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Encoding and decoding of base64 strings

MIME::Base64 - Encoding and decoding of base64 strings


MIME::Base64 - Encoding and decoding of base64 strings


 use MIME::Base64;

 $encoded = encode_base64('Aladdin:open sesame');

 $decoded = decode_base64($encoded);


This module provides functions to encode and decode strings into 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 functions are provided:

encode_base64($str, [$eol])
Encode data by calling the encode_base64() function. The first argument is the 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 broken into lines.

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 set is silently ignored. Characters occuring after a '=' padding character are never decoded.

If the length of the string to decode (after ignoring non-base64 chars) is not a multiple of 4 or padding occurs too early, then a warning is generated if perl is running under -w.

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);


The following warnings might be generated if perl is invoked with the -w switch:

Premature end of base64 data
The number of characters to decode is not a multiple of 4. Legal base64 data should be padded with one or two ``='' characters to make its length a multiple of 4. The decoded result will anyway be as if the padding was there.

Premature padding of base64 data
The '=' padding character occurs as the first or second character in a base64 quartet.


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 all the lines contains a multiple of 4 base64 chars:

   perl -MMIME::Base64 -ne 'print decode_base64($_)' <file


Copyright 1995-1999, 2001 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 <> and Joerg Reichelt <> and code posted to comp.lang.perl <3pd2lp$> by Hans Mulder <>

The XS implementation use code from metamail. Copyright 1991 Bell Communications Research, Inc. (Bellcore)