1UUENCODE(1P) POSIX Programmer's Manual UUENCODE(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 uuencode — encode a binary file
13
15 uuencode [-m] [file] decode_pathname
16
18 The uuencode utility shall write an encoded version of the named input
19 file, or standard input if no file is specified, to standard output.
20 The output shall be encoded using one of the algorithms described in
21 the STDOUT section and shall include the file access permission bits
22 (in chmod octal or symbolic notation) of the input file and the
23 decode_pathname, for re-creation of the file on another system that
24 conforms to this volume of POSIX.1‐2017.
25
27 The uuencode utility shall conform to the Base Definitions volume of
28 POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
29 The following option shall be supported by the implementation:
31 -m Encode the output using the MIME Base64 algorithm described
33 in STDOUT. If -m is not specified, the historical algorithm
34 described in STDOUT shall be used.
35
37 The following operands shall be supported:
38 decode_pathname
40 The pathname of the file into which the uudecode utility
41 shall place the decoded file. Specifying a decode_pathname
42 operand of /dev/stdout shall indicate that uudecode is to use
43 standard output. If there are characters in decode_pathname
44 that are not in the portable filename character set the
45 results are unspecified.
46 file A pathname of the file to be encoded.
48
50 See the INPUT FILES section.
51
53 Input files can be files of any type.
54
56 The following environment variables shall affect the execution of uuen‐
57 code:
58 LANG Provide a default value for the internationalization vari‐
60 ables that are unset or null. (See the Base Definitions vol‐
61 ume of POSIX.1‐2017, Section 8.2, Internationalization Vari‐
62 ables for the precedence of internationalization variables
63 used to determine the values of locale categories.)
64 LC_ALL If set to a non-empty string value, override the values of
66 all the other internationalization variables.
67 LC_CTYPE Determine the locale for the interpretation of sequences of
69 bytes of text data as characters (for example, single-byte as
70 opposed to multi-byte characters in arguments and input
71 files).
72 LC_MESSAGES
74 Determine the locale that should be used to affect the format
75 and contents of diagnostic messages written to standard
76 error.
77 NLSPATH Determine the location of message catalogs for the processing
79 of LC_MESSAGES.
80
82 Default.
83
85 uuencode Base64 Algorithm
86 The standard output shall be a text file (encoded in the character set
87 of the current locale) that begins with the line:
88 "begin-base64 %s %s\n", <mode>, <decode_pathname>
91 and ends with the line:
93 "====\n"
96 In both cases, the lines shall have no preceding or trailing <blank>
98 characters.
99 The encoding process represents 24-bit groups of input bits as output
101 strings of four encoded characters. Proceeding from left to right, a
102 24-bit input group shall be formed by concatenating three 8-bit input
103 groups. Each 24-bit input group then shall be treated as four concate‐
104 nated 6-bit groups, each of which shall be translated into a single
105 digit in the Base64 alphabet. When encoding a bit stream via the Base64
106 encoding, the bit stream shall be presumed to be ordered with the most-
107 significant bit first. That is, the first bit in the stream shall be
108 the high-order bit in the first byte, and the eighth bit shall be the
109 low-order bit in the first byte, and so on. Each 6-bit group is used as
110 an index into an array of 64 printable characters, as shown in Table
111 4-22, uuencode Base64 Values.
