base64.1

base64编码

.TH BASE64 1 "20 FEB 2001"
.UC 4
.SH NAME
base64 \- encode / decode binary file as RFC 1341 MIME base64
.SH SYNOPSIS
.B base64
.BR \-d | \-e 
[
.B \-n
]
[
.B \-u
]
[
.I infile
[
.I outfile
] ]
.SH DESCRIPTION
The MIME (Multipurpose Internet Mail Extensions) specification
(RFC 1341 and successors) defines a mechanism for encoding arbitrary binary
information for transmission by electronic mail.  Triplets
of 8-bit octets are encoded as groups of four characters,
each representing 6 bits of the source 24 bits.  Only characters
present in all variants of ASCII and EBCDIC are used, avoiding
incompatibilities in other forms of encoding such as
.BR uuencode / uudecode .
.PP
.B base64
is a command line utility which encodes and decodes files in this format.
It can be used within a pipeline as an encoding or decoding filter,
and is most commonly used in this manner as part of an automated
mail processing system.
.SH OPTIONS
.TP 12
.B \-\-copyright
Print program copyright information.
.TP
.BR \-d ", " \-\-decode
Decodes the input, previously created by
.BR base64 ,
to recover the original input file.
.TP
.BR \-e ", " \-\-encode
Encodes the input into an output text file containing
its base64 encoding.
.TP
.BR \-n ", " \-\-noerrcheck
Suppress error checking when decoding.  By default, upon encountering
a non white space character which does not belong to the base64
set, or discovering the input file is incorrectly padded to a
multiple of four characters,
.B base64
issues an error message and terminates
processing with exit status 1.  The
.B \-n
option suppresses even this rudimentary error checking; invalid
characters are silently ignored and the output truncated to the
last three valid octets if the input is incorrectly padded.
.TP
.BR \-u ", " \-\-help
Print how-to-call information.
.TP
.B \-\-version
Print program version information.
.SH EXIT STATUS
.B base64
returns status 0 if processing was completed without errors, 1 if an
I/O error occurred or errors were detected in decoding a file which
indicate it is incorrect or incomplete, and 2 if processing
could not be performed at all due, for example, to a nonexistent input
file.
.SH FILES
If no
.I infile
is specified or
.I infile
is a single ``\-'',
.B base64
reads from standard input; if no
.I outfile
is given, or
.I outfile
is a single ``\-'',
output is sent to standard output.  The input and
output are processed strictly serially; consequently
.B base64
may be used in pipelines.
.SH BUGS
Little or no error checking is done when decoding, other than
validating that the input consists of a multiple of four
characters in the encoding set.  This is inherent in the
design of base64, which assumes transmission integrity is
the responsibility of a higher-level protocol.
.PP
Please report bugs and documentation errors to
.BR [e-mail] .
.SH "SEE ALSO"
.PD
.BR uudecode (1),
.BR uuencode (1),
RFC1341
.ne 4
.SH AUTHOR
.RS 5
.nf
John Walker
http://www.fourmilab.ch/
.fi
.RE
.PD
.PP
This software is in the public domain.
Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted,
without any conditions or restrictions.  This software is provided ``as
is'' without express or implied warranty.
.PP
This is version 1.3 of
.BR base64 .
The current version of this program may be downloaded from
http://www.fourmilab.ch/webtools/base64.