Unix, it is the last time the file or
                  the inode was changed. In Windows, it is the create time.

                mode = integer() >= 0:
                  The file permissions as the sum of the following bit values:

                  8#00400:
                    read permission: owner

                  8#00200:
                    write permission: owner

                  8#00100:
                    execute permission: owner

                  8#00040:
                    read permission: group

                  8#00020:
                    write permission: group

                  8#00010:
                    execute permission: group

                  8#00004:
                    read permission: other

                  8#00002:
                    write permission: other

                  8#00001:
                    execute permission: other

                  16#800:
                    set user id on execution

                  16#400:
                    set group id on execution

                  On Unix platforms, other bits than those listed above may be
                  set.

                links = integer() >= 0:
                  Number of links to the file (this is always 1 for file
                  systems that have no concept of links).

                major_device = integer() >= 0:
                  Identifies the file system where the file is located. In
                  Windows, the number indicates a drive as follows: 0 means
                  A:, 1 means B:, and so on.

                minor_device = integer() >= 0:
                  Only valid for character devices on Unix. In all other
                  cases, this field is zero.

                inode = integer() >= 0:
                  Gives the inode number. On non-Unix file systems, this field
                  is zero.

                uid = integer() >= 0:
                  Indicates the owner of the file. On non-Unix file systems,
                  this field is zero.

                gid = integer() >= 0:
                  Gives the group that the owner of the file belongs to. On
                  non-Unix file systems, this field is zero.

              Typical error reasons:

                eacces:
                  Missing search permission for one of the parent directories
                  of the file.

                enoent:
                  The file does not exist.

                enotdir:
                  A component of the filename is not a directory. On some
                  platforms, enoent is returned instead.

       read_line(IoDevice) -> {ok, Data} | eof | {error, Reason}

              Types:

                 IoDevice = io_device() | atom()
                 Data = string() | binary()
                 Reason =
                     posix() |
                     badarg | terminated |
                     {no_translation, unicode, latin1}

              Reads a line of bytes/characters from the file referenced by
              IoDevice. Lines are defined to be delimited by the linefeed (LF,
              \n) character, but any carriage return (CR, \r) followed by a
              newline is also treated as a single LF character (the carriage
              return is silently ignored). The line is returned including the
              LF, but excluding any CR immediately followed by an LF. This
              behaviour is consistent with the behaviour of io:get_line/2. If
              end of file is reached without any LF ending the last line, a
              line with no trailing LF is returned.

              The function can be used on files opened in raw mode. However,
              it is inefficient to use it on raw files if the file is not
              opened with option {read_ahead, Size} specified. Thus, combining
              raw and {read_ahead, Size} is highly recommended when opening a
              text file for raw line-oriented reading.

              If encoding is set to something else than latin1, the
              read_line/1 call fails if the data contains characters larger
              than 255, why module io(3) is to be preferred when reading such
              a file.

              The function returns:

                {ok, Data}:
                  One line from the file is returned, including the trailing
                  LF, but with CRLF sequences replaced by a single LF (see
                  above).

                  If the file is opened in binary mode, the read bytes are
                  returned in a binary, otherwise in a list.

                eof:
                  Returned if end of file was reached before anything at all
                  could be read.

                {error, Reason}:
                  An error occurred.

              Typical error reasons:

                ebadf:
                  The file is not opened for reading.

                {no_translation, unicode, latin1}:
                  The file is opened with another encoding than latin1 and the
                  data on the file cannot be translated to the byte-oriented
                  data that this function returns.

       read_link(Name) -> {ok, Filename} | {error, Reason}

              Types:

                 Name = name_all()
                 Filename = filename()
                 Reason = posix() | badarg

              Returns {ok, Filename} if Name refers to a symbolic link that is
              not a raw filename, or {error, Reason} otherwise. On platforms
              that do not support symbolic links, the return value is
              {error,enotsup}.

              Typical error reasons:

                einval:
                  Name does not refer to a symbolic link or the name of the
                  file that it refers to does not conform to the expected
                  encoding.

                enoent:
                  The file does not exist.

                enotsup:
                  Symbolic links are not supported on this platform.

       read_link_all(Name) -> {ok, Filename} | {error, Reason}

              Types:

                 Name = name_all()
                 Filename = filename_all()
                 Reason = posix() | badarg

              Returns {ok, Filename} if Name refers to a symbolic link or
              {error, Reason} otherwise. On platforms that do not support
              symbolic links, the return value is {error,enotsup}.

              Notice that Filename can be either a list or a binary.

