Intro To 'base64' Command In Linux

2023-09-20 - By Robert Elder

I use the 'base64' command to encode or decode from base64 encoding:

echo "base64" | base64

YmFzZTY0Cg==

If I pipe this hello world statement into the 'base64' command, I'll see the following string of base 64 characters:

echo "Hello World!" | base64

SGVsbG8gV29ybGQhCg==

I can also decode this same base 64 encoded string by using the '-d' flag:

echo "SGVsbG8gV29ybGQhCg==" | base64 -d

Hello World!

RFC 4648

The 'base64' character set is defined in request for comment 4648. In this table, you can see that the 'base64' encoding uses all uppercase and lowercase letters of the alphabet, as well as the digits 0 to 9 and the plus and forward slash characters:

                      Table 1: The Base 64 Alphabet

     Value Encoding  Value Encoding  Value Encoding  Value Encoding
         0 A            17 R            34 i            51 z
         1 B            18 S            35 j            52 0
         2 C            19 T            36 k            53 1
         3 D            20 U            37 l            54 2
         4 E            21 V            38 m            55 3
         5 F            22 W            39 n            56 4
         6 G            23 X            40 o            57 5
         7 H            24 Y            41 p            58 6
         8 I            25 Z            42 q            59 7
         9 J            26 a            43 r            60 8
        10 K            27 b            44 s            61 9
        11 L            28 c            45 t            62 +
        12 M            29 d            46 u            63 /
        13 N            30 e            47 v
        14 O            31 f            48 w         (pad) =
        15 P            32 g            49 x
        16 Q            33 h            50 y

Additionally, an equal sign character is used for padding.

Purpose Of Base 64 Encoding

The 'base64' command is useful for reliably encoding non-printable binary characters into a form that can't be easily corrupted by other programs:

echo -n -e '\x00\x01\x02\x95\x96\x97' | xxd

00000000: 0001 0295 9697                           ......

echo -n -e '\x00\x01\x02\x95\x96\x97' | base64

AAEClZaX

echo -n -e '\x00\x01\x02\x95\x96\x97' | base64 | base64 -d | xxd

00000000: 0001 0295 9697                           ......

Base 32 Vs. Base 64

Base 64 is more efficient at representing information than base 32:

echo 'Hello World!' | base32

JBSWY3DPEBLW64TMMQQQU===

echo 'Hello World!' | base64

SGVsbG8gV29ybGQhCg==

echo 'Hello World!' | base32 | wc -c

echo 'Hello World!' | base64 | wc -c

Disadvantage Of Base 64

One disadvantage of base 64 is that it's larger character set means there are more ways for base64 encoded data to become corrupted in transit, as illustrated by the following example:

#  Convert to all lowercase, then to all uppercase:
echo 'Hello World!' | base32 | tr 'A-Z' 'a-z' | tr 'a-z' 'A-Z' | base32 -d

Hello World!

#  Convert to all lowercase, then to all uppercase:
echo 'Hello World!' | base64 | tr 'A-Z' 'a-z' | tr 'a-z' 'A-Z' | base64 -d

HeRoWoX

And that's why the 'base64' command is my favourite Linux command.

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