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 POSIX.1‐2008.

OPTIONS         top

       The uuencode utility shall conform to the Base Definitions volume of
       POSIX.1‐2008, 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 unspecified.

       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.1‐2008, Section 8.2, Internationalization
                 Variables for the precedence of internationalization
                 variables used to determine the values of locale

       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

                 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>

       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

       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

       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>

       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

       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 set.

       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 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

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

       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 standard.

       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.1‐2008, 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, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                        UUENCODE(1P)

Pages that refer to this page: uucp(1p)uudecode(1p)uux(1p)a64l(3p)