---
name: "Filename"
section: "3o"
platform: "linux"
package: "ocaml"
version: "5.5.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Filename"
---

# Filename(3o)

Operations on file names.

## NAME

Filename - Operations on file names.

## Module

Module   Filename

## Documentation

Module **Filename**\
  :  **sig end**

Operations on file names.

*val current\_dir\_name* :  **string**

The conventional name for the current directory (e.g.  **.** in Unix).

*val parent\_dir\_name* :  **string**

The conventional name for the parent of the current directory (e.g.  **..** in Unix).

*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** .

*val is\_relative* :  **string -\> bool**

Return  **true** if the file name is relative to the current directory,  **false** if it is absolute (i.e. in Unix, starts with  **/** ).

*val is\_implicit* :  **string -\> bool**

Return  **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.

*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**

Return 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.

**Before3.11.2** 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** ).

**Before4.03** no ?perms optional argument

**Before3.11.2** 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** and  **?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.