uuencode(1p) — Linux manual page


UUENCODE(1P)            POSIX Programmer's Manual           UUENCODE(1P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       uuencode — encode a binary file

SYNOPSIS         top

       uuencode [-m] [file] decode_pathname

DESCRIPTION         top

       The uuencode utility shall write an encoded version of the named
       input file, or standard input if no file is specified, to
       standard output. The output shall be encoded using one of the
       algorithms described in the STDOUT section and shall include 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 volume of

OPTIONS         top

       The uuencode utility shall conform to the Base Definitions volume
       of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.

       The following option shall be supported by the implementation:

       -m        Encode the output using the MIME Base64 algorithm
                 described in STDOUT.  If -m is not specified, the
                 historical algorithm described in STDOUT shall be used.

OPERANDS         top

       The following operands shall be supported:

                 The pathname of the file into which the uudecode
                 utility shall place the decoded file. Specifying a
                 decode_pathname operand of /dev/stdout shall indicate
                 that uudecode is to use standard output. If there are
                 characters in decode_pathname that are not in the
                 portable filename character set the results are

       file      A pathname of the file to be encoded.

STDIN         top

       See the INPUT FILES section.

INPUT FILES         top

       Input files can be files of any type.


       The following environment variables shall affect the execution of

       LANG      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base
                 Definitions volume of POSIX.1‐2017, Section 8.2,
                 Internationalization Variables for the precedence of
                 internationalization variables used to determine the
                 values of locale categories.)

       LC_ALL    If set to a non-empty string value, override the values
                 of all the other internationalization variables.

       LC_CTYPE  Determine the locale for the interpretation of
                 sequences of bytes of text data as characters (for
                 example, single-byte 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.

       NLSPATH   Determine the location of message catalogs for the
                 processing of LC_MESSAGES.



STDOUT         top

   uuencode Base64 Algorithm
       The standard output shall be a text file (encoded in the
       character set of the current locale) that begins with the line:

           "begin-base64 %s %s\n", <mode>, <decode_pathname>

       and ends with the line:


       In both cases, the lines shall have no preceding or trailing
       <blank> characters.

       The encoding process represents 24-bit groups of input bits as
       output strings of four encoded characters. Proceeding from left
       to right, a 24-bit input group shall be formed by concatenating
       three 8-bit input groups. Each 24-bit input group then shall be
       treated as four concatenated 6-bit groups, each of which shall be
       translated into a single digit in the Base64 alphabet. When
       encoding a bit stream via the Base64 encoding, the bit stream
       shall be presumed to be ordered with the most-significant bit
       first. That is, the first bit in the stream shall be the high-
       order bit in the first byte, and the eighth bit shall be the low-
       order bit in the first byte, and so on. Each 6-bit group is used
       as an index into an array of 64 printable characters, as shown in
       Table 4-22, uuencode Base64 Values.

                      Table 4-22: uuencode Base64 Values

  │Value Encoding ││Value Encoding ││Value Encoding ││Value Encoding │
  │  0   │    A     ││ 17   │    R     ││ 34   │    i     ││ 51   │    z     │
  │  1   │    B     ││ 18   │    S     ││ 35   │    j     ││ 52   │    0     │
  │  2   │    C     ││ 19   │    T     ││ 36   │    k     ││ 53   │    1     │
  │  3   │    D     ││ 20   │    U     ││ 37   │    l     ││ 54   │    2     │
  │  4   │    E     ││ 21   │    V     ││ 38   │    m     ││ 55   │    3     │
  │  5   │    F     ││ 22   │    W     ││ 39   │    n     ││ 56   │    4     │
  │  6   │    G     ││ 23   │    X     ││ 40   │    o     ││ 57   │    5     │
  │  7   │    H     ││ 24   │    Y     ││ 41   │    p     ││ 58   │    6     │
  │  8   │    I     ││ 25   │    Z     ││ 42   │    q     ││ 59   │    7     │
  │  9   │    J     ││ 26   │    a     ││ 43   │    r     ││ 60   │    8     │
  │ 10   │    K     ││ 27   │    b     ││ 44   │    s     ││ 61   │    9     │
  │ 11   │    L     ││ 28   │    c     ││ 45   │    t     ││ 62   │    +     │
  │ 12   │    M     ││ 29   │    d     ││ 46   │    u     ││ 63   │    /     │
  │ 13   │    N     ││ 30   │    e     ││ 47   │    v     ││      │          │
  │ 14   │    O     ││ 31   │    f     ││ 48   │    w     ││(pad) │    =     │
  │ 15   │    P     ││ 32   │    g     ││ 49   │    x     ││      │          │
  │ 16   │    Q     ││ 33   │    h     ││ 50   │    y     ││      │          │
       The character referenced by the index shall be placed in the
       output string.

