Filename(3)

okay bestie, this is the Filename(3) page from the OCaml library manual, and it's literally all about operations on file names ✨💅

🌸 NAME 🌸

Operations on file names. That's the whole assignment, no cap.

🧩 Module 🧩

The module is Filename — like, literally Module Filename. Main character module energy 👑

💖 Documentation 💖

Module Filename : sig end

Operations on file names. Yes, again — the docs said it twice and we are not skipping the “boring” parts, bestie 🫶

Here are all the vals, in order, with the signatures kept verbatim because that's the whole point:

• val current_dir_name : string — the conventional name for the current directory (e.g. . in Unix). It's giving “where am I” but make it a string 🫶
• val parent_dir_name : string — the conventional name for the parent of the current directory (e.g. .. in Unix). Iconic “go up one” behavior.
• val dir_sep : string — the directory separator (e.g. / in Unix).
  • Since 3.11.2.
• val concat : string -> string -> string — concat dir file returns a file name that designates file file in directory dir. Yes, it's the “put these two together” slay ✨
• val is_relative : string -> bool — returns true if the file name is relative to the current directory, and false if it is absolute (i.e. in Unix, starts with /). Vibe check: relative or absolute?
• val is_implicit : string -> bool — returns true if the file name is relative and does not start with an explicit reference to the current directory (./ or ../ in Unix); false if it starts with an explicit reference to the root directory or the current directory. Lowkey “is this path being sneaky about where it starts?”
• val check_suffix : string -> string -> bool — check_suffix name suff returns true if the filename name ends with the suffix suff.
  • Under Windows ports (including Cygwin), comparison is case-insensitive, relying on String.lowercase_ascii. Note that this does not match exactly the interpretation of case-insensitive filename equivalence from Windows.
• val chop_suffix : string -> string -> string — chop_suffix name suff removes the suffix suff from the filename name.
  • Raises Invalid_argument if name does not end with the suffix suff.
• val chop_suffix_opt : suffix:string -> string -> string option — chop_suffix_opt ~suffix filename removes the suffix from the filename if possible, or returns None if the filename does not end with the suffix.
  • Under Windows ports (including Cygwin), comparison is case-insensitive, relying on String.lowercase_ascii. Note that this does not match exactly the interpretation of case-insensitive filename equivalence from Windows.
  • Since 4.08.
• val extension : string -> string — extension name is the shortest suffix ext of name0 where:
  • name0 is the longest suffix of name that does not contain a directory separator;
  • ext starts with a period;
  • ext is preceded by at least one non-period character in name0. If such a suffix does not exist, extension name is the empty string.
  • Since 4.04.
• val remove_extension : string -> string — returns the given file name without its extension, as defined in Filename.extension. If the extension is empty, the function returns the given file name.
  • The following invariant holds for any file name s: remove_extension s ^ extension s = s
  • Since 4.04.
• val chop_extension : string -> string — same as Filename.remove_extension, but raise Invalid_argument if the given name has an empty extension.
• val basename : string -> string — split a file name into directory name / base file name. If name is a valid file name, then concat (dirname name) (basename name) returns a file name which is equivalent to name. Moreover, after setting the current directory to dirname name (with Sys.chdir), references to basename name (which is a relative file name) designate the same file as name before the call to Sys.chdir.
  • This function conforms to the specification of POSIX.1-2008 for the basename utility.
• val dirname : string -> string — see Filename.basename. This function conforms to the specification of POSIX.1-2008 for the dirname utility.
• val null : string — null is "/dev/null" on POSIX and "NUL" on Windows. It represents a file on the OS that discards all writes and returns end of file on reads.
  • Since 4.10.
• val temp_file : ?temp_dir:string -> string -> string -> string — temp_file prefix suffix returns the name of a fresh temporary file in the temporary directory. The base name of the temporary file is formed by concatenating prefix, then a suitably chosen integer number, then suffix. The optional argument temp_dir indicates the temporary directory to use, defaulting to the current result of Filename.get_temp_dir_name. The temporary file is created empty, with permissions 0o600 (readable and writable only by the file owner). The file is guaranteed to be different from any other file that existed when temp_file was called.
