Elixir v1.4.5 File View Source
This module contains functions to manipulate files.
Some of those functions are low-level, allowing the user
to interact with files or IO devices, like open/2
,
copy/3
and others. This module also provides higher
level functions that work with filenames and have their naming
based on UNIX variants. For example, one can copy a file
via cp/3
and remove files and directories recursively
via rm_rf/1
.
Encoding
In order to write and read files, one must use the functions
in the IO
module. By default, a file is opened in binary mode,
which requires the functions IO.binread/2
and IO.binwrite/2
to interact with the file. A developer may pass :utf8
as an
option when opening the file, then the slower IO.read/2
and
IO.write/2
functions must be used as they are responsible for
doing the proper conversions and providing the proper data guarantees.
Note that filenames when given as charlists in Elixir are always treated as UTF-8. In particular, we expect that the shell and the operating system are configured to use UTF-8 encoding. Binary filenames are considered raw and passed to the OS as is.
API
Most of the functions in this module return :ok
or
{:ok, result}
in case of success, {:error, reason}
otherwise. Those functions also have a variant
that ends with !
which returns the result (instead of the
{:ok, result}
tuple) in case of success or raises an
exception in case it fails. For example:
File.read("hello.txt")
#=> {:ok, "World"}
File.read("invalid.txt")
#=> {:error, :enoent}
File.read!("hello.txt")
#=> "World"
File.read!("invalid.txt")
#=> raises File.Error
In general, a developer should use the former in case they want to react if the file does not exist. The latter should be used when the developer expects their software to fail in case the file cannot be read (i.e. it is literally an exception).
Processes and raw files
Every time a file is opened, Elixir spawns a new process. Writing to a file is equivalent to sending messages to the process that writes to the file descriptor.
This means files can be passed between nodes and message passing guarantees they can write to the same file in a network.
However, you may not always want to pay the price for this abstraction.
In such cases, a file can be opened in :raw
mode. The options :read_ahead
and :delayed_write
are also useful when operating on large files or
working with files in tight loops.
Check :file.open/2
for more information
about such options and other performance considerations.
Link to this section Summary
Functions
Sets the current working directory
Changes the current directory to the given path
,
executes the given function and then reverts back
to the previous path regardless of whether there is an exception
Changes the group given by the group id gid
for a given file
. Returns :ok
on success, or
{:error, reason}
on failure
Same as chgrp/2
, but raises an exception in case of failure. Otherwise :ok
Changes the mode
for a given file
Same as chmod/2
, but raises an exception in case of failure. Otherwise :ok
Changes the owner given by the user id uid
for a given file
. Returns :ok
on success,
or {:error, reason}
on failure
Same as chown/2
, but raises an exception in case of failure. Otherwise :ok
Closes the file referenced by io_device
. It mostly returns :ok
, except
for some severe errors such as out of memory
Copies the contents of source
to destination
The same as copy/3
but raises an File.CopyError
if it fails.
Returns the bytes_copied
otherwise
Copies the contents in source
to destination
preserving its mode
The same as cp/3
, but raises File.CopyError
if it fails.
Returns :ok
otherwise
Copies the contents in source to destination
The same as cp_r/3
, but raises File.CopyError
if it fails.
Returns the list of copied files otherwise
Gets the current working directory
Returns true
if the path is a directory
Returns true
if the given path exists.
It can be regular file, directory, socket,
symbolic link, named pipe or device file
Creates a symbolic link new
to the file or directory existing
Returns the list of files in the given directory
The same as ls/1
but raises File.Error
in case of an error
Same as lstat/2
but returns the File.Stat
struct directly and
throws File.Error
if an error is returned
Tries to create the directory path
. Missing parent directories are not created.
Returns :ok
if successful, or {:error, reason}
if an error occurs
Same as mkdir/1
, but raises an exception in case of failure. Otherwise :ok
Tries to create the directory path
. Missing parent directories are created.
Returns :ok
if successful, or {:error, reason}
if an error occurs
Same as mkdir_p/1
, but raises an exception in case of failure. Otherwise :ok
Opens the given path
Similar to open/2
but expects a function as its last argument
Similar to open/2
but raises an error if file could not be opened
Similar to open/3
but raises an error if file could not be opened
Returns {:ok, binary}
, where binary
is a binary data object that contains the contents
of path
, or {:error, reason}
if an error occurs
Returns a binary with the contents of the given filename or raises
File.Error
if an error occurs
Returns true
if the path is a regular file
Renames the source
file to destination
file. It can be used to move files
(and directories) between directories. If moving a file, you must fully
specify the destination
filename, it is not sufficient to simply specify
its directory
Tries to delete the file path
Removes files and directories recursively at the given path
.
