MIME::Base64(3perl) Perl Programmers Reference Guide MIME::Base64(3perl)
NAME
MIME::Base64 - Encoding and decoding of base64 strings
SYNOPSIS
use MIME::Base64;
$encoded = encode_base64('Aladdin:open sesame');
$decoded = decode_base64($encoded);
DESCRIPTION
This module provides functions to encode and decode strings into and
from the base64 encoding specified in RFC 2045 - MIME (Multipurpose
Internet Mail Extensions). The base64 encoding is designed to represent
arbitrary sequences of octets in a form that need not be humanly
readable. A 65-character subset ([A-Za-z0-9+/=]) of US-ASCII is used,
enabling 6 bits to be represented per printable character.
The following primary functions are provided:
encode_base64( $bytes )
encode_base64( $bytes, $eol );
Encode data by calling the encode_base64() function. The first
argument is the byte string to encode. The second argument is the
line-ending sequence to use. It is optional and defaults to "\n".
The returned encoded string is broken into lines of no more than 76
characters each and it will end with $eol unless it is empty. Pass
an empty string as second argument if you do not want the encoded
string to be broken into lines.
The function will croak with "Wide character in subroutine entry" if
$bytes contains characters with code above 255. The base64 encoding
is only defined for single-byte characters. Use the Encode module
to select the byte encoding you want.
decode_base64( $str )
Decode a base64 string by calling the decode_base64() function.
This function takes a single argument which is the string to decode
and returns the decoded data.
Any character not part of the 65-character base64 subset is silently
ignored. Characters occurring after a '=' padding character are
never decoded.
If you prefer not to import these routines into your namespace, you can
call them as:
use MIME::Base64 ();
$encoded = MIME::Base64::encode($decoded);
$decoded = MIME::Base64::decode($encoded);
Additional functions not exported by default:
encode_base64url( $bytes )
decode_base64url( $str )
Encode and decode according to the base64 scheme for "URL
applications" [1]. This is a variant of the base64 encoding which
does not use padding, does not break the string into multiple lines
and use the characters "-" and "_" instead of "+" and "/" to avoid
using reserved URL characters.
encoded_base64_length( $bytes )
encoded_base64_length( $bytes, $eol )
Returns the length that the encoded string would have without
actually encoding it. This will return the same value as
"length(encode_base64($bytes))", but should be more efficient.
decoded_base64_length( $str )
Returns the length that the decoded string would have without
actually decoding it. This will return the same value as
"length(decode_base64($str))", but should be more efficient.
EXAMPLES
If you want to encode a large file, you should encode it in chunks that
are a multiple of 57 bytes. This ensures that the base64 lines line up
and that you do not end up with padding in the middle. 57 bytes of data
fills one complete base64 line (76 == 57*4/3):
use MIME::Base64 qw(encode_base64);
open(FILE, "/var/log/wtmp") or die "$!";
while (read(FILE, $buf, 60*57)) {
print encode_base64($buf);
}
or if you know you have enough memory
use MIME::Base64 qw(encode_base64);
local($/) = undef; # slurp
print encode_base64(<STDIN>);
The same approach as a command line:
perl -MMIME::Base64 -0777 -ne 'print encode_base64($_)' <file
Decoding does not need slurp mode if every line contains a multiple of
four base64 chars:
perl -MMIME::Base64 -ne 'print decode_base64($_)' <file
Perl v5.8 and better allow extended Unicode characters in strings. Such
strings cannot be encoded directly, as the base64 encoding is only
defined for single-byte characters. The solution is to use the Encode
module to select the byte encoding you want. For example:
use MIME::Base64 qw(encode_base64);
use Encode qw(encode);
$encoded = encode_base64(encode("UTF-8", "\x{FFFF}\n"));
print $encoded;
COPYRIGHT
Copyright 1995-1999, 2001-2004, 2010 Gisle Aas.
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
Distantly based on LWP::Base64 written by Martijn Koster
<m.koster@nexor.co.uk> and Joerg Reichelt <j.reichelt@nexor.co.uk> and
code posted to comp.lang.perl <3pd2lp$6gf@wsinti07.win.tue.nl> by Hans
Mulder <hansm@wsinti07.win.tue.nl>
The XS implementation uses code from metamail. Copyright 1991 Bell
Communications Research, Inc. (Bellcore)
SEE ALSO
MIME::QuotedPrint
[1] <http://en.wikipedia.org/wiki/Base64#URL_applications>
perl v5.40.1 2026-08-30 MIME::Base64(3perl)
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