uuencode - encode a binary file
uuencode [file] decode_pathname
The uuencode utility writes an encoded version of the named input file, or standard input if no file is specified, to standard output. The output is encoded using the algorithm described in the STDOUT section and includes the file access permission bits (in chmod octal or symbolic notation) of the input file and the decode_pathname, for re-creation of the file on another system that conforms to this specification.
The following operands are supported:
- The pathname of the file into which the uudecode utility will place the decoded file. If there are characters in decode_pathname that are not in the portable filename character set the results are unspecified.
- A pathname of the file to be encoded.
See the INPUT FILES section.
Input files can be files of any type.
The following environment variables affect the execution of uuencode:
- Provide a default value for the internationalisation variables that are unset or null. If LANG is unset or null, the corresponding value from the implementation-dependent default locale will be used. If any of the internationalisation variables contains an invalid setting, the utility will behave as if none of the variables had been defined.
- If set to a non-empty string value, override the values of all the other internationalisation variables.
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single- as opposed to multi-byte characters in arguments and input files).
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- Determine the location of message catalogues for the processing of LC_MESSAGES .
The standard output is a text file (encoded in the character set of the current locale) that begins with the line:
"begin%s%s\n", <mode>, decode_pathnameand ends with the line:
In both cases, the lines have no preceding or trailing blank characters.
The algorithm that is used for lines in between begin and end takes three octets as input and writes four characters of output by splitting the input at six-bit intervals into four octets, containing data in the lower six bits only. These octets are converted to characters by adding a value of 0x20 to each octet, so that each octet is in the range 0x20-0x5f, and then it is assumed to represent a printable character in the ISO/IEC 646:1991 standard encoded character set. It then will be translated into the corresponding character codes for the codeset in use in the current locale. (For example, the octet 0x41, representing A, would be translated to A in the current codeset, such as 0xc1 if it were EBCDIC.)
Where the bits of two octets are combined, the least significant bits of the first octet are shifted left and combined with the most significant bits of the second octet shifted right. Thus the three octets A, B, C are converted into the four octets:These octets are then translated into the local character set.
0x20 + (( A >> 2 ) & 0x3F) 0x20 + (((A << 4) ' |' ((B >> 4) & 0xF)) & 0x3F) 0x20 + (((B << 2) ' |' ((C >> 6) & 0x3)) & 0x3F) 0x20 + (( C ) & 0x3F)
Each encoded line contains a length character, equal to the number of characters to be decoded plus 0x20 translated to the local character set as described above, followed by the encoded characters. The maximum number of octets to be encoded on each line is 45.
Used only for diagnostic messages.
The following exit values are returned:
- Successful completion.
- An error occurred.
The file is expanded by 35 percent (each three octets become four, plus control information) causing it to take longer to transmit.
Since this utility is intended to create files to be used for data interchange between systems with possibly different codesets, and to represent binary data as a text file, the ISO/IEC 646:1991 standard was chosen for a midpoint in the algorithm as a known reference point. The output from uuencode is a text file on the local system. If the output were in the ISO/IEC 646:1991 standard codeset, it might not be a text file (at least because the newline characters might not match), and the goal of creating a text file would be defeated. If this text file was then carried to another machine with the same codeset, it would be perfectly compatible with that system's uudecode. If it was transmitted over a mail system or sent to a machine with a different codeset, it is assumed that, as for every other text file, some translation mechanism would convert it (by the time it reached a user on the other system) into an appropriate codeset. This translation only makes sense from the local codeset, not if the file has been put into a ISO/IEC 646:1991 standard representation first. Similarly, files processed by uuencode can be placed in pax archives, intermixed with other text files in the same codeset.
The algorithm is described in terms of 8-bit quantities, or octets. Since no byte alignment is implied, it will encode data from machines with any number of bits per byte. However, unless that encoded data is then decoded on a machine with the same number of bits per byte, the output might not be useful.