The uudecode utility shall read a file, or standard input if no file is
specified, that includes data created by the uuencode utility. The
uudecode utility shall scan the input file, searching for data
compatible with one of the formats specified in uuencode, and attempt
to create or overwrite the file described by the data (or overridden by the
-o option). The pathname shall be contained in the data or specified by
the -o option. The file access permission bits and contents for the
file to be produced shall be contained in that data. The mode bits of the
created file (other than standard output) shall be set from the file access
permission bits contained in the data; that is, other attributes of the mode,
including the file mode creation mask (see umask() ), shall not affect
the file being produced.
If the pathname of the file to be produced exists, and the user does not have
write permission on that file, uudecode shall terminate with an error.
If the pathname of the file to be produced exists, and the user has write
permission on that file, the existing file shall be overwritten.
If the input data was produced by uuencode on a system with a different
number of bits per byte than on the target system, the results of
uudecode are unspecified.
The following environment variables shall affect the execution of
Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
If set to a non-empty string value, override the values of
all the other internationalization variables.
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.
Determine the location of message catalogs for the
processing of LC_MESSAGES.
If the file data header encoded by uuencode is - or
/dev/stdout, or the -o/dev/stdout option overrides the
file data, the standard output shall be in the same format as the file
originally encoded by uuencode. Otherwise, the standard output shall
not be used.
The user who is invoking uudecode must have write permission on any file
The output of uuencode is essentially an encoded bit stream that is not
cognizant of byte boundaries. It is possible that a 9-bit byte target machine
can process input from an 8-bit source, if it is aware of the requirement, but
the reverse is unlikely to be satisfying. Of course, the only data that is
meaningful for such a transfer between architectures is generally character
Input files are not necessarily text files, as stated by an early proposal.
Although the uuencode output is a text file, that output could have
been wrapped within another file or mail message that is not a text file.
The -o option is not historical practice, but was added at the request of
WG15 so that the user could override the target pathname without having to
edit the input data itself.
In early drafts, the [ -ooutfile] option-argument allowed the use
of - to mean standard output. The symbol - has only been used
previously in IEEE Std 1003.1-2001 as a standard input
indicator. The developers of the standard did not wish to overload the meaning
of - in this manner. The /dev/stdout concept exists on most
modern systems. The /dev/stdout syntax does not refer to a new special
file. It is just a magic cookie to specify standard output.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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