Uudecode

Uuencoding is a form of binary-to-text encoding that originated in the Unix programs uuencode and uudecode written by Mary Ann Horton at UC Berkeley in 1980, for encoding binary data for transmission in email systems.

The name "uuencoding" is derived from "Unix-to-Unix encoding", i.e. the idea of using a safe encoding to transfer Unix files from one Unix system to another Unix system but without guarantee that the intervening links would all be Unix systems. Since an email message might be forwarded through or to computers with different character sets or through transports which are not 8-bit clean, or handled by programs that are not 8-bit clean; forwarding a binary file via email might cause it to be corrupted. By encoding such data into a character subset common to most character sets, the encoded form of such data files was unlikely to be "translated" or corrupted, and would thus arrive intact and unchanged at the destination. The program uudecode reverses the effect of uuencode, recreating the original binary file exactly. uuencode/decode became popular for sending binary (and especially compressed) files by e-mail and posting to Usenet newsgroups, etc.

It has now been largely replaced by MIME and yEnc. With MIME, files that might have been uuencoded are instead transferred with base64 encoding.

A uuencoded file starts with a header line of the form:

<mode> is the file's Unix file permissions as three octal digits (e.g. 644, 744). This is typically only significant to unix-like operating systems.

<file> is the file name to be used when recreating the binary data.

<newline> signifies a newline character, used to terminate each line.

Each data line uses the format:

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