закодировать двоичный файл (encode a binary file)
Пролог (Prolog)
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.
Имя (Name)
uuencode — encode a binary file
Синопсис (Synopsis)
uuencode [-m] [file] decode_pathname
Описание (Description)
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.1‐2017.
Параметры (Options)
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.
Операнды (Operands)
The following operands shall be supported:
decode_pathname
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.
Стандартный ввод (Stdin)
See the INPUT FILES section.
Входные файлы (Input files)
Input files can be files of any type.
Переменные окружения (Environment variables)
The following environment variables shall affect the execution of
uuencode:
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).
LC_MESSAGES
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.
Асинхронные события (Asynchronous events)
Default.
Стандартный вывод (Stdout)
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:
"====\n"
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:
"end\n"
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
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.
Стандартный вывод сообщений (Stderr)
The standard error shall be used only for diagnostic messages.
Выходные файлы (Output files)
None.
Расширенное описание (Extended description)
None.
Статус выхода (Exit)
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Последствия ошибок (Consequences of errors)
Default.
The following sections are informative.
Использование в приложениях (Application usage)
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.
Примеры (Examples)
None.
Обоснование (Rationale)
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
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.
Будущие направления (Future directions)
None.
Смотри также (See also)
chmod(1p), mailx(1p), uudecode(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
