Reference Manual


Table of Contents




Module Summary

File utilities, such as wildcard matching of filenames.


This module contains utilities on a higher level than the file module.

This module does not support "raw" filenames (that is, files whose names do not comply with the expected encoding). Such files are ignored by the functions in this module.

For more information about raw filenames, see the file module.


Functionality in this module generally assumes valid input and does not necessarily fail on input that does not use a valid encoding, but may instead very likely produce invalid output.

File operations used to accept filenames containing null characters (integer value zero). This caused the name to be truncated and in some cases arguments to primitive operations to be mixed up. Filenames containing null characters inside the filename are now rejected and will cause primitive file operations to fail.


Currently null characters at the end of the filename will be accepted by primitive file operations. Such filenames are however still documented as invalid. The implementation will also change in the future and reject such filenames.

Data Types

find_file_rule() =
    {ObjDirSuffix :: string(), SrcDirSuffix :: string()}

find_source_rule() =
    {ObjExtension :: string(),
     SrcExtension :: string(),

ensure_dir(Name) -> ok | {error, Reason}


Reason = file:posix()

Ensures that all parent directories for the specified file or directory name Name exist, trying to create them if necessary.

Returns ok if all parent directories already exist or can be created. Returns {error, Reason} if some parent directory does not exist and cannot be created.

file_size(Filename) -> integer() >= 0


Filename = filename_all()

Returns the size of the specified file.

fold_files(Dir, RegExp, Recursive, Fun, AccIn) -> AccOut


Dir = dirname()
RegExp = string()
Recursive = boolean()
Fun = fun((F :: file:filename(), AccIn) -> AccOut)
AccIn = AccOut = term()

Folds function Fun over all (regular) files F in directory Dir that match the regular expression RegExp (for a description of the allowed regular expressions, see the re module). If Recursive is true, all subdirectories to Dir are processed. The regular expression matching is only done on the filename without the directory part.

If Unicode filename translation is in effect and the file system is transparent, filenames that cannot be interpreted as Unicode can be encountered, in which case the fun() must be prepared to handle raw filenames (that is, binaries). If the regular expression contains codepoints > 255, it does not match filenames that do not conform to the expected character encoding (that is, are not encoded in valid UTF-8).

For more information about raw filenames, see the file module.

is_dir(Name) -> boolean()


Returns true if Name refers to a directory, otherwise false.

is_file(Name) -> boolean()


Returns true if Name refers to a file or a directory, otherwise false.

is_regular(Name) -> boolean()


Returns true if Name refers to a (regular) file, otherwise false.

last_modified(Name) -> file:date_time() | 0


Returns the date and time the specified file or directory was last modified, or 0 if the file does not exist.

wildcard(Wildcard) -> [file:filename()]


Wildcard = filename() | dirname()

Returns a list of all files that match Unix-style wildcard string Wildcard.

The wildcard string looks like an ordinary filename, except that the following "wildcard characters" are interpreted in a special way:


Matches one character.


Matches any number of characters up to the end of the filename, the next dot, or the next slash.


Two adjacent * used as a single pattern match all files and zero or more directories and subdirectories.


Matches any of the characters listed. Two characters separated by a hyphen match a range of characters. Example: [A-Z] matches any uppercase letter.


Alternation. Matches one of the alternatives.

Other characters represent themselves. Only filenames that have exactly the same character in the same position match. Matching is case-sensitive, for example, "a" does not match "A".

Directory separators must always be written as /, even on Windows.

A character preceded by \ loses its special meaning. Note that \ must be written as \\ in a string literal. For example, "\\?*" will match any filename starting with ?.

Notice that multiple "*" characters are allowed (as in Unix wildcards, but opposed to Windows/DOS wildcards).


The following examples assume that the current directory is the top of an Erlang/OTP installation.

To find all .beam files in all applications, use the following line:


To find .erl or .hrl in all applications src directories, use either of the following lines:


To find all .hrl files in src or include directories:


To find all .erl or .hrl files in either src or include directories:


To find all .erl or .hrl files in any subdirectory:


wildcard(Wildcard, Cwd) -> [file:filename()]


Wildcard = filename() | dirname()
Cwd = dirname()

Same as wildcard/1, except that Cwd is used instead of the working directory.

find_file(Filename :: filename(), Dir :: filename()) ->
             {ok, filename()} | {error, not_found}
OTP 20.0
find_file(Filename :: filename(),
          Dir :: filename(),
          Rules :: [find_file_rule()]) ->
             {ok, filename()} | {error, not_found}
OTP 20.0

Looks for a file of the given name by applying suffix rules to the given directory path. For example, a rule {"ebin", "src"} means that if the directory path ends with "ebin", the corresponding path ending in "src" should be searched.

If Rules is left out or is an empty list, the default system rules are used. See also the Kernel application parameter source_search_rules.

find_source(FilePath :: filename()) ->
               {ok, filename()} | {error, not_found}
OTP 20.0

Equivalent to find_source(Base, Dir), where Dir is filename:dirname(FilePath) and Base is filename:basename(FilePath).

find_source(Filename :: filename(), Dir :: filename()) ->
               {ok, filename()} | {error, not_found}
OTP 20.0
find_source(Filename :: filename(),
            Dir :: filename(),
            Rules :: [find_source_rule()]) ->
               {ok, filename()} | {error, not_found}
OTP 20.0

Applies file extension specific rules to find the source file for a given object file relative to the object directory. For example, for a file with the extension .beam, the default rule is to look for a file with a corresponding extension .erl by replacing the suffix "ebin" of the object directory path with "src" or "src/*". The file search is done through find_file/3. The directory of the object file is always tried before any other directory specified by the rules.

If Rules is left out or is an empty list, the default system rules are used. See also the Kernel application parameter source_search_rules.

safe_relative_path(Filename, Cwd) -> unsafe | SafeFilename
OTP 23.0


Filename = Cwd = SafeFilename = filename_all()

Sanitizes the relative path by eliminating ".." and "." components to protect against directory traversal attacks. Either returns the sanitized path name, or the atom unsafe if the path is unsafe. The path is considered unsafe in the following circumstances:

  • The path is not relative.

  • A ".." component would climb up above the root of the relative path.

  • A symbolic link in the path points above the root of the relative path.


1> {ok, Cwd} = file:get_cwd().
2> filelib:safe_relative_path("dir/sub_dir/..", Cwd).
3> filelib:safe_relative_path("dir/..", Cwd).
4> filelib:safe_relative_path("dir/../..", Cwd).
5> filelib:safe_relative_path("/abs/path", Cwd).