# Elixir v1.10.3 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`.

Paths given to functions in this module can be either relative to the current working directory (as returned by `File.cwd/0`), or absolute paths. Shell conventions like `~` are not expanded automatically. To use paths like `~/Downloads`, you can use `Path.expand/1` or `Path.expand/2` to expand your path to an absolute path.

## 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 operating system 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

## Types

encoding_mode()
erlang_time()
io_device()
mode()
posix()
posix_time()
stat_options()
stream_mode()

## Functions

cd(path)

Sets the current working directory.

cd!(path)

The same as `cd/1`, but raises a `File.Error` exception if it fails.

cd!(path, function)

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.

chgrp(path, gid)

Changes the group given by the group ID `gid` for a given `file`. Returns `:ok` on success, or `{:error, reason}` on failure.

chgrp!(path, gid)

Same as `chgrp/2`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

chmod(path, mode)

Changes the `mode` for a given `file`.

chmod!(path, mode)

Same as `chmod/2`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

chown(path, uid)

Changes the owner given by the user ID `uid` for a given `file`. Returns `:ok` on success, or `{:error, reason}` on failure.

chown!(path, uid)

Same as `chown/2`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

close(io_device)

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

copy(source, destination, bytes_count \\ :infinity)

Copies the contents of `source` to `destination`.

copy!(source, destination, bytes_count \\ :infinity)

The same as `copy/3` but raises a `File.CopyError` exception if it fails. Returns the `bytes_copied` otherwise.

cp(source_file, destination_file, callback \\ fn _, _ -> true end)

Copies the contents in `source_file` to `destination_file` preserving its modes.

cp!(source_file, destination_file, callback \\ fn _, _ -> true end)

The same as `cp/3`, but raises a `File.CopyError` exception if it fails. Returns `:ok` otherwise.

cp_r(source, destination, callback \\ fn _, _ -> true end)

Copies the contents in `source` to `destination` recursively, maintaining the source directory structure and modes.

cp_r!(source, destination, callback \\ fn _, _ -> true end)

The same as `cp_r/3`, but raises a `File.CopyError` exception if it fails. Returns the list of copied files otherwise.

cwd()

Gets the current working directory.

cwd!()

The same as `cwd/0`, but raises a `File.Error` exception if it fails.

dir?(path, opts \\ [])

Returns `true` if the given path is a directory.

exists?(path, opts \\ [])

Returns `true` if the given path exists.

ln(existing, new)

Creates a hard link `new` to the file `existing`.

ln!(existing, new)

Same as `ln/2` but raises a `File.LinkError` exception if it fails. Returns `:ok` otherwise.

ln_s(existing, new)

Creates a symbolic link `new` to the file or directory `existing`.

ln_s!(existing, new)

Same as `ln_s/2` but raises a `File.LinkError` exception if it fails. Returns `:ok` otherwise.

ls(path \\ ".")

Returns the list of files in the given directory.

ls!(path \\ ".")

The same as `ls/1` but raises a `File.Error` exception in case of an error.

lstat(path, opts \\ [])

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`.

lstat!(path, opts \\ [])

Same as `lstat/2` but returns the `File.Stat` struct directly, or raises a `File.Error` exception if an error is returned.

mkdir(path)

Tries to create the directory `path`.

mkdir!(path)

Same as `mkdir/1`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

mkdir_p(path)

Tries to create the directory `path`.

mkdir_p!(path)

Same as `mkdir_p/1`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

open(path, modes_or_function \\ [])

Opens the given `path`.

open(path, modes, function)

Similar to `open/2` but expects a function as its last argument.

open!(path, modes_or_function \\ [])

Similar to `open/2` but raises a `File.Error` exception if the file could not be opened. Returns the IO device otherwise.

open!(path, modes, function)

Similar to `open/3` but raises a `File.Error` exception if the file could not be opened.

read(path)

Returns `{:ok, binary}`, where `binary` is a binary data object that contains the contents of `path`, or `{:error, reason}` if an error occurs.

read!(path)

Returns a binary with the contents of the given filename, or raises a `File.Error` exception if an error occurs.

read_link(path)

Reads the symbolic link at `path`.

