File utilities, such as wildcard matching of filenames

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

The module supports Unicode file names, so that it will match against regular expressions given in Unicode and that it will find and process raw file names (i.e. files named in a way that does not confirm to the expected encoding).

If the VM operates in Unicode file naming mode on a machine with transparent file naming, the fun() provided to fold_files/5 needs to be prepared to handle binary file names.

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


filename() = string() | atom() | DeepList | RawFilename
  DeepList = [char() | atom() | DeepList]
  RawFilename = binary()
  If VM is in unicode filename mode, string() and char() are allowed to be > 255.
  RawFilename is a filename not subject to Unicode translation, meaning that it 
  can contain characters not conforming to the Unicode encoding expected from the 
  filesystem (i.e. non-UTF-8 characters although the VM is started in Unicode 
  filename mode).
dirname() = filename()


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

  • Name = filename() | dirname()
  • Reason = posix() -- see file(3)

The ensure_dir/1 function ensures that all parent directories for the given file or directory name Name exist, trying to create them if necessary.

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

file_size(Filename) -> integer()

The file_size function returns the size of the given file.

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

  • Dir = dirname()
  • RegExp = regular_expression_string()
  • Recursive = true|false
  • Fun = fun(F, AccIn) -> AccOut
  • AccIn = AccOut = term()

The fold_files/5 function folds the function Fun over all (regular) files F in the directory Dir that match the regular expression RegExp (see the re module for a description of the allowed regular expressions). If Recursive is true all sub-directories to Dir are processed. The regular expression matching is done on just the filename without the directory part.

If Unicode file name translation is in effect and the file system is completely transparent, file names that cannot be interpreted as Unicode may be encountered, in which case the fun() must be prepared to handle raw file names (i.e. binaries). If the regular expression contains codepoints beyond 255, it will not match file names that do not conform to the expected character encoding (i.e. are not encoded in valid UTF-8).

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

is_dir(Name) -> true | false

  • Name = filename() | dirname()

The is_dir/1 function returns true if Name refers to a directory, and false otherwise.

is_file(Name) -> true | false

  • Name = filename() | dirname()

The is_file/1 function returns true if Name refers to a file or a directory, and false otherwise.

is_regular(Name) -> true | false

  • Name = filename()

The is_regular/1 function returns true if Name refers to a file (regular file), and false otherwise.

last_modified(Name) -> {{Year,Month,Day},{Hour,Min,Sec}} | 0

  • Name = filename() | dirname()

The last_modified/1 function returns the date and time the given file or directory was last modified, or 0 if the file does not exist.

wildcard(Wildcard) -> list()

  • Wildcard = filename() | dirname()

The wildcard/1 function returns a list of all files that match Unix-style wildcard-string Wildcard.

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


Matches one character.


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


Matches any of the characters listed. Two characters separated by a hyphen will match a range of characters. Example: [A-Z] will match 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 will match. (Matching is case-sensitive; i.e. "a" will not match "A").

Note 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, the following line can be used:


To find either .erl or .hrl in all applications src directories, the following


or the following line


can be used.

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


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


wildcard(Wildcard, Cwd) -> list()

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

The wildcard/2 function works like wildcard/1, except that instead of the actual working directory, Cwd will be used.

View Functions