FileSystemMap
gives an association whose keys are the names of files in root, and whose values are the results of applying f to the full names of these files.
gives a nested association in which subdirectories down to level n are represented by an association.
gives a nested association including files in subdirectories from level m down through n.
Details and Options

- The following options can be given:
-
IncludeDirectories False whether to return f[directory] FileNameForms All include files with names of the specified forms MaxItems Infinity maximum items to include from a directory - FileNameForms will accept any forms specification allowed in the first argument of FileNames.
Examples
open allclose allBasic Examples (3)Summary of the most common use cases
Apply FileSize to all files contained in a directory:

https://wolfram.com/xid/0b0kmowjc8o-5k7wdg

https://wolfram.com/xid/0b0kmowjc8o-ffv41m


https://wolfram.com/xid/0b0kmowjc8o-8ns35m
Apply FileHash to all files through level 2 of the specified directory:

https://wolfram.com/xid/0b0kmowjc8o-if0d7t

Apply FileDate to only those files at level 2 of the specified directory:

https://wolfram.com/xid/0b0kmowjc8o-gwj291

Get a flat association for the same directory:

https://wolfram.com/xid/0b0kmowjc8o-hjo3pe

Options (2)Common values & functionality for each option
FileNameForms (1)
By default, all files are included:

https://wolfram.com/xid/0b0kmowjc8o-d6622f

By specifying FileNameForms->patt, function application will be restricted to only those files that match the specified pattern:

https://wolfram.com/xid/0b0kmowjc8o-bbgyi5

MaxItems (1)
By default, f will be applied to all files in the specified directory and subdirectories:

https://wolfram.com/xid/0b0kmowjc8o-f104x

By specifying MaxItems -> n, f will be applied to at most n items within each directory:

https://wolfram.com/xid/0b0kmowjc8o-bd8a5e

Possible Issues (1)Common pitfalls and unexpected behavior
Wolfram Research (2016), FileSystemMap, Wolfram Language function, https://reference.wolfram.com/language/ref/FileSystemMap.html (updated 2019).
Text
Wolfram Research (2016), FileSystemMap, Wolfram Language function, https://reference.wolfram.com/language/ref/FileSystemMap.html (updated 2019).
Wolfram Research (2016), FileSystemMap, Wolfram Language function, https://reference.wolfram.com/language/ref/FileSystemMap.html (updated 2019).
CMS
Wolfram Language. 2016. "FileSystemMap." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2019. https://reference.wolfram.com/language/ref/FileSystemMap.html.
Wolfram Language. 2016. "FileSystemMap." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2019. https://reference.wolfram.com/language/ref/FileSystemMap.html.
APA
Wolfram Language. (2016). FileSystemMap. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/FileSystemMap.html
Wolfram Language. (2016). FileSystemMap. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/FileSystemMap.html
BibTeX
@misc{reference.wolfram_2025_filesystemmap, author="Wolfram Research", title="{FileSystemMap}", year="2019", howpublished="\url{https://reference.wolfram.com/language/ref/FileSystemMap.html}", note=[Accessed: 19-June-2025
]}
BibLaTeX
@online{reference.wolfram_2025_filesystemmap, organization={Wolfram Research}, title={FileSystemMap}, year={2019}, url={https://reference.wolfram.com/language/ref/FileSystemMap.html}, note=[Accessed: 19-June-2025
]}