fren

File renamer that understands dates - with slugify, Unicode, and CamelCase smarts

fren is a command-line tool for batch-renaming files and directories. It detects dates inside filenames in 17+ formats, converts them to ISO 8601, slugifies the rest of the name, splits CamelCase, normalizes Unicode, and lowercases extensions. It also includes a separate merge command for combining directories with automatic conflict resolution.

Features

• 📅 Date Detection: Recognizes 17+ formats inside filenames (human-readable, ISO, datetime, minute-precision) and rewrites them as ISO 8601
• 🔤 Slugification: Cleans filenames by replacing spaces and punctuation with a single separator (default -)
• 🐫 CamelCase Splitting: WhatsApp becomes Whats-App, JSONFile becomes JSON-File
• 🌍 Unicode Normalization: Strips accents (Bancários -> Bancarios) via NFKC + ASCII transliteration
• 📁 Directory Merging: A separate fren merge command moves files between directories, appending _Copy / _Copy1 / _Copy2 on conflicts
• 🔍 Exclusions: Skip specific paths with -x
• 🙈 Hidden Files: Entries starting with . are skipped automatically
• 🔒 Dry-run by default: fren rename DIR previews; --apply is required to actually rename
• 🎨 Colored output: Files in bright green, directories in bright blue, with the unchanged parent path dimmed
• 📜 Transaction log: Every applied batch is recorded as JSONL under ${XDG_STATE_HOME:-~/.local/state}/fren/log/

Installation

From source:

git clone https://github.com/andreoliwa/fren.git
cd fren
cargo install --path crates/fren-cli

This installs the fren binary to ~/.cargo/bin/.

Commands

fren rename

Rename files and directories with slugify + ISO date detection.

fren rename [OPTIONS] DIRECTORIES...

Options:

• -x, --exclude PATH: Exclude one or more paths (can be repeated)
• --apply: Actually perform the renames (without this, fren only prints what it would do)
• --no-log: Skip writing the transaction log
• --log-dir DIR: Override transaction-log directory

Examples:

# Preview (dry-run is the default)
fren rename ~/Documents/MyFiles

# Actually rename
fren rename --apply ~/Documents/MyFiles

# Multiple directories with exclusions
fren rename --apply -x ~/temp/skip -x ~/temp/important.txt ~/temp

fren merge

Merge source directories into a target directory. Move-only - filenames are preserved (with _Copy suffixes on conflicts). If you also want to rename the merged contents, run fren rename afterwards.

fren merge [OPTIONS] TARGET SOURCES...

Options:

• --apply: Actually perform the moves

Examples:

# Preview
fren merge ~/Documents/Target ~/Documents/Source1 ~/Documents/Source2

# Apply
fren merge --apply ~/Documents/Target ~/Documents/Source1 ~/Documents/Source2

# Merge several into the current directory
fren merge --apply . src1/ src2/ src3/

fren completions

Print shell completions.

fren completions bash > ~/.local/share/bash-completion/completions/fren
fren completions zsh  > ~/.zsh/completions/_fren
fren completions fish > ~/.config/fish/completions/fren.fish

How rename works

The pipeline transforms filenames in this order:

1. Unicode normalize (NFKC) and transliterate non-ASCII to ASCII
2. Inject separator at CamelCase boundaries (WhatsApp -> Whats_App)
3. Inject separator at "at"-time patterns (2019-08-21 at 14.24.19 -> 2019-08-21_14_24_19)
4. Slugify: replace whitespace and punctuation with the internal separator
5. Detect dates and rewrite them as ISO 8601
6. Apply case mode (default: preserve original case)
7. Collapse consecutive separators and substitute to user separator (default -)
8. Lowercase the file extension

