UUEncode Encode/Decode
Online UUEncode encoder and decoder with bidirectional conversion between plain text and UU data, including optional begin/end header, filename and mode settings
Encode Options
UUEncode Format Guide
UUEncode (Unix-to-Unix Encode) is a legacy encoding method that maps binary data to printable ASCII text, commonly seen in old email and Usenet transfers.
What is UUEncode
It splits every 3 bytes into 4 groups of 6 bits, then maps them to ASCII 32-95 for text-only transport channels.
Format Structure
Optional begin MODE filename header, body lines encoded from up to 45 bytes each, and usually a ` line plus end.
Length Character
The first character of each line indicates original byte count (value+32); backtick often represents zero-byte end line.
Compatibility Tip
Use Base64 for modern projects; use UUEncode mainly for legacy email archives and old systems.
UUEncode Character Set
UUEncode uses 64 continuous ASCII chars (0-63 mapped to ASCII 32-95):
- Values 0-31: space and common punctuation
- Values 32-63: at sign, A-Z, [ \ ], ^, _
Note: value 0 may appear as space (SP) or backtick (`), depending on implementation.
UUEncode vs Base64
| Feature | UUEncode | Base64 |
|---|---|---|
| Character set | SP-_ (ASCII 32-95) | A-Za-z0-9+/ |
| Max bytes per line | 45 bytes | No strict limit (MIME often wraps) |
| Header/Footer | begin/end | Usually none |
| Current usage | Mostly legacy | Widely used |
Common Scenarios
- Decode legacy UUEncode data from old email or Usenet archives
- Handle UU text exported by old systems
- Troubleshoot compatibility issues in historical pipelines
- Learn classic text encoding algorithms