How do I decode a MIME/BASE64 string?

The MIME-Base64 package (available from CPAN) handles this as well as the MIME/QP encoding. Decoding BASE64 becomes as simple as:

    use MIME::Base64;
    $decoded = decode_base64($encoded);

The MIME-Tools package (available from CPAN) supports extraction with decoding of BASE64 encoded attachments and content directly from email messages.

If the string to decode is short (less than 84 bytes long) a more direct approach is to use the unpack() function's "u" format after minor transliterations:

    tr#A-Za-z0-9+/##cd;                   # remove non-base64 chars
    tr#A-Za-z0-9+/# -_#;                  # convert to uuencoded format
    $len = pack("c", 32 + 0.75*length);   # compute length byte
    print unpack("u", $len . $_);         # uudecode and print

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