Symlinks are not followed but simply removed, non-existing
files are simply ignored (i.e. doesn’t make this function fail)
Same as rm_rf/1
but raises File.Error
in case of failures,
otherwise the list of files or directories removed
Tries to delete the dir at path
.
Returns :ok
if successful, or {:error, reason}
if an error occurs
Same as rmdir/1
, but raises an exception in case of failure. Otherwise :ok
Same as stat/2
but returns the File.Stat
directly and
throws File.Error
if an error is returned
Returns a File.Stream
for the given path
with the given modes
Updates modification time (mtime) and access time (atime) of the given file
Same as touch/2
but raises an exception if it fails
Writes content
to the file path
Same as write/3
but raises an exception if it fails, returns :ok
otherwise
Writes the given File.Stat
back to the filesystem at the given
path. Returns :ok
or {:error, reason}
Same as write_stat/3
but raises an exception if it fails.
Returns :ok
otherwise
Link to this section Types
mode :: :append | :binary | :charlist | :compressed | :delayed_write | :exclusive | :raw | :read | :read_ahead | :sync | :utf8 | :write | {:encoding, :latin1 | :unicode | :utf8 | :utf16 | :utf32 | {:utf16, :big | :little} | {:utf32, :big | :little}} | {:read_ahead, pos_integer} | {:delayed_write, non_neg_integer, non_neg_integer}
stat_options() :: [{:time, :local | :universal | :posix}]
Link to this section Functions
Sets the current working directory.
Returns :ok
if successful, {:error, reason}
otherwise.
The same as cd/1
, but raises an exception if it fails.
cd!(Path.t, (() -> res)) :: res | no_return when res: var
Changes the current directory to the given path
,
executes the given function and then reverts back
to the previous path regardless of whether there is an exception.
Raises an error if retrieving or changing the current directory fails.
Changes the group given by the group id gid
for a given file
. Returns :ok
on success, or
{:error, reason}
on failure.
chgrp!(Path.t, non_neg_integer) :: :ok | no_return
Same as chgrp/2
, but raises an exception in case of failure. Otherwise :ok
.
Changes the mode
for a given file
.
Returns :ok
on success, or {:error, reason}
on failure.
Permissions
0o400 - read permission: owner
0o200 - write permission: owner
0o100 - execute permission: owner
0o040 - read permission: group
0o020 - write permission: group
0o010 - execute permission: group
0o004 - read permission: other
0o002 - write permission: other
0o001 - execute permission: other
For example, setting the mode 0o755 gives it write, read and execute permission to the owner and both read and execute permission to group and others.
chmod!(Path.t, non_neg_integer) :: :ok | no_return
Same as chmod/2
, but raises an exception in case of failure. Otherwise :ok
.
Changes the owner given by the user id uid
for a given file
. Returns :ok
on success,
or {:error, reason}
on failure.
chown!(Path.t, non_neg_integer) :: :ok | no_return
Same as chown/2
, but raises an exception in case of failure. Otherwise :ok
.
Closes the file referenced by io_device
. It mostly returns :ok
, except
for some severe errors such as out of memory.
Note that if the option :delayed_write
was used when opening the file,
close/1
might return an old write error and not even try to close the file.
See open/2
for more information.
Copies the contents of source
to destination
.
Both parameters can be a filename or an IO device opened
with open/2
. bytes_count
specifies the number of
bytes to copy, the default being :infinity
.
If file destination
already exists, it is overwritten
by the contents in source
.
Returns {:ok, bytes_copied}
if successful,
{:error, reason}
otherwise.
Compared to the cp/3
, this function is more low-level,
allowing a copy from device to device limited by a number of
bytes. On the other hand, cp/3
performs more extensive
checks on both source and destination and it also preserves
the file mode after copy.
Typical error reasons are the same as in open/2
,
read/1
and write/3
.
The same as copy/3
but raises an File.CopyError
if it fails.
Returns the bytes_copied
otherwise.
Copies the contents in source
to destination
preserving its mode.
If a file already exists in the destination, it invokes a
callback which should return true
if the existing file
should be overwritten, false
otherwise. The callback defaults to return true
.
The function returns :ok
in case of success, returns
{:error, reason}
otherwise.