read_link!(path)

Same as `read_link/1` but returns the target directly, or raises a `File.Error` exception if an error is returned.

regular?(path, opts \\ [])

Returns `true` if the path is a regular file.

rename(source, destination)

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.

rename!(source, destination)

The same as `rename/2` but raises a `File.RenameError` exception if it fails. Returns `:ok` otherwise.

rm(path)

Tries to delete the file `path`.

rm!(path)

Same as `rm/1`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

rm_rf(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).

rm_rf!(path)

Same as `rm_rf/1` but raises a `File.Error` exception in case of failures, otherwise the list of files or directories removed.

rmdir(path)

Tries to delete the dir at `path`.

rmdir!(path)

Same as `rmdir/1`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

stat(path, opts \\ [])

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.

stat!(path, opts \\ [])

Same as `stat/2` but returns the `File.Stat` directly, or raises a `File.Error` exception if an error is returned.

stream!(path, modes \\ [], line_or_bytes \\ :line)

Returns a `File.Stream` for the given `path` with the given `modes`.

touch(path, time \\ System.os_time(:second))

Updates modification time (mtime) and access time (atime) of the given file.

touch!(path, time \\ System.os_time(:second))

Same as `touch/2` but raises a `File.Error` exception if it fails. Returns `:ok` otherwise.

write(path, content, modes \\ [])

Writes `content` to the file `path`.

write!(path, content, modes \\ [])

Same as `write/3` but raises a `File.Error` exception if it fails. Returns `:ok` otherwise.

write_stat(path, stat, opts \\ [])

Writes the given `File.Stat` back to the file system at the given path. Returns `:ok` or `{:error, reason}`.

write_stat!(path, stat, opts \\ [])

Same as `write_stat/3` but raises a `File.Error` exception if it fails. Returns `:ok` otherwise.

# Link to this section Types

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# encoding_mode()

View Source

## Specs

    encoding_mode() ::
      :utf8
      | {:encoding,
         :latin1
         | :unicode
         | :utf8
         | :utf16
         | :utf32
         | {:utf16, :big | :little}
         | {:utf32, :big | :little}}

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# erlang_time()

View Source

## Specs

    erlang_time() ::
      {{year :: non_neg_integer(), month :: 1..12, day :: 1..31},
       {hour :: 0..23, minute :: 0..59, second :: 0..59}}

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# io_device()

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## Specs

    io_device() :: :file.io_device()

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# mode()

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## Specs

    mode() ::
      :append
      | :binary
      | :charlist
      | :compressed
      | :delayed_write
      | :exclusive
      | :raw
      | :read
      | :read_ahead
      | :sync
      | :write
      | {:read_ahead, pos_integer()}
      | {:delayed_write, non_neg_integer(), non_neg_integer()}
      | encoding_mode()

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# posix()

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## Specs

    posix() :: :file.posix()

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# posix_time()

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## Specs

    posix_time() :: integer()

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# stat_options()

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## Specs

    stat_options() :: [{:time, :local | :universal | :posix}]

Link to this type

# stream_mode()

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## Specs

    stream_mode() ::
      encoding_mode()
      | :trim_bom
      | {:read_ahead, pos_integer() | false}
      | {:delayed_write, non_neg_integer(), non_neg_integer()}

# Link to this section Functions

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# cd(path)

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## Specs

    cd(Path.t()) :: :ok | {:error, posix()}

Sets the current working directory.

Returns `:ok` if successful, `{:error, reason}` otherwise.

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# cd!(path)

View Source

## Specs

    cd!(Path.t()) :: :ok

The same as `cd/1`, but raises a `File.Error` exception if it fails.

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# cd!(path, function)

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## Specs

    cd!(Path.t(), (() -> res)) :: res 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.

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# chgrp(path, gid)

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## Specs

    chgrp(Path.t(), non_neg_integer()) :: :ok | {:error, posix()}

Changes the group given by the group ID `gid` for a given `file`. Returns `:ok` on success, or `{:error, reason}` on failure.

