ffs: the file filesystem

ffs, the file filesystem, let's you mount semi-structured data as a filesystem---a tree structure you already know how to work with!

Working with semi-structured data using command-line tools is hard. Tools like jq help a lot, but learning a new language for simple manipulations is a big ask. By mapping hard-to-parse trees into a filesystem, you can keep using the tools you know.

Example

Run ffs [file.blah] to mount file.blah at the mountpoint file. The final, updated version of the file will be outputted on stdout.

$ cat object.json
{ "name": "Michael Greenberg", "eyes": 2, "fingernails": 10, "human": true }
$ ffs -o object_edited.json object.json &
[1] 60182
$ tree object
object
├── eyes
├── fingernails
├── human
└── name

0 directories, 4 files
$ echo Mikey Indiana >object/name
$ echo 1 >object/nose
$ mkdir object/pockets
$ cd object/pockets/
$ echo keys >pants
$ echo pen >shirt
$ cd ..
$ cd ..
$ umount object
$
[1]+  Done                    ffs -o object_edited.json object.json
$ cat object_edited.json
{"eyes":2,"fingernails":10,"human":true,"name":"Mikey Indiana","nose":1,"pockets":{"pants":"keys","shirt":"pen"}}

You can specify an explicit mountpoint by running ffs -m MOUNT file; you can specify an output file with -o OUTPUT. You can edit a file in place by running ffs -i file---when the volume is unmounted, the resulting output will be written back to file.

You can control whether directories are rendered as objects or arrays lists using extended file attributes (xattrs): the user.type xattr specifies named for objects and list for arrays. Here, we create a new JSON file and use Linux's setfattr to mark a directory as being a list:

~$ ffs --new l.json &
[1] 287077
~$ cd l
~/l $ echo 'hi' >a
~/l $ echo 'bye' >b
~/l $ echo 'hello' >a1
~/l $ ls
a  a1  b
~/l $ cd ..
~$ setfattr -n user.type -v list l
~$ umount l
[1]+  Done                    ffs --new l.json
~$ cat l.json
["hi","hello","bye"]

External dependencies

You need an appropriate FUSE along with pkg-config.

See the GitHub build workflow for examples of external dependency installation.

pack/unpack

ffs only works on Linux, using FUSE to make a synthetic filesystem.

The pack/unpack tools in this repository work differently: they turn filesystems into semi-structured data (pack) and semi-structured data into files (unpack). These tools should work on any POSIX platform, and are currently in a prerelease/beta state.