Examples

Hello World 2024-01-15.txt           -> Hello-World-2024-01-15.txt
WhatsApp Image 2024-01-15 at 12.30.45.jpg -> Whats-App-Image-2024-01-15T12-30-45.jpg
CamelCaseFile.PDF                    -> Camel-Case-File.pdf
Bancários.txt                        -> Bancarios.txt
report-25-04-2017.pdf                -> report-2017-04-25.pdf
photo_20191020.jpg                   -> photo-2019-10-20.jpg
2026-05-03-18-57.log                 -> 2026-05-03T18-57-00.log

Supported date formats

• Human-readable: DD_MM_YYYY, DD/MM/YYYY, DD.MM.YYYY, DD-MM-YY, DDMMYYYY, DDMMYY, MM_YYYY
• ISO / inverted: YYYY-MM-DD, YYYY_MM_DD, YYYYMMDD, YYYY_MM
• Datetime (full): DD_MM_YYYY_HH_mm_ss, YYYY_MM_DD_HH_mm_ss, YYYYMMDDHHmmss, YYYYMMDD_HHmmss, DD_MM_YY_HH_mm_ss, YY_MM_DD_HH_mm_ss
• Datetime (minute-precision, zero-second pad): DD_MM_YYYY_HH_mm, YYYY_MM_DD_HH_mm, DDMMYYYYHHmm

Two-digit years between (current_year + 10) and 99 are interpreted as 19YY; otherwise 20YY. With the system clock at 2026 this means 30..=99 -> 1930..1999 and 00..=29 -> 2000..2029, except dates more than 10 years in the future, which roll back a century.

How merge works

fren merge TARGET SOURCES...:

1. Walks each source recursively
2. Computes the target path = TARGET / relative_subpath_from_source
3. If the target file already exists (or another move in the batch already claimed that path), appends _Copy, _Copy1, _Copy2, ... to the stem until a free name is found
4. Creates intermediate directories as needed
5. Moves the file with std::fs::rename
6. Skips .DS_Store and similar metadata files

Source directory structure is preserved verbatim. Only files are moved; empty source directories remain.

Architecture

fren is a Cargo workspace with three crates:

• crates/slug-preserve (internal): a case-preserving slugifier. Unlike most Rust slug crates that always lowercase, this one supports five case modes: Preserve, Lower, Upper, Title, Capitalize.
• crates/fren: the library. Exposes slugify_camel_iso, plan, execute, merge_directories, unique_file_name, plus the public type surface (RenamePlan, DetectedDate, FrenError, ConflictPolicy, SlugOpts, LogSink, JsonlLogSink, etc.). No CLI dependencies; library discipline lints deny print_stdout, print_stderr, panic, unwrap_used, expect_used.
• crates/fren-cli: a thin clap-derive binary that consumes the library.

The library is the source of truth. The binary parses arguments, builds option structs, and formats output. Other Rust projects can embed fren directly without spawning a subprocess.

Safety

• Dry-run is the default. --apply is required to mutate the filesystem.
• No silent overwrites. Every rename pre-checks the target and refuses to proceed if it exists outside the batch (the Abort conflict policy).
• Within-batch collisions are detected at planning time. If two source paths would rename to the same target, the batch aborts before any I/O happens.
• Bottom-up execution. Deeper paths are renamed first, so a directory rename never invalidates the queued paths of its children. This fixes a class of bugs that affected the original Python implementation.
• Case-only renames on case-insensitive filesystems (macOS APFS, Windows NTFS) route through a temporary name to avoid silent no-ops.
• Transaction log. Every applied batch writes a JSONL file under ${XDG_STATE_HOME:-~/.local/state}/fren/log/<timestamp>-<batch-uuid>.jsonl so applied changes can be audited or, in the future, undone.

Development

cargo build           # debug build
cargo test            # 48 tests across slugify, planner, executor, merge
cargo clippy --workspace --all-targets -- -D warnings
cargo fmt --all
cargo install --path crates/fren-cli   # install/refresh ~/.cargo/bin/fren

Pre-commit:

prek install
prek run

License

See the project repository for license information.

Author

W. Augusto Andreoli (andreoliwa@sent.com)