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# chgrp!(path, gid)

View Source

## Specs

    chgrp!(Path.t(), non_neg_integer()) :: :ok

Same as `chgrp/2`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

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# chmod(path, mode)

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## Specs

    chmod(Path.t(), non_neg_integer()) :: :ok | {:error, posix()}

Changes the `mode` for a given `file`.

Returns `:ok` on success, or `{:error, reason}` on failure.

## Permissions

File permissions are specified by adding together the following octal modes:

- `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.

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# chmod!(path, mode)

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## Specs

    chmod!(Path.t(), non_neg_integer()) :: :ok

Same as `chmod/2`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

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# chown(path, uid)

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## Specs

    chown(Path.t(), non_neg_integer()) :: :ok | {:error, posix()}

Changes the owner given by the user ID `uid` for a given `file`. Returns `:ok` on success, or `{:error, reason}` on failure.

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# chown!(path, uid)

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## Specs

    chown!(Path.t(), non_neg_integer()) :: :ok

Same as `chown/2`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

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# close(io_device)

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## Specs

    close(io_device()) :: :ok | {:error, posix() | :badarg | :terminated}

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.

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# copy(source, destination, bytes_count \\ :infinity)

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## Specs

    copy(Path.t() | io_device(), Path.t() | io_device(), pos_integer() | :infinity) ::
      {:ok, non_neg_integer()} | {:error, posix()}

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`.

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# copy!(source, destination, bytes_count \\ :infinity)

View Source

## Specs

    copy!(Path.t() | io_device(), Path.t() | io_device(), pos_integer() | :infinity) ::
      non_neg_integer()

The same as `copy/3` but raises a `File.CopyError` exception if it fails. Returns the `bytes_copied` otherwise.

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# cp(source_file, destination_file, callback \\ fn _, _ -> true end)

View Source

## Specs

    cp(Path.t(), Path.t(), (Path.t(), Path.t() -> boolean())) ::
      :ok | {:error, posix()}

Copies the contents in `source_file` to `destination_file` preserving its modes.

`source_file` and `destination_file` must be a file or a symbolic link to one, or in the case of destination, a path to a non-existent file. If either one of them is a directory, `{:error, :eisdir}` will be returned.

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. Otherwise, it returns `{:error, reason}`.

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-like systems behaves differently depending on whether the destination is an existing directory or not. We have chosen to explicitly disallow copying to a destination which is a directory, and an error will be returned if tried.

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# cp!(source_file, destination_file, callback \\ fn _, _ -> true end)

View Source

## Specs

    cp!(Path.t(), Path.t(), (Path.t(), Path.t() -> boolean())) :: :ok

The same as `cp/3`, but raises a `File.CopyError` exception if it fails. Returns `:ok` otherwise.

Link to this function

# cp_r(source, destination, callback \\ fn _, _ -> true end)

View Source

## Specs

    cp_r(Path.t(), Path.t(), (Path.t(), Path.t() -> boolean())) ::
      {:ok, [binary()]} | {:error, posix(), binary()}

Copies the contents in `source` to `destination` recursively, maintaining the source directory structure and modes.

If `source` is a file or a symbolic link to it, `destination` must be a path to an existent file, a symbolic link to one, or a path to a non-existent file.

If `source` is a directory, or a symbolic link to it, then `destination` must be an existent `directory` or a symbolic link to one, or a path to a non-existent directory.

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` directory.

If a file already exists in the destination, it invokes `callback`. `callback` must be a function that takes two arguments: `source` and `destination`. The callback should return `true` if the existing file should be overwritten and `false` otherwise.

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-like systems behaves differently depending on whether `destination` is an existing directory or not. We have chosen to explicitly disallow this behaviour. If `source` is a `file` and `destination` is a directory, `{:error, :eisdir}` will be returned.

## 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)

Link to this function

# cp_r!(source, destination, callback \\ fn _, _ -> true end)

View Source

## Specs

    cp_r!(Path.t(), Path.t(), (Path.t(), Path.t() -> boolean())) :: [binary()]

The same as `cp_r/3`, but raises a `File.CopyError` exception if it fails. Returns the list of copied files otherwise.

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# cwd()

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## Specs

    cwd() :: {:ok, binary()} | {:error, posix()}

Gets the current working directory.

In rare circumstances, this function can fail on Unix-like systems. 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.

