package eio

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Accessing paths on a file-system.

A _ Path.t represents a particular location in some filesystem. It is a pair of a base directory and a relative path from there.

Eio.Stdenv.cwd provides access to the current working directory. For example:

let ( / ) = Eio.Path.( / )

let run dir = ~create:(`Exclusive 0o600)
    (dir / "output.txt") "the data"

let () = @@ fun env ->
  run (Eio.Stdenv.cwd env)

It is normally not permitted to access anything above the base directory, even by following a symlink. The exception is Stdenv.fs, which provides access to the whole file-system:

Eio.Path.load (fs / "/etc/passwd")

In Eio, the directory separator is always "/", even on Windows. Use native to convert to a native path.

type 'a t = 'a Fs.dir * Fs.path

An OS directory FD and a path relative to it, for use with e.g. openat(2).

val (/) : 'a t -> string -> 'a t

t / step is t with step appended to t's path, or replacing t's path if step is absolute:

  • (fd, "foo") / "bar" = (fd, "foo/bar")
  • (fd, "foo") / "/bar" = (fd, "/bar")
val pp : _ t Fmt.t

pp formats a _ t as "<label:path>", suitable for logging.

val native : _ t -> string option

native t returns a path that can be used to refer to t with the host platform's native string-based file-system APIs, if available. This is intended for interoperability with non-Eio libraries.

This does not check for confinement (the resulting path might not be accessible via t itself). Also, if a directory was opened with open_dir and later renamed, this might use the old name.

Using strings as paths is not secure if components in the path can be replaced by symlinks while the path is being used. For example, if you try to write to "/home/mal/output.txt" just as mal replaces "output.txt" with a symlink to "/etc/passwd".

val native_exn : _ t -> string

Like native, but raise a suitable exception if the path is not a native path.

val split : 'a t -> ('a t * string) option

split t returns Some (dir, basename), where basename is the last path component in t and dir is t without basename.

dir / basename refers to the same path as t.

split t = None if there is nothing to split.

For example:

  • split (root, "foo/bar") = Some ((root, "foo"), "bar")
  • split (root, "/foo/bar") = Some ((root, "/foo"), "bar")
  • split (root, "/foo/bar/baz") = Some ((root, "/foo/bar"), "baz")
  • split (root, "/foo/bar//baz/") = Some ((root, "/foo/bar"), "baz")
  • split (root, "bar") = Some ((root, ""), "bar")
  • split (root, ".") = Some ((root, ""), ".")
  • split (root, "") = None
  • split (root, "/") = None

Reading files

val load : _ t -> string

load t returns the contents of the given file.

This is a convenience wrapper around with_open_in.

val open_in : sw:Switch.t -> _ t -> File.ro_ty Std.r

open_in ~sw t opens t for reading.

Note: files are always opened in binary mode.

val with_open_in : _ t -> (File.ro_ty Std.r -> 'a) -> 'a

with_open_in is like open_in, but calls fn flow with the new flow and closes it automatically when fn returns (if it hasn't already been closed by then).

val with_lines : _ t -> (string Stdlib.Seq.t -> 'a) -> 'a

with_lines t fn is a convenience function for streaming the lines of the file.

It uses Buf_read.lines.

Writing files

val save : ?append:bool -> create:Fs.create -> _ t -> string -> unit

save t data ~create writes data to t.

This is a convenience wrapper around with_open_out.

val open_out : sw:Switch.t -> ?append:bool -> create:Fs.create -> _ t -> File.rw_ty Resource.t

open_out ~sw t opens t for reading and writing.

Note: files are always opened in binary mode.

  • parameter append

    Open for appending: always write at end of file.

  • parameter create

    Controls whether to create the file, and what permissions to give it if so.

val with_open_out : ?append:bool -> create:Fs.create -> _ t -> (File.rw_ty Std.r -> 'a) -> 'a

with_open_out is like open_out, but calls fn flow with the new flow and closes it automatically when fn returns (if it hasn't already been closed by then).


val mkdir : perm:File.Unix_perm.t -> _ t -> unit

mkdir ~perm t creates a new directory t with permissions perm.

val mkdirs : ?exists_ok:bool -> perm:File.Unix_perm.t -> _ t -> unit

mkdirs ~perm t creates directory t along with any missing ancestor directories, recursively.

All created directories get permissions perm, but existing directories do not have their permissions changed.

val open_dir : sw:Switch.t -> _ t -> [< `Close | Fs.dir_ty ] t

open_dir ~sw t opens t.

This can be passed to functions to grant access only to the subtree t.

val with_open_dir : _ t -> ([< `Close | Fs.dir_ty ] t -> 'a) -> 'a

with_open_dir is like open_dir, but calls fn dir with the new directory and closes it automatically when fn returns (if it hasn't already been closed by then).

val read_dir : _ t -> string list

read_dir t reads directory entries for t.

The entries are sorted using

Note: The special Unix entries "." and ".." are not included in the results.


val stat : follow:bool -> _ t -> File.Stat.t

stat ~follow t returns metadata about the file t.

If t is a symlink, the information returned is about the target if follow = true, otherwise it is about the link itself.

val kind : follow:bool -> _ t -> [ File.Stat.kind | `Not_found ]

kind ~follow t is the type of t, or `Not_found if it doesn't exist.

  • parameter follow

    If true and t is a symlink, return the type of the target rather than `Symbolic_link.

val is_file : _ t -> bool

is_file t is true if t is a regular file, and false if it doesn't exist or has a different type.

is_file t is kind ~follow:true t = `Regular_file.

val is_directory : _ t -> bool

is_directory t is true if t is a directory, and false if it doesn't exist or has a different type.

is_directory t is kind ~follow:true t = `Directory.

read_link t is the target of symlink t.


unlink t removes directory entry t.

Note: this cannot be used to unlink directories. Use rmdir for directories.

val rmdir : _ t -> unit

rmdir t removes directory entry t. This only works when the entry is itself a directory.

Note: this usually requires the directory to be empty.

val rmtree : ?missing_ok:bool -> _ t -> unit

rmtree t removes t (and its contents, recursively, if it's a directory).

  • parameter missing_ok

    If false (the default), raise an Fs.error.Not_found IO error if t doesn't exist. If true, ignore missing items. This applies recursively, allowing two processes to attempt to remove a tree at the same time.

val rename : _ t -> _ t -> unit

rename old_t new_t atomically unlinks old_t and links it as new_t.

If new_t already exists, it is atomically replaced.


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