LinuxWhat is the UUE file format?
A .uue file is a text-encoded representation of binary data, produced by the uuencode utility first bundled with BSD 4.0 Unix around 1980. The name stands for Unix-to-Unix Encoding, reflecting its original role transferring binary files over text-only connections and Usenet.
Every .uue file follows a fixed three-part structure: a header line in the form begin <unix-permissions> <filename> (for example begin 644 archive.zip), one or more data lines, and a final end line. The encoding maps every 3 bytes of binary input to four 6-bit groups, adds 32 to each group, and produces printable ASCII characters in the range 0x20 (space) to 0x5F (underscore). Each data line holds up to 60 encoded characters, representing 45 raw bytes. A common variant substitutes a backtick for the space character to avoid whitespace stripping on mail servers. This overhead increases the output by roughly 33-40% compared to the original binary.
UUencoding dominated binary sharing on Usenet throughout the 1980s and 1990s. Large files were split into multi-part posts, each a self-contained .uu or .uue segment. The format carries no built-in checksum, though some implementations append a CRC or MD5 comment.
By the mid-1990s, Base64 (RFC 2045) overtook UUencoding for email attachments, and yEnc largely replaced it on Usenet after 2001. Encountering a .uue file today typically means a legacy Usenet archive or a very old email attachment. Tools such as WinRAR, 7-Zip, and the command-line uudecode utility can still decode them.
Security & safety
RISK: MEDIUMThe .uue file itself is harmless ASCII text. The EMBEDDED binary may be an executable, archive with malware, or other dangerous content. Always scan the decoded output before opening it. The UUE encoding provides no integrity check - a corrupt or tampered file will decode without error warnings in basic tools.
Format details
in a nutshellPrograms that open UUE files
Windows4 apps
WinZip
Paid Open the .uue file in WinZip; it decodes UUE natively and shows the contained file for extraction. 
WinRAR
Freemium Right-click .uue → Open with WinRAR → Extract Here. WinRAR decodes and extracts the embedded file automatically. 
macOS2 apps
The Unarchiver
Free Double-click the .uue file; The Unarchiver decodes it and places the result in the same folder. 
uudecode (command line)
Built-in Terminal: uudecode filename.uue - outputs the decoded file named per the 'begin' header. Technical details
deep spec| Encoding algorithm | Every 3 binary bytes split into four 6-bit groups; each group + 32 → printable ASCII (`0x20`-`0x5F`) |
| Header line format | `begin <octal-permissions> <filename>` - e.g. `begin 644 archive.zip` |
| Footer line | Single line containing the word `end` |
| Data line capacity | Up to 60 encoded characters per line, representing 45 raw bytes |
| Size overhead | ~33-40% larger than the original binary payload |
| MIME type | `text/x-uuencode`; binary payloads also served as `application/octet-stream` |
| Character set | Printable 7-bit ASCII only, range `0x20` (space) to `0x5F` (underscore) |
| Zero-value variant | Backtick substituted for space (`0x20`) in some implementations to survive mail-server whitespace stripping |
| Unix permissions field | Octal mode (e.g. `644`) embedded in the `begin` header line, restored on decode |
| Multi-part support | Large Usenet payloads split across sequential posts; each part is a self-contained `.uue` segment |
| Integrity check | None in base format; some implementations append a CRC or MD5 checksum in a trailing comment line |
| POSIX specification | `uuencode` and `uudecode` utilities defined in POSIX.1-2017 |
| Text encoding | Pure 7-bit ASCII; safely transmitted over any 7-bit clean channel or mail relay |
| Superseded by | MIME Base64 (RFC 2045, 1996) for email; yEnc (2001) for Usenet binary distribution |
| Released | circa 1980 (BSD 4.0 Unix) |
| Latest version | No versioned standard; POSIX.1-2017 defines uuencode/uudecode utilities |
| Open standard | Yes · royalty-free |
| Specification | pubs.opengroup.org |
UUE conversions
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