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# cwd!()

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## Specs

    cwd!() :: binary()

The same as `cwd/0`, but raises a `File.Error` exception if it fails.

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# dir?(path, opts \\ [])

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## Specs

    dir?(Path.t(), [dir_option]) :: boolean() when dir_option: :raw

Returns `true` if the given path is a directory.

This function follows symbolic links, so if a symbolic link points to a directory, `true` is returned.

## Options

The supported options are:

- `:raw` - a single atom to bypass the file server and only check for the file locally

## Examples

    File.dir?("./test")
    #=> true

    File.dir?("test")
    #=> true

    File.dir?("/usr/bin")
    #=> true

    File.dir?("~/Downloads")
    #=> false

    "~/Downloads" |> Path.expand() |> File.dir?()
    #=> true

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# exists?(path, opts \\ [])

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## Specs

    exists?(Path.t(), [exists_option]) :: boolean() when exists_option: :raw

Returns `true` if the given path exists.

It can be a regular file, directory, socket, symbolic link, named pipe, or device file. Returns `false` for symbolic links pointing to non-existing targets.

## Options

The supported options are:

- `:raw` - a single atom to bypass the file server and only check for the file locally

## Examples

    File.exists?("test/")
    #=> true

    File.exists?("missing.txt")
    #=> false

    File.exists?("/dev/null")
    #=> true

Link to this function

# ln(existing, new)

View Source (since 1.5.0)

## Specs

    ln(Path.t(), Path.t()) :: :ok | {:error, posix()}

Creates a hard link `new` to the file `existing`.

Returns `:ok` if successful, `{:error, reason}` otherwise. If the operating system does not support hard links, returns `{:error, :enotsup}`.

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# ln!(existing, new)

View Source (since 1.5.0)

## Specs

    ln!(Path.t(), Path.t()) :: :ok

Same as `ln/2` but raises a `File.LinkError` exception if it fails. Returns `:ok` otherwise.

Link to this function

# ln_s(existing, new)

View Source (since 1.5.0)

## Specs

    ln_s(Path.t(), Path.t()) :: :ok | {:error, posix()}

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}`.

Link to this function

# ln_s!(existing, new)

View Source

## Specs

    ln_s!(Path.t(), Path.t()) :: :ok

Same as `ln_s/2` but raises a `File.LinkError` exception if it fails. Returns `:ok` otherwise.

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# ls(path \\ ".")

View Source

## Specs

    ls(Path.t()) :: {:ok, [binary()]} | {:error, posix()}

Returns the list of files in the given directory.

Returns `{:ok, files}` in case of success, `{:error, reason}` otherwise.

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# ls!(path \\ ".")

View Source

## Specs

    ls!(Path.t()) :: [binary()]

The same as `ls/1` but raises a `File.Error` exception in case of an error.

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# lstat(path, opts \\ [])

View Source

## Specs

    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

Note: Since file times are stored in POSIX time format on most operating systems, it is faster to retrieve file information with the `time: :posix` option.

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# lstat!(path, opts \\ [])

View Source

## Specs

    lstat!(Path.t(), stat_options()) :: File.Stat.t()

Same as `lstat/2` but returns the `File.Stat` struct directly, or raises a `File.Error` exception if an error is returned.

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# mkdir(path)

View Source

## Specs

    mkdir(Path.t()) :: :ok | {:error, posix()}

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 of `path`
- `:eexist` - there is already a file or directory named `path`
- `:enoent` - a component of `path` does not exist
- `:enospc` - there is no space left on the device
- `:enotdir` - a component of `path` is not a directory; on some platforms, `:enoent` is returned instead

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# mkdir!(path)

View Source

## Specs

    mkdir!(Path.t()) :: :ok

Same as `mkdir/1`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

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# mkdir_p(path)

View Source

## Specs

    mkdir_p(Path.t()) :: :ok | {:error, posix()}

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 of `path`
- `:enospc` - there is no space left on the device
- `:enotdir` - a component of `path` is not a directory

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# mkdir_p!(path)

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## Specs

    mkdir_p!(Path.t()) :: :ok

Same as `mkdir_p/1`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

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# open(path, modes_or_function \\ [])