  • Before 3.11.2, there was no ?temp_dir optional argument.
  • Raises Sys_error if the file could not be created.
• val open_temp_file : ?mode:open_flag list -> ?perms:int -> ?temp_dir:string -> string -> string -> string * out_channel — same as Filename.temp_file, but returns both the name of a fresh temporary file and an output channel opened (atomically) on this file. This function is more secure than temp_file: there is no risk that the temporary file will be modified (e.g. replaced by a symbolic link) before the program opens it. The optional argument mode is a list of additional flags to control the opening of the file. It can contain one or several of Open_append, Open_binary, and Open_text. The default is [Open_text] (open in text mode). The file is created with permissions perms (defaults to readable and writable only by the file owner, 0o600).
  • Before 4.03, there was no ?perms optional argument.
  • Before 3.11.2, there was no ?temp_dir optional argument.
  • Raises Sys_error if the file could not be opened.
• val temp_dir : ?temp_dir:string -> ?perms:int -> string -> string -> string — temp_dir prefix suffix creates and returns the name of a fresh temporary directory with permissions perms (defaults to 0o700) inside temp_dir. The base name of the temporary directory is formed by concatenating prefix, then a suitably chosen integer number, then suffix. The optional argument temp_dir indicates the temporary directory to use, defaulting to the current result of Filename.get_temp_dir_name. The temporary directory is created empty, with permissions 0o700 (readable, writable, and searchable only by the file owner). The directory is guaranteed to be different from any other directory that existed when temp_dir was called.
  • If temp_dir does not exist, this function does not create it. Instead, it raises Sys_error.
  • Since 5.1.
  • Raises Sys_error if the directory could not be created.
• val get_temp_dir_name : unit -> string — the name of the temporary directory. Under Unix, the value of the TMPDIR environment variable, or "/tmp" if the variable is not set.
  • Under Windows, the value returned by GetTempPath2 (if available) or GetTempPath.
  • The temporary directory can be changed with Filename.set_temp_dir_name.
  • Under Windows, before OCaml 5.4, it would return the value of the TEMP environment variable, or "." if the variable was not set.
  • Since 4.00.
• val set_temp_dir_name : string -> unit — change the temporary directory returned by Filename.get_temp_dir_name and used by Filename.temp_file and Filename.open_temp_file. The temporary directory is a domain-local value which is inherited by child domains.
  • Since 4.00.
• val quote : string -> string — return a quoted version of a file name, suitable for use as one argument in a command line, escaping all meta-characters.
  • Warning: under Windows, the output is only suitable for use with programs that follow the standard Windows quoting conventions.
• val quote_command : string -> ?stdin:string -> ?stdout:string -> ?stderr:string -> string list -> string — quote_command cmd args returns a quoted command line, suitable for use as an argument to Sys.command, Unix.system, and the Unix.open_process functions.
  • The string cmd is the command to call. The list args is the list of arguments to pass to this command. It can be empty.
  • The optional arguments ?stdin, ?stdout, and ?stderr are file names used to redirect the standard input, the standard output, or the standard error of the command.
  • If ~stdin:f is given, a redirection < f is performed and the standard input of the command reads from file f.
  • If ~stdout:f is given, a redirection > f is performed and the standard output of the command is written to file f.
  • If ~stderr:f is given, a redirection 2> f is performed and the standard error of the command is written to file f.
  • If both ~stdout:f and ~stderr:f are given, with the exact same file name f, a 2>&1 redirection is performed so that the standard output and the standard error of the command are interleaved and redirected to the same file f.
  • Under Unix and Cygwin, the command, the arguments, and the redirections if any are quoted using Filename.quote, then concatenated. Under Win32, additional quoting is performed as required by the cmd.exe shell that is called by Sys.command.
  • Since 4.10.
  • Raises Failure if the command cannot be escaped on the current platform.

💖 sign-off time: source/version is OCamldoc, date is 2026-06-22, and the manual is Filename(3). Bye bestie, go name some files! 🫶✨