If you want to copy contents from an IO device to another device
or do a straight copy from a source to a destination without
preserving modes, check copy/3
instead.
Note: The command cp
in Unix systems behaves differently depending
if destination
is an existing directory or not. We have chosen to
explicitly disallow this behaviour. If destination is a directory, an
error will be returned.
The same as cp/3
, but raises File.CopyError
if it fails.
Returns :ok
otherwise.
Copies the contents in source to destination.
If the source is a file, it copies source
to
destination
. If the source is a directory, it copies
the contents inside source into the destination.
If a file already exists in the destination,
it invokes a callback which should return
true
if the existing file should be overwritten,
false
otherwise. The callback defaults to return true
.
If a directory already exists in the destination where a file is meant to be (or vice versa), this function will fail.
This function may fail while copying files, in such cases, it will leave the destination directory in a dirty state, where file which have already been copied won’t be removed.
The function returns {:ok, files_and_directories}
in case of
success, files_and_directories
lists all files and directories copied in no
specific order. It returns {:error, reason, file}
otherwise.
Note: The command cp
in Unix systems behaves differently
depending if destination
is an existing directory or not.
We have chosen to explicitly disallow this behaviour.
Examples
# Copies file "a.txt" to "b.txt"
File.cp_r "a.txt", "b.txt"
# Copies all files in "samples" to "tmp"
File.cp_r "samples", "tmp"
# Same as before, but asks the user how to proceed in case of conflicts
File.cp_r "samples", "tmp", fn(source, destination) ->
IO.gets("Overwriting #{destination} by #{source}. Type y to confirm. ") == "y\n"
end
The same as cp_r/3
, but raises File.CopyError
if it fails.
Returns the list of copied files otherwise.
Gets the current working directory.
In rare circumstances, this function can fail on Unix. It may happen
if read permissions do not exist for the parent directories of the
current directory. For this reason, returns {:ok, cwd}
in case
of success, {:error, reason}
otherwise.
The same as cwd/0
, but raises an exception if it fails.
Returns true
if the path is a directory.
Returns true
if the given path exists.
It can be regular file, directory, socket,
symbolic link, named pipe or device file.
Examples
File.exists?("test/")
#=> true
File.exists?("missing.txt")
#=> false
File.exists?("/dev/null")
#=> true
Creates a symbolic link new
to the file or directory existing
.
Returns :ok
if successful, {:error, reason}
otherwise.
If the operating system does not support symlinks, returns
{:error, :enotsup}
.
Returns the list of files in the given directory.
Returns {:ok, [files]}
in case of success,
{:error, reason}
otherwise.
The same as ls/1
but raises File.Error
in case of an error.
lstat(Path.t, stat_options) :: {:ok, File.Stat.t} | {:error, posix}
Returns information about the path
. If the file is a symlink, sets
the type
to :symlink
and returns a File.Stat
struct for the link. For any
other file, returns exactly the same values as stat/2
.
For more details, see :file.read_link_info/2
.
Options
The accepted options are:
:time
- configures how the file timestamps are returned
The values for :time
can be:
:universal
- returns a{date, time}
tuple in UTC (default):local
- returns a{date, time}
tuple using the machine time:posix
- returns the time as integer seconds since epoch
lstat!(Path.t, stat_options) :: File.Stat.t | no_return
Same as lstat/2
but returns the File.Stat
struct directly and
throws File.Error
if an error is returned.
Tries to create the directory path
. Missing parent directories are not created.
Returns :ok
if successful, or {:error, reason}
if an error occurs.
Typical error reasons are:
:eacces
- missing search or write permissions for the parent directories ofpath
:eexist
- there is already a file or directory namedpath
:enoent
- a component ofpath
does not exist:enospc
- there is no space left on the device:enotdir
- a component ofpath
is not a directory; on some platforms,:enoent
is returned instead
Same as mkdir/1
, but raises an exception in case of failure. Otherwise :ok
.
Tries to create the directory path
. Missing parent directories are created.
Returns :ok
if successful, or {:error, reason}
if an error occurs.
Typical error reasons are:
:eacces
- missing search or write permissions for the parent directories ofpath
:enospc
- there is no space left on the device:enotdir
- a component ofpath
is not a directory
Same as mkdir_p/1
, but raises an exception in case of failure. Otherwise :ok
.
Opens the given path
.