112 Table 4-22: uuencode Base64 Values
114 ┌──────┬──────────┬┬──────┬──────────┬┬──────┬──────────┬┬──────┬──────────┐
116 │Value │ Encoding ││Value │ Encoding ││Value │ Encoding ││Value │ Encoding │
117 ├──────┼──────────┼┼──────┼──────────┼┼──────┼──────────┼┼──────┼──────────┤
118 │ 0 │ A ││ 17 │ R ││ 34 │ i ││ 51 │ z │
119 │ 1 │ B ││ 18 │ S ││ 35 │ j ││ 52 │ 0 │
120 │ 2 │ C ││ 19 │ T ││ 36 │ k ││ 53 │ 1 │
121 │ 3 │ D ││ 20 │ U ││ 37 │ l ││ 54 │ 2 │
122 │ 4 │ E ││ 21 │ V ││ 38 │ m ││ 55 │ 3 │
123 │ 5 │ F ││ 22 │ W ││ 39 │ n ││ 56 │ 4 │
124 │ 6 │ G ││ 23 │ X ││ 40 │ o ││ 57 │ 5 │
125 │ 7 │ H ││ 24 │ Y ││ 41 │ p ││ 58 │ 6 │
126 │ 8 │ I ││ 25 │ Z ││ 42 │ q ││ 59 │ 7 │
127 │ 9 │ J ││ 26 │ a ││ 43 │ r ││ 60 │ 8 │
128 │ 10 │ K ││ 27 │ b ││ 44 │ s ││ 61 │ 9 │
129 │ 11 │ L ││ 28 │ c ││ 45 │ t ││ 62 │ + │
130 │ 12 │ M ││ 29 │ d ││ 46 │ u ││ 63 │ / │
131 │ 13 │ N ││ 30 │ e ││ 47 │ v ││ │ │
132 │ 14 │ O ││ 31 │ f ││ 48 │ w ││(pad) │ = │
133 │ 15 │ P ││ 32 │ g ││ 49 │ x ││ │ │
134 │ 16 │ Q ││ 33 │ h ││ 50 │ y ││ │ │
135 └──────┴──────────┴┴──────┴──────────┴┴──────┴──────────┴┴──────┴──────────┘
136 The character referenced by the index shall be placed in the output
137 string.
138 The output stream (encoded bytes) shall be represented in lines of no
140 more than 76 characters each. All line breaks or other characters not
141 found in the table shall be ignored by decoding software (see uude‐
142 code).
143 Special processing shall be performed if fewer than 24 bits are avail‐
145 able at the end of a message or encapsulated part of a message. A full
146 encoding quantum shall always be completed at the end of a message.
147 When fewer than 24 input bits are available in an input group, zero
148 bits shall be added (on the right) to form an integral number of 6-bit
149 groups. Output character positions that are not required to represent
150 actual input data shall be set to the character '='. Since all Base64
151 input is an integral number of octets, only the following cases can
152 arise:
153 1. The final quantum of encoding input is an integral multiple of 24
155 bits; here, the final unit of encoded output shall be an integral
156 multiple of 4 characters with no '=' padding.
157 2. The final quantum of encoding input is exactly 16 bits; here, the
159 final unit of encoded output shall be three characters followed by
160 one '=' padding character.
161 3. The final quantum of encoding input is exactly 8 bits; here, the
163 final unit of encoded output shall be two characters followed by
164 two '=' padding characters.
165 A terminating "====" evaluates to nothing and denotes the end of the
167 encoded data.
168 uuencode Historical Algorithm
170 The standard output shall be a text file (encoded in the character set
171 of the current locale) that begins with the line:
172 "begin %s %s\n" <mode>, <decode_pathname>
175 and ends with the line:
177 "end\n"
180 In both cases, the lines shall have no preceding or trailing <blank>
182 characters.
183 The algorithm that shall be used for lines in between begin and end
185 takes three octets as input and writes four characters of output by
186 splitting the input at six-bit intervals into four octets, containing
187 data in the lower six bits only. These octets shall be converted to
188 characters by adding a value of 0x20 to each octet, so that each octet
189 is in the range [0x20,0x5f], and then it shall be assumed to represent
190 a printable character in the ISO/IEC 646:1991 standard encoded charac‐
191 ter set. It then shall be translated into the corresponding character
192 codes for the codeset in use in the current locale. (For example, the
193 octet 0x41, representing 'A', would be translated to 'A' in the current
194 codeset, such as 0xc1 if it were EBCDIC.)