View Source

## Specs

    open(Path.t(), [mode() | :ram]) :: {:ok, io_device()} | {:error, posix()}

    open(Path.t(), (io_device() -> res)) :: {:ok, res} | {:error, posix()}
    when res: var

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 monitors the process that originally opened the file (the owner process). If the owner process terminates, the file is closed and the process itself terminates too. If any process to which the `io_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 the `IO` 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)

Link to this function

# open(path, modes, function)

View Source

## Specs

    open(Path.t(), [mode() | :ram], (io_device() -> res)) ::
      {:ok, res} | {:error, posix()}
    when res: var

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`.

Link to this function

# open!(path, modes_or_function \\ [])

View Source

## Specs

    open!(Path.t(), [mode() | :ram]) :: io_device()

    open!(Path.t(), (io_device() -> res)) :: res when res: var

Similar to `open/2` but raises a `File.Error` exception if the file could not be opened. Returns the IO device otherwise.

See `open/2` for the list of available modes.

Link to this function

# open!(path, modes, function)

View Source

## Specs

    open!(Path.t(), [mode() | :ram], (io_device() -> res)) :: res when res: var

Similar to `open/3` but raises a `File.Error` exception if the 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`.

Link to this function

# read(path)

View Source

## Specs

    read(Path.t()) :: {:ok, binary()} | {:error, posix()}

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.

Link to this function

# read!(path)

View Source

## Specs

    read!(Path.t()) :: binary()

Returns a binary with the contents of the given filename, or raises a `File.Error` exception if an error occurs.

Link to this function

# read_link(path)

View Source (since 1.5.0)

## Specs

    read_link(Path.t()) :: {:ok, binary()} | {:error, posix()}

Reads the symbolic link at `path`.

If `path` exists and is a symlink, returns `{:ok, target}`, otherwise returns `{:error, reason}`.

For more details, see `:file.read_link/1`.

Typical error reasons are:

- `:einval` - path is not a symbolic link
- `:enoent` - path does not exist
- `:enotsup` - symbolic links are not supported on the current platform

Link to this function

# read_link!(path)

View Source (since 1.5.0)

## Specs

    read_link!(Path.t()) :: binary()

Same as `read_link/1` but returns the target directly, or raises a `File.Error` exception if an error is returned.

Link to this function

# regular?(path, opts \\ [])

View Source

## Specs

    regular?(Path.t(), [regular_option]) :: boolean() when regular_option: :raw

Returns `true` if the path is a regular file.

This function follows symbolic links, so if a symbolic link points to a regular file, `true` is returned.

## Options

The supported options are:

- `:raw` - a single atom to bypass the file server and only check for the file locally

## Examples

    File.regular?(__ENV__.file)
    #=> true

Link to this function

# rename(source, destination)

View Source

## Specs

    rename(Path.t(), Path.t()) :: :ok | {:error, posix()}

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-like systems behaves differently depending on whether `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")

Link to this function

# rename!(source, destination)

View Source (since 1.9.0)

## Specs

    rename!(Path.t(), Path.t()) :: :ok

The same as `rename/2` but raises a `File.RenameError` exception if it fails. Returns `:ok` otherwise.

Link to this function

# rm(path)

View Source

## Specs

    rm(Path.t()) :: :ok | {:error, posix()}

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}

Link to this function

# rm!(path)

View Source

## Specs

    rm!(Path.t()) :: :ok

Same as `rm/1`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

Link to this function

# rm_rf(path)

View Source

## Specs

    rm_rf(Path.t()) :: {:ok, [binary()]} | {:error, posix(), binary()}

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, []}

Link to this function

# rm_rf!(path)

View Source

## Specs

    rm_rf!(Path.t()) :: [binary()]

Same as `rm_rf/1` but raises a `File.Error` exception in case of failures, otherwise the list of files or directories removed.

Link to this function

# rmdir(path)

View Source

## Specs

    rmdir(Path.t()) :: :ok | {:error, posix()}

Tries to delete the dir at `path`.

Returns `:ok` if successful, or `{:error, reason}` if an error occurs. It returns `{:error, :eexist}` if the directory is not empty.