In order to write and read files, one must use the functions
in the IO
module. By default, a file is opened in :binary
mode,
which requires the functions IO.binread/2
and IO.binwrite/2
to interact with the file. A developer may pass :utf8
as an
option when opening the file and then all other functions from
IO
are available, since they work directly with Unicode data.
modes_or_function
can either be a list of modes or a function. If it’s a
list, it’s considered to be a list of modes (that are documented below). If
it’s a function, then it’s equivalent to calling open(path, [],
modes_or_function)
. See the documentation for open/3
for more information
on this function.
The allowed modes:
:binary
- opens the file in binary mode, disabling special handling of unicode sequences (default mode).: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 does exists, and if write is not combined with read, the file will be truncated.
:append
- the file will be opened for writing, and it will be created if it does not exist. Every write operation to a file opened with append will take place at the end of the file.:exclusive
- the file, when opened for writing, is created if it does not exist. If the file exists, open will return{:error, :eexist}
.:charlist
- when this term is given, read operations on the file will return charlists rather than binaries.:compressed
- makes it possible to read or write gzip compressed files.The compressed option must be combined with either read or write, but not both. Note that the file size obtained with
stat/1
will most probably not match the number of bytes that can be read from a compressed file.:utf8
- this option denotes how data is actually stored in the disk file and makes the file perform automatic translation of characters to and from UTF-8.If data is sent to a file in a format that cannot be converted to the UTF-8 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 will be closed.
:delayed_write
,:raw
,:ram
,:read_ahead
,:sync
,{:encoding, ...}
,{:read_ahead, pos_integer}
,{:delayed_write, non_neg_integer, non_neg_integer}
- for more information about these options see:file.open/2
.
This function returns:
{:ok, io_device}
- the file has been opened in the requested mode.io_device
is actually the PID of the process which handles the file. This process is linked to the process which originally opened the file. If any process to which theio_device
is linked terminates, the file will be closed and the process itself will be terminated.An
io_device
returned from this call can be used as an argument to theIO
module functions.{:error, reason}
- the file could not be opened.
Examples
{:ok, file} = File.open("foo.tar.gz", [:read, :compressed])
IO.read(file, :line)
File.close(file)
Similar to open/2
but expects a function as its last argument.
The file is opened, given to the function as an argument and automatically closed after the function returns, regardless if there was an error when executing the function.
Returns {:ok, function_result}
in case of success,
{:error, reason}
otherwise.
This function expects the file to be closed with success,
which is usually the case unless the :delayed_write
option
is given. For this reason, we do not recommend passing
:delayed_write
to this function.
Examples
File.open("file.txt", [:read, :write], fn(file) ->
IO.read(file, :line)
end)
See open/2
for the list of available modes
.
Similar to open/2
but raises an error if file could not be opened.
Returns the IO device otherwise.
See open/2
for the list of available modes.
Similar to open/3
but raises an error if file could not be opened.
If it succeeds opening the file, it returns the function
result on the IO device.
See open/2
for the list of available modes
.
Returns {:ok, binary}
, where binary
is a binary data object that contains the contents
of path
, 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 file name is not a directory; on some platforms,:enoent
is returned instead:enomem
- there is not enough memory for the contents of the file
You can use :file.format_error/1
to get a descriptive string of the error.
Returns a binary with the contents of the given filename or raises
File.Error
if an error occurs.
Renames the source
file to destination
file. It can be used to move files
(and directories) between directories. If moving a file, you must fully
specify the destination
filename, it is not sufficient to simply specify
its directory.
Returns :ok
in case of success, {:error, reason}
otherwise.
Note: The command mv
in Unix systems behaves differently depending
if source
is a file and the destination
is an existing directory.
We have chosen to explicitly disallow this behaviour.
Examples
# Rename file "a.txt" to "b.txt"
File.rename "a.txt", "b.txt"
# Rename directory "samples" to "tmp"
File.rename "samples", "tmp"
Tries to delete the file path
.
Returns :ok
if successful, or {:error, reason}
if an error occurs.
Note the file is deleted even if in read-only mode.
Typical error reasons are:
:enoent
- the file does not exist:eacces
- missing permission for the file or one of its parents:eperm
- the file is a directory and user is not super-user:enotdir
- a component of the file name is not a directory; on some platforms,:enoent
is returned instead:einval
- filename had an improper type, such as tuple
Examples
File.rm("file.txt")
#=> :ok
File.rm("tmp_dir/")
#=> {:error, :eperm}
Same as rm/1
, but raises an exception in case of failure. Otherwise :ok
.
