# bash-scripts

A collection of Bash utilities. Works on Linux, macOS, WSL, and Git Bash (Windows).

## Scripts

| Script | Purpose |
|---|---|
| [find_duplicate_pictures.sh](find_duplicate_pictures.sh) | Find duplicate pictures across one or more filesystems/directories using name **and** content comparison |

---

## find_duplicate_pictures.sh

Finds all picture files and reports duplicates. Because more than one picture
can legitimately share the same file name (e.g. `IMG_0001.jpg` from two
different cameras), the script does **not** trust names alone — it combines
three independent checks:

1. **Same name** — groups files sharing the same file name (case-insensitive).
   Fast, but only a hint.
2. **Same content** *(authoritative)* — file size is used as a cheap
   pre-filter, then SHA-256 hashes are computed **only for size-matched
   candidates**. Identical hashes = true duplicates, regardless of name.
   Also reports approximate disk space wasted by redundant copies.
3. **"False friends"** — files with the *same name but different content*
   (the exact case where names are misleading).

### Usage

```bash
# Scan specific roots
./find_duplicate_pictures.sh /home/user/Pictures /mnt/backup

# Scan the whole filesystem (default when no arguments given)
./find_duplicate_pictures.sh

# On Windows (Git Bash) — drives are /c, /d, ...
"/c/Program Files/Git/bin/bash.exe" find_duplicate_pictures.sh /c /d

# Make it executable first if needed
chmod +x find_duplicate_pictures.sh
```

### Options (environment variables)

| Variable | Default | Description |
|---|---|---|
| `HASH_CMD` | auto-detected | Hash tool to use: `sha256sum`, `shasum -a 256`, or `md5sum` (last resort) |
| `FOLLOW_LINKS` | `0` (off) | Set to `1` to follow symlinks while scanning |
| `REPORT` | *(none)* | Path to a file where the full report is also saved |

### Examples

```bash
# Save the report to a file
REPORT=dupes.txt ./find_duplicate_pictures.sh ~/Pictures

# Follow symlinks, scan two drives
FOLLOW_LINKS=1 ./find_duplicate_pictures.sh /mnt/c /mnt/d

# Force a specific hash tool
HASH_CMD="shasum -a 256" ./find_duplicate_pictures.sh ~/Pictures
```

### Sample output

```
=== Step 1: scanning for picture files ===
  -> /tmp/picdup_test
  found 3 picture file(s)

=== Step 2: duplicates by file name ===
--- name: photo1.jpg ---
         100 bytes  /tmp/picdup_test/a/photo1.jpg
         120 bytes  /tmp/picdup_test/b/photo1.jpg
  1 name group(s) share the same file name

=== Step 3: duplicates by content (SHA-256) ===
  hashing 2 candidate file(s) with matching sizes...
--- identical content (sha256: 57e8310931615cb7...) ---
         100 bytes  /tmp/picdup_test/a/photo1.jpg
         100 bytes  /tmp/picdup_test/b/copy_of_photo1.jpg
  1 content group(s) are true duplicates
  approx. space wasted by extra copies: 100 bytes (100)

=== Step 4: same name, different content (false friends) ===
--- 'photo1.jpg' is used by 2 DIFFERENT pictures: ---
  [57e831093161] /tmp/picdup_test/a/photo1.jpg
  [unique-size] /tmp/picdup_test/b/photo1.jpg
```

### Supported image formats

`jpg`, `jpeg`, `png`, `gif`, `bmp`, `tiff`, `tif`, `webp`, `heic`, `heif`,
`svg`, `ico`, `raw`, `cr2`, `nef`, `arw`, `dng`, `psd`, `avif`, `jfif`

Matching is case-insensitive (`.JPG`, `.Jpg`, … all match). To change the
list, edit the `EXTENSIONS` variable at the top of the script.

### Notes & limitations

- **Safety:** the script is read-only — it never deletes or modifies files.
- **Skipped paths:** `/proc`, `/sys`, `/dev`, `/run`, `/snap`, `/tmp` are
  pruned during full-system scans (edit `PRUNE_DIRS` to change).
- **Performance:** only files whose size appears more than once are hashed,
  which keeps large collections fast. Whole-filesystem scans still take time.
- **Filenames:** names with spaces, tabs, or other special characters are
  handled correctly (NUL-delimited scanning).
- **Permissions:** unreadable files/directories are skipped silently.
- **Exit codes:** `0` on success; `1` if no hashing tool is available or the
  temp directory cannot be created.

### Requirements

- Bash 4+ (for `mapfile`)
- One of: `sha256sum`, `shasum`, or `md5sum`
- Standard tools: `find`, `awk`, `sort`, `stat`, `cut`, `grep`, `wc`
  (all present on Linux/macOS/Git Bash/WSL)