## Examples

    File.rmdir("tmp_dir")
    #=> :ok

    File.rmdir("non_empty_dir")
    #=> {:error, :eexist}

    File.rmdir("file.txt")
    #=> {:error, :enotdir}

Link to this function

# rmdir!(path)

View Source

## Specs

    rmdir!(Path.t()) :: :ok | {:error, posix()}

Same as `rmdir/1`, but raises a `File.Error` exception in case of failure. Otherwise `:ok`.

Link to this function

# stat(path, opts \\ [])

View Source

## Specs

    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

Note: Since file times are stored in POSIX time format on most operating systems, it is faster to retrieve file information with the `time: :posix` option.

Link to this function

# stat!(path, opts \\ [])

View Source

## Specs

    stat!(Path.t(), stat_options()) :: File.Stat.t()

Same as `stat/2` but returns the `File.Stat` directly, or raises a `File.Error` exception if an error is returned.

Link to this function

# stream!(path, modes \\ [], line_or_bytes \\ :line)

View Source

## Specs

    stream!(Path.t(), stream_mode(), :line | pos_integer()) :: File.Stream.t()

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, for example, `[encoding: :utf8]` or `[encoding: {:utf16, :little}]` 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.

## Byte order marks

If you pass `:trim_bom` in the modes parameter, the stream will trim UTF-8, UTF-16 and UTF-32 byte order marks when reading from file.

Note that this function does not try to discover the file encoding basing on BOM.

## 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.

Link to this function

# touch(path, time \\ System.os_time(:second))

View Source

## Specs

    touch(Path.t(), erlang_time() | posix_time()) :: :ok | {:error, posix()}

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 (as returned by `:erlang.universaltime()`) or an integer representing the POSIX timestamp (as returned by `System.os_time(:second)`).

In Unix-like systems, changing the modification time may require you to be either `root` or the owner of the file. Having write access may not be enough. In those cases, touching the file the first time (to create it) will succeed, but touching an existing file with fail with `{:error, :eperm}`.

## Examples

    File.touch("/tmp/a.txt", {{2018, 1, 30}, {13, 59, 59}})
    #=> :ok
    File.touch("/fakedir/b.txt", {{2018, 1, 30}, {13, 59, 59}})
    {:error, :enoent}

    File.touch("/tmp/a.txt", 1544519753)
    #=> :ok

Link to this function

# touch!(path, time \\ System.os_time(:second))

View Source

## Specs

    touch!(Path.t(), erlang_time() | posix_time()) :: :ok

Same as `touch/2` but raises a `File.Error` exception if it fails. Returns `:ok` otherwise.

The file is created if it doesn't exist. Requires datetime in UTC (as returned by `:erlang.universaltime()`) or an integer representing the POSIX timestamp (as returned by `System.os_time(:second)`).

## Examples

    File.touch!("/tmp/a.txt", {{2018, 1, 30}, {13, 59, 59}})
    #=> :ok
    File.touch!("/fakedir/b.txt", {{2018, 1, 30}, {13, 59, 59}})
    ** (File.Error) could not touch "/fakedir/b.txt": no such file or directory

    File.touch!("/tmp/a.txt", 1544519753)

Link to this function

# write(path, content, modes \\ [])

View Source

## Specs

    write(Path.t(), iodata(), [mode()]) :: :ok | {:error, posix()}

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.

Link to this function

# write!(path, content, modes \\ [])

View Source

## Specs

    write!(Path.t(), iodata(), [mode()]) :: :ok

Same as `write/3` but raises a `File.Error` exception if it fails. Returns `:ok` otherwise.

Link to this function

# write_stat(path, stat, opts \\ [])

View Source

## Specs

    write_stat(Path.t(), File.Stat.t(), stat_options()) :: :ok | {:error, posix()}

Writes the given `File.Stat` back to the file system at the given path. Returns `:ok` or `{:error, reason}`.

Link to this function

# write_stat!(path, stat, opts \\ [])

View Source

## Specs

    write_stat!(Path.t(), File.Stat.t(), stat_options()) :: :ok

Same as `write_stat/3` but raises a `File.Error` exception if it fails. Returns `:ok` otherwise.