              Typical error reasons:

                einval:
                  Name does not refer to a symbolic link.

                enoent:
                  The file does not exist.

                enotsup:
                  Symbolic links are not supported on this platform.

       read_link_info(Name) -> {ok, FileInfo} | {error, Reason}

       read_link_info(Name, Opts) -> {ok, FileInfo} | {error, Reason}

              Types:

                 Name = name_all()
                 Opts = [file_info_option()]
                 FileInfo = file_info()
                 Reason = posix() | badarg

              Works like read_file_info/1,2 except that if Name is a symbolic
              link, information about the link is returned in the file_info
              record and the type field of the record is set to symlink.

              If the option raw is set, the file server is not called and only
              information about local files is returned. Note that this will
              break this module's atomicity guarantees as it can race with a
              concurrent call to write_file_info/1,2

              If Name is not a symbolic link, this function returns the same
              result as read_file_info/1. On platforms that do not support
              symbolic links, this function is always equivalent to
              read_file_info/1.

       rename(Source, Destination) -> ok | {error, Reason}

              Types:

                 Source = Destination = name_all()
                 Reason = posix() | badarg

              Tries to rename the file Source to Destination. It can be used
              to move files (and directories) between directories, but it is
              not sufficient to specify the destination only. The destination
              filename must also be specified. For example, if bar is a normal
              file and foo and baz are directories, rename("foo/bar", "baz")
              returns an error, but rename("foo/bar", "baz/bar") succeeds.
              Returns ok if it is successful.

          Note:
              Renaming of open files is not allowed on most platforms (see
              eacces below).


              Typical error reasons:

                eacces:
                  Missing read or write permissions for the parent directories
                  of Source or Destination. On some platforms, this error is
                  given if either Source or Destination is open.

                eexist:
                  Destination is not an empty directory. On some platforms,
                  also given when Source and Destination are not of the same
                  type.

                einval:
                  Source is a root directory, or Destination is a subdirectory
                  of Source.

                eisdir:
                  Destination is a directory, but Source is not.

                enoent:
                  Source does not exist.

                enotdir:
                  Source is a directory, but Destination is not.

                exdev:
                  Source and Destination are on different file systems.

       script(Filename) -> {ok, Value} | {error, Reason}

              Types:

                 Filename = name_all()
                 Value = term()
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              Reads and evaluates Erlang expressions, separated by '.' (or
              ',', a sequence of expressions is also an expression), from the
              file.

              Returns one of the following:

                {ok, Value}:
                  The file is read and evaluated. Value is the value of the
                  last expression.

                {error, atom()}:
                  An error occurred when opening the file or reading it. For a
                  list of typical error codes, see open/2.

                {error, {Line, Mod, Term}}:
                  An error occurred when interpreting the Erlang expressions
                  in the file. Use format_error/1 to convert the three-element
                  tuple to an English description of the error.

              The encoding of Filename can be set by a comment as described in
              epp(3).

       script(Filename, Bindings) -> {ok, Value} | {error, Reason}

              Types:

                 Filename = name_all()
                 Bindings = erl_eval:binding_struct()
                 Value = term()
                 Reason =
                     posix() |
                     badarg | terminated | system_limit |
                     {Line :: integer(), Mod :: module(), Term :: term()}

              The same as script/1 but the variable bindings Bindings are used
              in the evaluation. See erl_eval(3) about variable bindings.

       sendfile(Filename, Socket) ->
                   {ok, integer() >= 0} |
                   {error, inet:posix() | closed | badarg | not_owner}

              Types:

                 Filename = name_all()
                 Socket = inet:socket()

              Sends the file Filename to Socket. Returns {ok, BytesSent} if
              successful, otherwise {error, Reason}.

       sendfile(RawFile, Socket, Offset, Bytes, Opts) ->
                   {ok, integer() >= 0} |
                   {error, inet:posix() | closed | badarg | not_owner}

              Types:

                 RawFile = fd()
                 Socket = inet:socket()
                 Offset = Bytes = integer() >= 0
                 Opts = [sendfile_option()]
                 sendfile_option() =
                     {chunk_size, integer() >= 0} | {use_threads, boolean()}

              Sends Bytes from the file referenced by RawFile beginning at
              Offset to Socket. Returns {ok, BytesSent} if successful,
              otherwise {error, Reason}. If Bytes is set to 0 all data after
              the specified Offset is sent.

              The file used must be opened using the raw flag, and the process
              calling sendfile must be the controlling process of the socket.
              See gen_tcp:controlling_process/2.

              If the OS used does not support non-blocking sendfile, an Erlang
              fallback using read/2 and gen_tcp:send/2 is used.

              The option list can contain the following options:

                chunk_size:
                  The chunk size used by the Erlang fallback to send data. If
                  using the fallback, set this to a value that comfortably
                  fits in the systems memory. Default is 20 MB.

       set_cwd(Dir) -> ok | {error, Reason}

              Types:

                 Dir = name() | EncodedBinary
                 EncodedBinary = binary()
                 Reason = posix() | badarg | no_translation

              Sets the current working directory of the file server to Dir.
              Returns ok if successful.