195 Where the bits of two octets are combined, the least significant bits
197 of the first octet shall be shifted left and combined with the most
198 significant bits of the second octet shifted right. Thus the three
199 octets A, B, C shall be converted into the four octets:
200 0x20 + (( A >> 2 ) & 0x3F)
203 0x20 + (((A << 4) | ((B >> 4) & 0xF)) & 0x3F)
204 0x20 + (((B << 2) | ((C >> 6) & 0x3)) & 0x3F)
205 0x20 + (( C ) & 0x3F)
206 These octets then shall be translated into the local character set.
208 Each encoded line contains a length character, equal to the number of
210 characters to be decoded plus 0x20 translated to the local character
211 set as described above, followed by the encoded characters. The maximum
212 number of octets to be encoded on each line shall be 45.
213
215 The standard error shall be used only for diagnostic messages.
216
218 None.
219
221 None.
222
224 The following exit values shall be returned:
225 0 Successful completion.
227 >0 An error occurred.
229
231 Default.
232 The following sections are informative.
234
236 The file is expanded by 35 percent (each three octets become four, plus
237 control information) causing it to take longer to transmit.
238 Since this utility is intended to create files to be used for data
240 interchange between systems with possibly different codesets, and to
241 represent binary data as a text file, the ISO/IEC 646:1991 standard was
242 chosen for a midpoint in the algorithm as a known reference point. The
243 output from uuencode is a text file on the local system. If the output
244 were in the ISO/IEC 646:1991 standard codeset, it might not be a text
245 file (at least because the <newline> characters might not match), and
246 the goal of creating a text file would be defeated. If this text file
247 was then carried to another machine with the same codeset, it would be
248 perfectly compatible with that system's uudecode. If it was transmit‐
249 ted over a mail system or sent to a machine with a different codeset,
250 it is assumed that, as for every other text file, some translation
251 mechanism would convert it (by the time it reached a user on the other
252 system) into an appropriate codeset. This translation only makes sense
253 from the local codeset, not if the file has been put into a
254 ISO/IEC 646:1991 standard representation first. Similarly, files pro‐
255 cessed by uuencode can be placed in pax archives, intermixed with other
256 text files in the same codeset.
257
259 None.
260
262 A new algorithm was added at the request of the international community
263 to parallel work in RFC 2045 (MIME). As with the historical uuencode
264 format, the Base64 Content-Transfer-Encoding is designed to represent
265 arbitrary sequences of octets in a form that is not humanly readable. A
266 65-character subset of the ISO/IEC 646:1991 standard is used, enabling
267 6 bits to be represented per printable character. (The extra 65th char‐
268 acter, '=', is used to signify a special processing function.)
269 This subset has the important property that it is represented identi‐
271 cally in all versions of the ISO/IEC 646:1991 standard, including US
272 ASCII, and all characters in the subset are also represented identi‐
273 cally in all versions of EBCDIC. The historical uuencode algorithm does
274 not share this property, which is the reason that a second algorithm
275 was added to the ISO POSIX‐2 standard.
276 The string "====" was used for the termination instead of the end used
278 in the original format because the latter is a string that could be
279 valid encoded input.
280 In an early draft, the -m option was named -b (for Base64), but it was
282 renamed to reflect its relationship to the RFC 2045. A -u was also
283 present to invoke the default algorithm, but since this was not histor‐
284 ical practice, it was omitted as being unnecessary.
285 See the RATIONALE section in uudecode for the derivation of the
287 /dev/stdout symbol.
288
290 None.
291
293 chmod, mailx, uudecode
294 The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment
296 Variables, Section 12.2, Utility Syntax Guidelines
297
299 Portions of this text are reprinted and reproduced in electronic form
300 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
301 table Operating System Interface (POSIX), The Open Group Base Specifi‐
302 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
303 Electrical and Electronics Engineers, Inc and The Open Group. In the
304 event of any discrepancy between this version and the original IEEE and
305 The Open Group Standard, the original IEEE and The Open Group Standard
306 is the referee document. The original Standard can be obtained online
307 at http://www.opengroup.org/unix/online.html .
308 Any typographical or formatting errors that appear in this page are
310 most likely to have been introduced during the conversion of the source
311 files to man page format. To report such errors, see https://www.ker‐
312 nel.org/doc/man-pages/reporting_bugs.html .
313IEEE/The Open Group 2017 UUENCODE(1P)