       The output stream (encoded bytes) shall be represented in lines
       of no more than 76 characters each. All line breaks or other
       characters not found in the table shall be ignored by decoding
       software (see uudecode(1p)).

       Special processing shall be performed if fewer than 24 bits are
       available at the end of a message or encapsulated part of a
       message. A full encoding quantum shall always be completed at the
       end of a message. When fewer than 24 input bits are available in
       an input group, zero bits shall be added (on the right) to form
       an integral number of 6-bit groups. Output character positions
       that are not required to represent actual input data shall be set
       to the character '='.  Since all Base64 input is an integral
       number of octets, only the following cases can arise:

        1. The final quantum of encoding input is an integral multiple
           of 24 bits; here, the final unit of encoded output shall be
           an integral multiple of 4 characters with no '=' padding.

        2. The final quantum of encoding input is exactly 16 bits; here,
           the final unit of encoded output shall be three characters
           followed by one '=' padding character.

        3. The final quantum of encoding input is exactly 8 bits; here,
           the final unit of encoded output shall be two characters
           followed by two '=' padding characters.

       A terminating "====" evaluates to nothing and denotes the end of
       the encoded data.

   uuencode Historical Algorithm
       The standard output shall be a text file (encoded in the
       character set of the current locale) that begins with the line:

           "begin %s %s\n" <mode>, <decode_pathname>

       and ends with the line:


       In both cases, the lines shall have no preceding or trailing
       <blank> characters.

       The algorithm that shall be 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
       shall be 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 shall be assumed to represent a printable character in
       the ISO/IEC 646:1991 standard encoded character set. It then
       shall 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 shall be shifted left and combined with
       the most significant bits of the second octet shifted right. Thus
       the three octets A, B, C shall be converted into the four octets:

           0x20 + (( A >> 2                    ) & 0x3F)
           0x20 + (((A << 4) | ((B >> 4) & 0xF)) & 0x3F)
           0x20 + (((B << 2) | ((C >> 6) & 0x3)) & 0x3F)
           0x20 + (( C                         ) & 0x3F)

       These octets then shall be translated into the local character

       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 shall be 45.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top




EXIT STATUS         top

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.



       The following sections are informative.


       The file is expanded by 35 percent (each three octets become
       four, plus control information) causing it to take longer to

       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.

EXAMPLES         top


RATIONALE         top

       A new algorithm was added at the request of the international
       community to parallel work in RFC 2045 (MIME). As with the
       historical uuencode format, the Base64 Content-Transfer-Encoding
       is designed to represent arbitrary sequences of octets in a form
       that is not humanly readable. A 65-character subset of the
       ISO/IEC 646:1991 standard is used, enabling 6 bits to be
       represented per printable character. (The extra 65th character,
       '=', is used to signify a special processing function.)

       This subset has the important property that it is represented
       identically in all versions of the ISO/IEC 646:1991 standard,
       including US ASCII, and all characters in the subset are also
       represented identically in all versions of EBCDIC. The historical
       uuencode algorithm does not share this property, which is the
       reason that a second algorithm was added to the ISO POSIX‐2

       The string "====" was used for the termination instead of the end
       used in the original format because the latter is a string that
       could be valid encoded input.

       In an early draft, the -m option was named -b (for Base64), but
       it was renamed to reflect its relationship to the RFC 2045. A -u
       was also present to invoke the default algorithm, but since this
       was not historical practice, it was omitted as being unnecessary.

       See the RATIONALE section in uudecode(1p) for the derivation of
       the /dev/stdout symbol.



SEE ALSO         top

       chmod(1p), mailx(1p), uudecode(1p)

       The Base Definitions volume of POSIX.1‐2017, Chapter 8,
       Environment Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                      UUENCODE(1P)

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