              The functions in the module file usually treat binaries as raw
              filenames, that is, they are passed "as is" even when the
              encoding of the binary does not agree with
              native_name_encoding(). However, this function expects binaries
              to be encoded according to the value returned by
              native_name_encoding().

              Typical error reasons are:

                enoent:
                  The directory does not exist.

                enotdir:
                  A component of Dir is not a directory. On some platforms,
                  enoent is returned.

                eacces:
                  Missing permission for the directory or one of its parents.

                badarg:
                  Dir has an improper type, such as tuple.

                no_translation:
                  Dir is a binary() with characters coded in ISO-latin-1 and
                  the VM is operating with unicode filename encoding.

          Warning:
              In a future release, a bad type for argument Dir will probably
              generate an exception.


       sync(IoDevice) -> ok | {error, Reason}

              Types:

                 IoDevice = io_device()
                 Reason = posix() | badarg | terminated

              Ensures that any buffers kept by the operating system (not by
              the Erlang runtime system) are written to disk. On some
              platforms, this function might have no effect.

              A typical error reason is:

                enospc:
                  Not enough space left to write the file.

       truncate(IoDevice) -> ok | {error, Reason}

              Types:

                 IoDevice = io_device()
                 Reason = posix() | badarg | terminated

              Truncates the file referenced by IoDevice at the current
              position. Returns ok if successful, otherwise {error, Reason}.

       write(IoDevice, Bytes) -> ok | {error, Reason}

              Types:

                 IoDevice = io_device() | atom()
                 Bytes = iodata()
                 Reason = posix() | badarg | terminated

              Writes Bytes to the file referenced by IoDevice. This function
              is the only way to write to a file opened in raw mode (although
              it works for normally opened files too). Returns ok if
              successful, and {error, Reason} otherwise.

              If the file is opened with encoding set to something else than
              latin1, each byte written can result in many bytes being written
              to the file, as the byte range 0..255 can represent anything
              between one and four bytes depending on value and UTF encoding
              type.

              Typical error reasons:

                ebadf:
                  The file is not opened for writing.

                enospc:
                  No space is left on the device.

       write_file(Filename, Bytes) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Bytes = iodata()
                 Reason = posix() | badarg | terminated | system_limit

              Writes the contents of the iodata term Bytes to file Filename.
              The file is created if it does not exist. If it exists, the
              previous contents are overwritten. Returns ok if successful,
              otherwise {error, Reason}.

              Typical error reasons:

                enoent:
                  A component of the filename does not exist.

                enotdir:
                  A component of the filename is not a directory. On some
                  platforms, enoent is returned instead.

                enospc:
                  No space is left on the device.

                eacces:
                  Missing permission for writing the file or searching one of
                  the parent directories.

                eisdir:
                  The named file is a directory.

       write_file(Filename, Bytes, Modes) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Bytes = iodata()
                 Modes = [mode()]
                 Reason = posix() | badarg | terminated | system_limit

              Same as write_file/2, but takes a third argument Modes, a list
              of possible modes, see open/2. The mode flags binary and write
              are implicit, so they are not to be used.

       write_file_info(Filename, FileInfo) -> ok | {error, Reason}

       write_file_info(Filename, FileInfo, Opts) -> ok | {error, Reason}

              Types:

                 Filename = name_all()
                 Opts = [file_info_option()]
                 FileInfo = file_info()
                 Reason = posix() | badarg

              Changes file information. Returns ok if successful, otherwise
              {error, Reason}. FileInfo is a record file_info, defined in the
              Kernel include file file.hrl. Include the following directive in
              the module from which the function is called:

               -include_lib("kernel/include/file.hrl").

              The time type set in atime, mtime, and ctime depends on the time
              type set in Opts :: {time, Type} as follows:

                local:
                  Interprets the time set as local.

                universal:
                  Interprets it as universal time.

                posix:
                  Must be seconds since or before Unix time epoch, which is
                  1970-01-01 00:00 UTC.

              Default is {time, local}.

              If the option raw is set, the file server is not called and only
              information about local files is returned.