Removes files and directories recursively at the given path
.
Symlinks are not followed but simply removed, non-existing
files are simply ignored (i.e. doesn’t make this function fail).
Returns {:ok, files_and_directories}
with all files and
directories removed in no specific order, {:error, reason, file}
otherwise.
Examples
File.rm_rf "samples"
#=> {:ok, ["samples", "samples/1.txt"]}
File.rm_rf "unknown"
#=> {:ok, []}
Same as rm_rf/1
but raises File.Error
in case of failures,
otherwise the list of files or directories removed.
Tries to delete the dir at path
.
Returns :ok
if successful, or {:error, reason}
if an error occurs.
Examples
File.rmdir('tmp_dir')
#=> :ok
File.rmdir('file.txt')
#=> {:error, :enotdir}
Same as rmdir/1
, but raises an exception in case of failure. Otherwise :ok
.
stat(Path.t, stat_options) :: {:ok, File.Stat.t} | {:error, posix}
Returns information about the path
. If it exists, it
returns a {:ok, info}
tuple, where info is a
File.Stat
struct. Returns {:error, reason}
with
the same reasons as read/1
if a failure occurs.
Options
The accepted options are:
:time
- configures how the file timestamps are returned
The values for :time
can be:
:universal
- returns a{date, time}
tuple in UTC (default):local
- returns a{date, time}
tuple using the same time zone as the machine:posix
- returns the time as integer seconds since epoch
stat!(Path.t, stat_options) :: File.Stat.t | no_return
Same as stat/2
but returns the File.Stat
directly and
throws File.Error
if an error is returned.
Returns a File.Stream
for the given path
with the given modes
.
The stream implements both Enumerable
and Collectable
protocols,
which means it can be used both for read and write.
The line_or_bytes
argument configures how the file is read when
streaming, by :line
(default) or by a given number of bytes.
Operating the stream can fail on open for the same reasons as
File.open!/2
. Note that the file is automatically opened each time streaming
begins. There is no need to pass :read
and :write
modes, as those are
automatically set by Elixir.
Raw files
Since Elixir controls when the streamed file is opened, the underlying
device cannot be shared and as such it is convenient to open the file
in raw mode for performance reasons. Therefore, Elixir will open
streams in :raw
mode with the :read_ahead
option unless an encoding
is specified. This means any data streamed into the file must be
converted to t:iodata/0
type. If you pass [:utf8]
in the modes parameter,
the underlying stream will use IO.write/2
and the String.Chars
protocol
to convert the data. See IO.binwrite/2
and IO.write/2
.
One may also consider passing the :delayed_write
option if the stream
is meant to be written to under a tight loop.
Examples
# Read in 2048 byte chunks rather than lines
File.stream!("./test/test.data", [], 2048)
#=> %File.Stream{line_or_bytes: 2048, modes: [:raw, :read_ahead, :binary],
#=> path: "./test/test.data", raw: true}
See Stream.run/1
for an example of streaming into a file.
Updates modification time (mtime) and access time (atime) of the given file.
The file is created if it doesn’t exist. Requires datetime in UTC.
touch!(Path.t, :calendar.datetime) :: :ok | no_return
Same as touch/2
but raises an exception if it fails.
Returns :ok
otherwise. Requires datetime in UTC.
Writes content
to the file path
.
The file is created if it does not exist. If it exists, the previous
contents are overwritten. Returns :ok
if successful, or {:error, reason}
if an error occurs.
content
must be iodata
(a list of bytes or a binary). Setting the
encoding for this function has no effect.
Warning: Every time this function is invoked, a file descriptor is opened
and a new process is spawned to write to the file. For this reason, if you are
doing multiple writes in a loop, opening the file via File.open/2
and using
the functions in IO
to write to the file will yield much better performance
than calling this function multiple times.
Typical error reasons are:
:enoent
- a component of the file name does not exist:enotdir
- a component of the file name is not a directory; on some platforms,:enoent
is returned instead:enospc
- there is no space 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
Check File.open/2
for other available options.
Same as write/3
but raises an exception if it fails, returns :ok
otherwise.
write_stat(Path.t, File.Stat.t, stat_options) :: :ok | {:error, posix}
Writes the given File.Stat
back to the filesystem at the given
path. Returns :ok
or {:error, reason}
.
write_stat!(Path.t, File.Stat.t, stat_options) :: :ok | no_return
Same as write_stat/3
but raises an exception if it fails.
Returns :ok
otherwise.