              The following fields are used from the record, if they are
              specified:

                atime = date_time() | integer() >= 0:
                  The last time the file was read.

                mtime = date_time() | integer() >= 0:
                  The last time the file was written.

                ctime = date_time() | integer() >= 0:
                  On Unix, any value specified for this field is ignored (the
                  "ctime" for the file is set to the current time). On
                  Windows, this field is the new creation time to set for the
                  file.

                mode = integer() >= 0:
                  The file permissions as the sum of the following bit values:

                  8#00400:
                    Read permission: owner

                  8#00200:
                    Write permission: owner

                  8#00100:
                    Execute permission: owner

                  8#00040:
                    Read permission: group

                  8#00020:
                    Write permission: group

                  8#00010:
                    Execute permission: group

                  8#00004:
                    Read permission: other

                  8#00002:
                    Write permission: other

                  8#00001:
                    Execute permission: other

                  16#800:
                    Set user id on execution

                  16#400:
                    Set group id on execution

                  On Unix platforms, other bits than those listed above may be
                  set.

                uid = integer() >= 0:
                  Indicates the file owner. Ignored for non-Unix file systems.

                gid = integer() >= 0:
                  Gives the group that the file owner belongs to. Ignored for
                  non-Unix file systems.

              Typical error reasons:

                eacces:
                  Missing search permission for one of the parent directories
                  of the file.

                enoent:
                  The file does not exist.

                enotdir:
                  A component of the filename is not a directory. On some
                  platforms, enoent is returned instead.

POSIX ERROR CODES
         * eacces - Permission denied

         * eagain - Resource temporarily unavailable

         * ebadf - Bad file number

         * ebusy - File busy

         * edquot - Disk quota exceeded

         * eexist - File already exists

         * efault - Bad address in system call argument

         * efbig - File too large

         * eintr - Interrupted system call

         * einval - Invalid argument

         * eio - I/O error

         * eisdir - Illegal operation on a directory

         * eloop - Too many levels of symbolic links

         * emfile - Too many open files

         * emlink - Too many links

         * enametoolong - Filename too long

         * enfile - File table overflow

         * enodev - No such device

         * enoent - No such file or directory

         * enomem - Not enough memory

         * enospc - No space left on device

         * enotblk - Block device required

         * enotdir - Not a directory

         * enotsup - Operation not supported

         * enxio - No such device or address

         * eperm - Not owner

         * epipe - Broken pipe

         * erofs - Read-only file system

         * espipe - Invalid seek

         * esrch - No such process

         * estale - Stale remote file handle

         * exdev - Cross-domain link

PERFORMANCE
       For increased performance, raw files are recommended.

       A normal file is really a process so it can be used as an I/O device
       (see io). Therefore, when data is written to a normal file, the sending
       of the data to the file process, copies all data that are not binaries.
       Opening the file in binary mode and writing binaries is therefore
       recommended. If the file is opened on another node, or if the file
       server runs as slave to the file server of another node, also binaries
       are copied.

   Note:
       Raw files use the file system of the host machine of the node. For
       normal files (non-raw), the file server is used to find the files, and
       if the node is running its file server as slave to the file server of
       another node, and the other node runs on some other host machine, they
       can have different file systems. However, this is seldom a problem.


       open/2 can be given the options delayed_write and read_ahead to turn on
       caching, which will reduce the number of operating system calls and
       greatly improve performance for small reads and writes. However, the
       overhead won't disappear completely and it's best to keep the number of
       file operations to a minimum. As a contrived example, the following
       function writes 4MB in 2.5 seconds when tested:

       create_file_slow(Name) ->
           {ok, Fd} = file:open(Name, [raw, write, delayed_write, binary]),
           create_file_slow_1(Fd, 4 bsl 20),
           file:close(Fd).

       create_file_slow_1(_Fd, 0) ->
           ok;
       create_file_slow_1(Fd, M) ->
           ok = file:write(Fd, <<0>>),
           create_file_slow_1(Fd, M - 1).

       The following functionally equivalent code writes 128 bytes per call to
       write/2 and so does the same work in 0.08 seconds, which is roughly 30
       times faster:

       create_file(Name) ->
           {ok, Fd} = file:open(Name, [raw, write, delayed_write, binary]),
           create_file_1(Fd, 4 bsl 20),
           file:close(Fd),
           ok.

       create_file_1(_Fd, 0) ->
           ok;
       create_file_1(Fd, M) when M >= 128 ->
           ok = file:write(Fd, <<0:(128)/unit:8>>),
           create_file_1(Fd, M - 128);
       create_file_1(Fd, M) ->
           ok = file:write(Fd, <<0:(M)/unit:8>>),
           create_file_1(Fd, M - 1).

       When writing data it's generally more efficient to write a list of
       binaries rather than a list of integers. It is not needed to flatten a
       deep list before writing. On Unix hosts, scatter output, which writes a
       set of buffers in one operation, is used when possible. In this way
       write(FD, [Bin1, Bin2 | Bin3]) writes the contents of the binaries
       without copying the data at all, except for perhaps deep down in the
       operating system kernel.

   Warning:
       If an error occurs when accessing an open file with module io, the
       process handling the file exits. The dead file process can hang if a
       process tries to access it later. This will be fixed in a future
       release.


SEE ALSO
       filename(3)



Ericsson AB                      kernel 6.5.1                          file(3)